The Secret Mechanics of High Feed End Mills

A High Feed End Mill is a type of High-Efficiency Milling (HEM) tool with a specialized end profile that allows the tool to utilize chip thinning to have dramatically increased feed rates. These tools are meant to operate with an extremely low axial depth so that the cutting action takes place along the curved edge of the bottom profile. This allows for a few different phenomena to occur:

  • The low lead angle causes most of the cutting force to be transferred axially back into the spindle. This amounts to less deflection, as there is much less radial force pushing the cutter off its center axis.
  • The extended curved profile of the bottom edge causes a chip thinning effect that allows for aggressive feed rates.

Low Lead Angle

As seen in Figure 1 below, when a High Feed End Mill is properly engaged in a workpiece, the low lead angle, combined with a low axial depth of cut, transfers the majority of the cutting force upward along the center axis of the tool. A low amount of radial force allows for longer reaches to be employed without the adverse effects of chatter, which will lead to tool failure. This is beneficial for applications that require a low amount of radial force, such as machining thin walls or contouring deep pockets.

high feed mill roughing
Figure 1: Isometric view of a feed mill engaged in a straight roughing pass (left), A snapshot front-facing view of this cut (right)

Aggressive Feed Rates

Figure 1 also depicts an instantaneous snapshot of the chip being formed when engaged in a proper roughing tool path. Notice how the chip (marked by diagonal lines) thins as it approaches the center axis of the tool. This is due to the curved geometry of the bottom edge. Because of this chip thinning phenomenon, the feed of the tool must be increased so that the tool is actively engaged in cutting and does not rub against the workpiece. Rubbing will increase friction, which in turn raises the level of heat around the cutting zone and causes premature tool wear. Because this tool requires an increased chip load to maintain a viable cutting edge, the tool has been given the name “High Feed Mill.”

Other Phenomena Due to Curved Geometry of Bottom Edge

The curved geometry of the bottom edge also sanctions for the following actions to occur:

  • A programmable radius being added to a CAM tool path
  • Scallops forming during facing operations
  • Different-shaped chips created during slotting applications, compared to HEM roughing

Programmable Radius

Helical Solutions’ High Feed End Mills has a double radius bottom edge design. Because of this, the exact profile cannot be easily programmed by some CAM software. Therefore, a theoretical radius is used to allow for easy integration.  Simply program a bullnose tool path and use the theoretical radius (seen below in Figure 2) from the dimensions table as the corner radius.

high feed mill programmable radius
Figure 2: Programmable radius of a double radius profile tool

Managing Scallops:

A scallop is a cusp of material left behind by cutting tools with curved profiles. Three major factors that determine the height and width of scallops are:

  1. Axial Depth of Cut
  2. Radial Depth of Cut
  3. Curvature of Bottom Edge or Lead Angle

Figure 3 below is a depiction of the scallop profile of a typical roughing cut with a 65% radial step over and 4% axial depth of cut. The shaded region represents the scallop that is left behind after 2 roughing passes and runs parallel to the tool path.

roughing cut scallop profile
Figure 3: Back view of roughing cut with a 65% radial step over

Figures 4 and 5 show the effects of radial and axial depth of cuts on the height and width of scallops. These figures should be viewed in the context of Figure 3. Percentage by diameter is used rather than standard units of measurement to show that this effect can be predicted at any tool size. Figure 4 shows that a scallop begins to form when the tool is programmed to have a radial step over between 35% and 40%. The height increases exponentially until it is maximized at the axial depth of cut. Figure 5 shows that there is a linear relationship between the radial step over and scallop width. No relationship is seen between scallop width and axial depth of cut as long as ADOC and the radius of curvature of the bottom cutting edge remains consistent.

graph of scallop height versus depth of cut
Figure 4: Graph of Scallop Height vs. Depth of Cut
graph of scallop width versus depth of cut
Figure 5: Scallop Width vs. Depth of Cut

From the graphs in Figures 4 and 5 we get the following equations for scallop dimensions.

Notes regarding these equations:

  • These equations are only applicable for Helical Solutions High Feed End Mills
  • These equations are approximations
  • Scallop height equation is inaccurate after the axial depth of cut is reached
  • RDOC is in terms of diameter percentage (.55 x Diameter, .65 x Diameter, etc…)

Curvature of Bottom Edge

The smaller the radius of curvature, the larger the height of the scallop. For example, the large partial radius of the Helical Solutions High Feed End Mill bottom cutting edge will leave a smaller scallop when compared to a ball end mill programmed with the same tool path. Figure 6 shows a side by side comparison of a ball end mill and high feed mill with the same radial and axial depth of cut. The scallop width and height are noticeably greater for the ball end mill because it has a smaller radius of curvature.

feed mill versus ball end mill
Figure 6: Scallop diagram of High Feed Mill and Ball End Mill with the same workpiece engagement

Full Slotting

When slotting, the feed rate should be greatly reduced relative to roughing as a greater portion of the bottom cutting edge is engaged. As shown in Figure 7, the axial step down does not equate to the axial engagement. Once engaged in a full slot, the chip becomes a complex shape. When viewing the chip from the side, you can see that the tool is not cutting the entirety of the axial engagement at one point in time. The chip follows the contour on the slot cut in the form of the bottom edge of the tool. Because of this phenomenon, the chip dips down to the lowest point of the slot and then back up to the highest point of axial engagement along the side. This creates a long thin chip that can clog up the small flute valleys of the tool, leading to premature tool failure. This can be solved by decreasing the feed rate and increasing the amount of coolant used in the operation.

high feed mill chip formation
Figure 7: Formation of a chip when a feed mill is engaged in a full slotting operation.

In summary, the curved profile of the bottom edge of the tool allows for higher feed rates when high feed milling, because of the chipping thinning effect it creates with its low lead angle. This low lead angle also distributes cutting forces axially rather than radially, reducing the amount of chatter that a normal end mill might experience under the same conditions. Machinists must be careful though as the curved bottom edge also allows for the formation of scallops, requires a programmable radius when using some CAM packages, and make slotting not nearly as productive as roughing operations.

Causes & Effects of Built-Up Edge (BUE) in Turning Applications

In turning operations, the tool is stationary while the workpiece is rotating in a clamped chuck or a collet holder. Many operations are performed in a lathe, such as facing, drilling, grooving, threading, and cut-off applications. it is imperative to use the proper tool geometry and cutting parameters for the material type that is being machined. If these parameters are not applied correctly in your turning operations, built-up edge (BUE), or many other failure modes, may occur. These failure modes adversely affect the performance of the cutting tool and may lead to an overall scrapped part.

When inspecting a cutting tool under a microscope or eye loupe, there are several different types of turning tool failure modes that can be apparent. Some of the most common modes are:

  • Normal Flank Wear: The only acceptable form of tool wear, caused by the normal aging of a used cutting tool and found on the cutting edges.
    • This abrasive wear, caused by hard constituents in the workpiece material, is the only preferred method of tool wear, as it’s predictable and will continue to provide stable tool life, allowing for further optimization and increased productivity.
  • Cratering: Deformations found on the cutting face of a tool.
    • This tool mode is a chemical and heat failure, localized on the rake face area of the turning tool, or insert. This failure results from the chemical reaction between the workpiece material and the cutting tool and is amplified by cutting speed. Excessive Crater Wear weakens a turning tool’s cutting edge and may lead to cutting edge failure.
  • Chipping: Breaking of the turning tool along its cutting face, resulting in an inaccurate, rough cutting edge.
    • This is a mechanical failure, common in interrupted cutting or non-rigid machining setups. Many culprits can be to blame for chipping, including machine mishaps and tool holder security.
  • Thermal Mechanical Failure (Thermal Cracking): The cracking of a cutting tool due to significant swings in machining temperature.
    • When turning, heat management is key. Too little or too much heat can create issues, as can significant, fast swings in temperature (repeated heating and cooling on the cutting edge). Thermal Mechanical Failure usually shows in the form of evenly spaced cracks, perpendicular to the cutting edge of the turning tool.
  • Built-Up Edge (BUE): When chips adhere to the cutting tool due to high heat, pressure, and friction.

Effects of Built-Up Edge in Turning Application

A built-up edge is perhaps the easiest mode of tool wear to identify, as it may be visible without the need for a microscope or an eye loupe. The term built-up edge means that the material that you’re machining is being pressure welded to the cutting tool. When inspecting your tool, evidence of a BUE problem is material on the rake face or flank face of the cutting tool.

built up cutting edge on turning tools
Image Source: Carbide inserts Wear Failure modes. | machining4.eu, 2020

This condition can create a lot of problems with your machining operations, such as poor tool life, subpar surface finish, size variations, and many other quality issues. The reason for these issues is that the centerline distance and the tool geometry of the cutting edge are being altered by the material that’s been welded to the rake or flank face of the tool. As the BUE condition worsens, you may experience other types of failures or even catastrophic failure.                     

Causes of Built-Up Edge in Turning Applications

Improper Tooling Choice

Built-Up Edge is oftentimes caused by using a turning tool that does not have the correct geometry for the material being machined. Most notably, when machining a gummy material such as aluminum or titanium, your best bet is to use tooling with extremely sharp cutting edges, free cutting geometry, and a polished flank and rake face. This will not only help you to cut the material swiftly but also to keep it from sticking to the cutting tool.

various turning tools

Using Aged Tooling

Even when using a turning tool with correct geometry, you may still experience BUE. As the tool starts to wear and its edge starts to degrade, the material will start building up on the surface of the tool. For this reason, it is very important to inspect the cutting edge of a tool after you have machined a few parts, and then randomly throughout the set tool life. This will help you identify the root cause of any of the failure modes by identifying them early on.

Insufficient Heat Generation

Built-up edge can be caused from running a tool at incorrect cutting parameters. Usually, when BUE is an issue, it’s due to the speed or feed rates being too low. Heat generation is key during any machining application – while too much heat can impact a part material, too little can cause the tool to be less effective at efficiently removing chips.

4 Simple Ways to Mitigate BUE in Turning Applications

  1. When selecting a tool, opt for free cutting, up sharp geometries with highly polished surfaces. Selecting a tool with chipbreaker geometry will also help to divide chips, which will help to remove it from the part and the cutting surface.
  2. Be confident in your application approach and your running parameters. It’s always important to double-check that your running parameters are appropriate for your turning application.
  3. Make sure the coolant is focused on the cutting edge and increase the coolant concentration amount.
  4. Opt for a coated Insert, as coatings are specifically engineered for a given set of part materials, and are designed to prevent common machining woes.
solid carbide turning tool

Achieving Success in CNC Woodworking

Developing a Successful Cutting Direction Strategy

There are a number of factors that can affect the machining practices of wood in woodworking. One that comes up a lot for certain hardwoods is the cutting direction, specifically in relation to the grain pattern of the wood. Wood is an anisotropic material. This means that different material properties are exhibited in different cutting directions. In terms of lumber, there are different structural grades of wood related to grain orientation. If the average direction of the cellulose fibers are parallel to the sides of the piece of lumber, then the grains are said to be straight. Any deviation from this parallel line and the board is considered to be “cross-grain”. Figure 1 below depicts a mostly straight grain board with arrows indicating the different axes. Each of these axes exhibits different sets of mechanical properties. Because of these differences, one must be conscious of the tool path in woodworking and minimize the amount of cutting forces placed on the cutter in order to maximize its tool life.

straight grain wood board with woodworking axes
Figure 1: Mostly straight grain board with arrows indicating different axes

Cutting perpendicular to the grain is known as cutting “across the grain” in woodworking. In Figure 1 above, this would be considered cutting in the radial or tangential direction. Cutting parallel to the grain is known as cutting “along the grain” (longitudinally in terms of Figure 1). The closer you are to cutting at 90° to the grain of the wood in any direction, the larger the cutting force will be. For example, a tool with its center axis parallel to the tangential direction and a tool path along the longitudinal direction would have less wear than a tool with the same center axis but moving in the radial direction. The second type of tool orientation is cutting across more grain boundaries and therefore yields greater cutting forces. However, you must be careful when cutting along the grain as this can cause tear-outs and lead to a poor surface finish.

The Proper Formation of Wood Chips With CNC Woodworking

When cutting wood parallel to the grain, there are three basic types of chips that are formed. When cutting perpendicular to the grain, the chip types generally fall into these same 3 categories, but with much more variability due to the wide range in wood properties with respect to the grain direction.

Type 1 Chips

Type 1 chips are formed when wood splits ahead of the cutting edge through cleavage until failure in bending occurs as a cantilever beam. A large force perpendicular to the shear plane is produced, causing the wood ahead of the cutting edge to split, forming this tiny cantilever beam. When the upward force finally exceeds the strength of this tiny beam, it breaks off.  These types of chips cause comparatively little wear compared to types 2 and 3, as the material is splitting before coming in contact with the pointed edge. End mills with either extremely high rake or very low rake angles often produce type 1 chips. This is especially true when machining against grain slopes that are greater than 25°. Woods with moisture content less than 8%form discontinuous chips and are at a higher risk of tear-out.

Type 2 Chips

Type 2 chips are the most desirable of the three types in terms of surface finish. They are a result of material failure along a diagonal shear plane, extending from the cutting edge to the workpiece surface. Type 2 chips form when there is a proper balance between the properties of the wood, cutting parameters, and cutter geometry. Woods with a moisture content between 8% and 20%have a much higher chance of forming continuous type 2 chips while leaving a good surface finish.

Type 3 Chips

The last type of chip forms when the rake angle of a cutter is much too low. In this scenario, the cutting force is almost parallel to the direction of travel. This causes a soft material, such as wood, to be crushed rather than sheared away, leaving a poor surface finish. Generally, the surface left behind looks like tiny bundles of wood elements, a surface defect commonly known as “fuzzy grain.” This type of chip occurs more frequently in softwoods as the crushing situation is compounded in low-density woods.

types of wood chips in woodworking
Figure 2: Different types of wooden chips

Extending Tool Life When Woodworking

Speeds & Feeds Rules of Thumb

There are several different categories of tool wear that occur when cnc woodworking. General rules of machining still apply as RPM has the greatest influence on wear rate. Over-feeding can increase tool wear exponentially and also cause tool breakage. As with most machining operations, a balance between these two is essential. If you are looking to increase your productivity by increasing your speed, you must increase your feed proportionally in order to maintain a balance that keeps the tool properly engaged in the material.

Proper Management of Heat

When cutting tools are exposed to high heat, they begin to wear even faster, due to corrosion. The cobalt binder within most carbide tools on the market begins to oxidize and break free of the cutting edge. This sets off a chain reaction, as when the binder is removed, the tungsten carbide breaks away, too. Different species of wood and types of engineered wood have different corrosive behaviors at high temperatures. This is the most consistent type of wear that is observed when machining MDF or particleboard. The wear is due to the chlorine and sulfate salts found in adhesives as this accelerates high-temperature corrosion.  As with aluminum, when the silica content of a wood increases, so too does its corrosiveness.

Generally, increased tool wear is observed in wood with high moisture content. This trait is due to the increased electro-chemical wear caused by the extractives in wood., Moisture content in wood includes substances such as resins, sugars, oils, starches, alkaloids, and tannins in the presence of water. These molecules react with the metallic constitutes of the cutting tool and can dull the cutting edge. Carbide is more resistant to this type of wear compared to high-speed steel.

Best Coatings for Extended Tool Life in Wood

If you want a longer-lasting tool that will maintain its sharp cutting edge (and who doesn’t), you may want to consider an Amorphous Diamond coating. This is an extremely abrasive resistant coating meant for non-ferrous operations in which the temperature of the cutting zone does not exceed 750 °F. This coating type is one of Harvey Tool’s thinnest coatings, therefore minimizing the risk of any edge rounding and maximizing this edge’s durability.

Avoiding Common Woodworking Mishaps

Tear Out

Tear out, sometimes called chipped grain or splintering, is when a chunk of the wood material being machined tears away from the main workpiece and leaves an unappealing defect where it used to be. This is one of the most common defects when machining wood products. There are many different reasons that tear out occurs. Material characteristics are something to be considered. Tear out is more likely to occur if the grain orientation is less than 20°relative to the tool path, the moisture content of the wood is too low, or the density of the wood is too low. Figure 4 shows the grain orientation angle relative to the tool path. In terms of machining parameters, it can also occur if either the chip load, depth of cut, or rake angle is too high.

woodworking grain in relation to tool path
Figure 4: Example of grain orientation angle relative to the tool path

Fuzzy Grain Finish

Fuzzy grain looks like small clumps of wood attached to the newly machined face and occurs when the wood fibers are not severed properly. Low rake or dull cutting tools indent fibers until they tear out from their natural pattern inside, causing type 3 chips to form, resulting in a poor finish. This can be exacerbated by a low feed or depth of cut as the tool is not properly engaged and is plowing material rather than shearing it properly. Softer woods with smaller and lesser amounts of grains are more susceptible to this type of defect. Juvenile wood is known to be particularly liable for fuzzy grain because of its high moisture content.

fuzzy grain wood finish
Figure 5: Example of a fuzzy grain finish

Burn Marks

Burn Marks are a defect that is particularly significant in the case of machining wood, as it is not generally a concern when machining other materials. Dwelling in a spot for too long, not engaging enough of the end mill in a cut, or using dull tools creates an excessive amount of heat through friction, which leaves burn marks. Some woods (such as maple or cherry) are more susceptible to burn marks, therefore tool paths for these types should be programmed sensibly. If you are having a lot of trouble with burn marks in a particular operation, you may want to try spraying the end mill with a commercial lubricant or paste wax. Be careful not to use too much as the excess moisture can cause warping. Increasing your tool engagement or decreasing RPM may also combat burn marks.

burn marks from wood cutter
Figure 6: Example of burn marks

Chip Marks

Chip marks are shallow compressions in the surface of the wood that have been sprayed or pressed into the surface. These defects can swell with an increase in moisture content, worsening the finish even more. This type of blemish is generally caused by poor chip evacuation and can usually be fixed by applying air blast coolant to the cutting region during the operation.

Raised Grain

Raised grain, another common defect of woods, is when one or more portions of the workpiece are slightly lower than the rest. This blemish is particularly a problem when machining softer woods with dull tools as the fibers will tear and deform rather than be cleanly sheared away. This effect is intensified when machining with slow feeds and the wood has a high moisture content. Variations in swelling and shrinking between damaged and undamaged sections of wood exacerbate this flaw. It’s for this reason that raised grain is a common sight on weather-beaten woods. Work holding devices that are set too tight also have a chance of causing raised grain.

Differentiating Harvey Tool Wood Cutting & Plastic Cutting End Mills

Machinists oftentimes use Plastic Cutting End Mills for woodworking, as this tool has very similar internal geometries to that of an End Mill for Wood. Both tools have large flute valleys and sharp cutting edges, advantageous for the machining of both plastic and wood. The main difference between the Harvey Tool plastic cutters and the woodcutters is the wedge angle (a combination of the primary relief and rake angle). The woodcutter line has a lower rake but still has a high relief angle to maintain the sharpness of the cutting edge. The lower rake is designed to not be as “grabby” as the plastic cutters can be when woodworking. It was meant to shear wood and leave a quality surface finish by not causing tear-out.

Harvey Tool’s offering of End Mills for Wood includes both upcut and downcut options. The upcut option is designed for milling natural and engineered woods, featuring a 2-flute style and a wedge angle engineered for shearing wood fiber materials without causing tear out or leaving a fuzzy grain finish. The downcut offering is optimized for milling natural and engineered woods and helps prevent lifting on vacuum tables.

For more help on achieving a successful machining operation, or more information on Harvey Tool’s offering of End Mills for Wood, please contact Harvey Tool’s team of engineers at 800-645-5609.

Schon DSGN – Featured Customer

In 2012, engineer Ian Schon wanted to put his skill for design to the test. He decided to challenge himself by designing a normal, everyday item: a pen. His goal was to take the pen from the design concept to manufacturing it within his own shop. Ian designed his pen how he thought a pen should be: durable, reliable, compact, leak-proof, and easy to use. Most of all, though, he wanted the pen to be of a superior quality, not something easily lost or thrown away.

With the design concept in place, Ian started his work on engineering and manufacturing his new pen. He made many prototypes, and with each discovered new features and additions to better his design. Today, Ian manufacturers his pens through local fabrications in Massachusetts, using local supplies. He makes them from 6061 Aluminum, unique in that it molds to its users’ hand, over time. His pens are designed to outlast its user and be passed on through generations.

Ian was kind enough to take time out of his busy schedule to answer some questions about his manufacturing success.

Schon DSGN silver wrist watch with black band

What sets Schon DSGN apart from competition?

I think I have a unique approach to designing and manufacturing. I design things that I like, and make them the way that I want to.  I don’t rush things out the door. I’m not thinking about scale, growth, making a big shop, etc. I just want to live a simple life where I make cool objects, sell them, and have enough time in the week to sneak out into the woods and ride my bike. This ethos takes the pressure off a lot, and that makes the workflow freer without as much stress as I had in my past career as a product development engineer.

This workflow isn’t for everyone. it’s not a winning combo for massive business success, per se, and if you audited me you would tell me I’m holding back by not scaling and hiring, but I like it. I see myself as a hybrid between artist and entrepreneur. I love doing things start to finish, blank paper to finished part on the machine. Owning that entire workflow allows for harmony of engineering, machining, tooling, finishing, R+D, marketing, etc. Further, it ensures that I don’t miss critical inflection points in the process that are ripe for process evolution and innovation, resulting in a better product in the end.

I’m sure the way I do things will change over time, but for now I’m still figuring things out and since I work largely alone (I have one amazing helper right now assisting with assembly, finishing, and shipping) I have lots of flexibility to change things and not get stuck in my ways.

Also, by working alone, I control the music. Key!

schon dsgn turning metal on lathe

Where did your passion for pens come from?

My friend Mike had a cool pen he got from a local shop and I was like “man I like that,” so I made one with some “improvements.” At the time, in my mind, they were improvements, but I have learned now that they were preferences, really. I made a crappy pen on a lathe at the MIT MITERS shop back in 2010, and that summer I bought a Clausing lathe on craigslist for $300 and some tooling and started figuring it all out. I made a bunch of pens, wrote with them, kept evolving them, and eventually people asked me to make pens for them.  I didn’t really intend to start a business or anything, I just wanted to make cool stuff and use it. Bottle openers, knives, bike frames, etc. I made lots of stuff. Pens just stuck with me and I kept pushing on it as a project for my design portfolio. Eventually it became something bigger. Turns out my pen preferences were shared with other people.

Schon dsgn gold and copper metal pens

What is the most difficult product you have had to make and why?

Making watch cases – wow. What an awful part to try and make on a desktop Taig 3 axis mill and a Hardinge lathe in my apartment! I started working on machining watch cases in 2012, and I finished my first one in my apartment in 2015 (to be fair, I was working on lots of other stuff during that time! But yeah, years…). What a journey. Taught me a lot. Biting off more than you can chew is a great way to learn something. 

What is the most interesting product you’ve made?

When I worked at Essential Design in Boston I worked on the front end of a Mass Spectrometer. The requirements on the device were wild. We had high voltage, chemical resistance, crazy tolerances, mechanism design, machining, injection molding – truly a little bit of everything! It was a fun challenge that I was fortunate to be a part of. Biomolecule nanoscale analysis device. Try saying that ten times fast.

I have something fountain pen related in the works now that I find more interesting, and very, very complex, but it’s under wraps a bit longer. Stay tuned. 

Schon dsgn gold and copper metal pens

Who is the most famous contact that you have worked on a project with?

I have made watches for some incredible customers, but I unfortunately cannot talk about who they are. Most of my watch work outside of my own parts is also under NDA which is a bummer, but hey it was great work regardless.

Same thing with the pens. I know that some of my pen are in the touring cases of a few musicians, one of which is in the rock and roll hall of fame. But I have to keep it tight!

Before leaving to work for myself, I was part of a design team at IDEO in Cambridge that designed the new Simplisafe Home Security System. As an engineer and designer, I got listed on the patents. That wasn’t machining and was more design and engineering of injection molded plastic assemblies,  but it was still cool, though! Cutting my teeth in the design industry before machining helps me a lot with the creative process in the workshop. Lots of overlap.

What capabilities does your shop have?

I utilize Citizen L series sliding headstock machines to run my company. These are Swiss Machines (though made in Japan) with twin spindles and have live tooling for milling operations. I got into this type of machining after getting advice from friends in the industry and subcontracting my work to shops with these style of machines for 7 years.

Beyond the Swiss Machines, I have a new Precision Matthews Manual Mill, a Southbend Model A, a Hardinge Cataract Lathe, and a bunch of smaller Derbyshire lathes and mills. Most of these are for maintenance related tasks – quick mods and fixtures and my watchmaking/R&D stuff. I also have a Bantam Tools Desktop CNC machine on the way, a nice machine for quick milled fixtures in aluminum and nonferrous materials. I tested this machine during their development phases and was really impressed.

What CAM/CAD software are you using?

I use Fusion 360 for quick milled stuff, but most of my parts are programmed by hand since the lathe programming for Swiss work can be done without much CAM. I’m sure I could be doing things better on the programming side, but hey, every day I learn something new. Who knows what I’ll be doing a year or two from now?

schon dsgn turning wrist watch on lathe

What is your favorite material to work with and why?

Brass and Copper. The chips aren’t stringy, it’s easy to cut quickly and the parts have this nice hefty feel to them. Since I make pens, the weight is a big piece of the feeling of a pen. The only downside is I’m constantly figuring out ways to not dent the parts as they are coming off the machines! My brass parts are like tiny brass mallets and they LOVE to get dinged up in the ejection cycles. I ended up making custom parts catchers and modifying the chutes on the machines to navigate this. I might have some conveyors in my future….yeah. Too many projects!

schon dsgn disassembled wrist watch

Why is high quality tool performance important to you?

It’s not just important, it’s SUPER important. As a solo machinist running my own machines, being able to call a tooling company and get answers on how I should run a tool, adjust its RPM, feed, DOC, or cutting strategy to get a better result is invaluable. I find that as much as I’m paying for tool performance, I’m also paying for expertise, wisdom and answers. Knowing everything is cool and all (and I know some of you out there know everything under the sun), but since I don’t know everything, it’s so nice to be able to pick up a phone and have someone in my corner. These tech support people are so crucial. Being humble and letting support guide me through my tooling challenges has helped me grow a lot. It’s like having a staff of experienced machinists working at my company, for free! Can’t beat that. Micro 100 and Helical have helped me tons with their great support.

schon dsgn multicolored fountain pens

When was a time that Harvey, Helical or Micro product really came through and helped your business?

The Helical team (shout out to Dalton) helped me nail some machining on some very wild faceted pens I was working on this month. When I switched to Helical, my finishes got crazy good. I just listened to recommendations, bought a bunch of stuff, and kept trying what Dalton told me to. Eventually, that led to a good recipe and manageable tool wear. It was great!

I also like how representatives from the Harvey/Helical/Micro family often cross reference each other and help me find the right solution, regardless of which company I’m getting it from. Nice system.

The quiet hero in my shop is my Micro 100 quick change system. It just works great. Fast to swap tools, easy to setup, cannot argue with it! Too good. 

Schon DSGN silver wrist watch with black band

If you could give one piece of advice to a new machinist ready to take the #PlungeIntoMachining, what would it be?

Find a mentor who supports you and challenges you. Find a good tooling company, or good tooling companies, and make good relationships with their tech support so you can get answers. Make good relationships with service technicians who can help you fix your machines. Be a good person. Don’t let yourself become a hot head under the pressure of this industry (since it can be hard at times!), cooler heads prevail, always. Be open to seeing things from other viewpoints (in life and in machining), don’t be afraid to flip a part around and start over from square one.

To learn more about Ian and Schon DSGN, follow them @schon_dsgn and @the_schon on Instagram and check out his website. And, to learn more about how Ian got his start in the manufacturing industry, check out this video.

Successful Slotting With Miniature Cutting Tools

Whether your tool is a 1” diameter powerhouse rougher or a .032” precision end mill, slotting is one of the hardest operations on the tool. During slotting operations, a lot of force and pressure is placed on the entire cutting edge of the tool. This results in slower speeds and feeds and increased tool wear, making it one of the nastier processes even for the best cutting tools.

With miniature tooling (for the purposes of this blog, under 1/8” diameter) the game changes. The way we approach miniature tooling is completely different as it relates to slotting. In these instances, it is vitally important to select the correct tool for these operations. A few of the suggestions may surprise you if you are used to working with larger tooling, but rest assured, these are tried and tested recommendations which will dramatically increase your success rate in miniature slotting applications.

Use as Many Flutes as Possible

When running traditional slotting toolpaths, the biggest concern with the cutting tool is getting the best chip evacuation by using the proper flute count. Traditionally speaking, you want to use the fewest amount of flutes possible. In Aluminum/Non-Ferrous jobs, this is typically no more than 2/3 flutes, and in Steel/Ferrous applications, 4 flutes is recommended. The lower flute count leaves room for the chips to evacuate so you are not re-cutting chips and clogging the flutes on your tool in deep slots.

When slotting with miniature tools, the biggest concerns are with tool rigidity, deflection, and core strength. With micro-slotting we are not “slotting”, but rather we are “making a slot”. In traditional slotting, we may drive a ½” tool down 2xD into the part to make a full slot, and the tool can handle it! But this technique simply isn’t possible with a smaller tool.

graphic showing difference between core sizes on 3 flute and 5 flute slotting tools

For example, let’s take a .015” end mill. If we are making a slot that is .015” deep with that tool, we are likely going to take a .001” to .002” axial depth per pass. In this case, chips are no longer your problem since it is not a traditional slotting toolpath. Rigidity and core strength are now key, which means we need to add as many flutes as possible! Even in materials like Aluminum, 4 or 5 flutes will be a much better option at smaller diameters than traditional 2/3 flute tools. By choosing a tool with a higher flute count, some end users have seen their tool life increase upwards of 50 to 100 times over tools with lower flute counts and less rigidity and strength.

Use the Strongest Corner Possible When Slotting

Outside of making sure you have a strong core on your miniature tools while making a slot, you also need to take a hard look at your corner strength. Putting a corner radius on your tooling is a great step and does improve the corner strength of the tool considerably over a square profile tool. However, if we want the strongest tip geometry, using a ball nose end mill should also be considered.

A ball nose end mill will give you the strongest possible tip of the three most common profiles. The end geometry on the ball nose can almost work as a high feed end mill, allowing for faster feed rates on the light axial passes that are required for micro-slotting. The lead angle on the ball nose also allows for axial chip thinning, which will give you better tool life and allow you to decrease your cycle times.

.078
A .078″ ball nose end mill was used for this miniature slotting operation

Finding the Right Tool for Miniature Slotting Operations

Precision and accuracy are paramount when it comes to miniature tooling, regardless of whether you are slotting, roughing, or even simply looking to make a hole in a part. With the guidelines above, it is also important to have a variety of tooling options available to cater to your specific slotting needs. Harvey Tool offers 5 flute end mills down to .015” in diameter, which are a great option for a stronger tool with a high flute count for slotting operations.

miniature .010
Harvey Tool offers many miniature end mill options, like the .010″ long reach end mill above.

If you are looking to upgrade your corner strength, Harvey Tool also offers a wide selection of miniature end mills in corner radius and ball nose profiles, with dozens of reach, length of cut, and flute count options. Speeds and feeds information for all of these tools is also available, making your programming of these difficult toolpaths just a little bit easier.

Conclusion

To wrap things up, there are three major items to focus on when it comes to miniature slotting: flute count, corner strength, and the depth of your axial passes.

It is vital to ensure you are using a corner radius or ball nose tool and putting as many flutes as you can on your tool when possible. This keeps the tool rigid and avoids deflection while providing superior core strength.

For your axial passes, take light passes with multiple stepdowns. Working your tool almost as a high feed end mill will make for a successful slotting operation, even at the most minuscule diameters.

How to Optimize Results While Machining With Miniature End Mills

 The machining industry generally considers micromachining and miniature end mills to be any end mill with a diameter under 1/8 of an inch. This is also often the point where tolerances must be held to a tighter window. Because the diameter of a tool is directly related to the strength of a tool, miniature end mills are considerably weaker than their larger counterparts, and therefore, lack of strength must be accounted for when micromachining. If you are using these tools in a repetitive application, then optimization of this process is key.

Key Cutting Differences between Conventional and Miniature End Mills

Runout

Runout during an operation has a much greater effect on miniature tools, as even a very small amount can have a large impact on the tool engagement and cutting forces. Runout causes the cutting forces to increase due to the uneven engagement of the flutes, prompting some flutes to wear faster than others in conventional tools, and breakage in miniature tools. Tool vibration also impacts the tool life, as the intermittent impacts can cause the tool to chip or, in the case of miniature tools, break. It is extremely important to check the runout of a setup before starting an operation. The example below demonstrates how much of a difference .001” of runout is between a .500” diameter tool and a .031” diameter tool.

chart comparing tool diameter for runout in micromachining
The runout of an operation should not exceed 2% of the tool diameter. Excess runout will lead to a poor surface finish.

Chip Thickness

The ratio between the chip thickness and the edge radius (the edge prep) is much smaller for miniature tools. This phenomena is sometimes called “the size effect” and often leads to an error in the prediction of cutting forces. When the chip thickness-to-edge radius ratio is smaller, the cutter will be more or less ploughing the material rather than shearing it. This ploughing effect is essentially due to the negative rake angle created by the edge radius when cutting a chip with a small thickness.

If this thickness is less than a certain value (this value depends of the tool being used), the material will squeeze underneath the tool. Once the tool passes and there is no chip formation, part of the plowed material recovers elastically. This elastic recovery causes there to be higher cutting forces and friction due to the increased contact area between the tool and the workpiece. These two factors ultimately lead to a greater amount of tool wear and surface roughness.

chart of edge radius in relation to chip thickness for micromachining
Figure 1: (A) Miniature tool operation where the edge radius is greater than the chip thickness (B) Conventional operation where the edge radius is small than the chip thickness

Tool Deflection in Conventional vs. Micromachining Applications

Tool deflection has a much greater impact on the formation of chips and accuracy of the operation in micromachining operations, when compared to conventional operations. Cutting forces concentrated on the side of the tool cause it to bend in the direction opposite the feed. The magnitude of this deflection depends upon the rigidity of the tool and its distance extended from the spindle. Small diameter tools are inherently less stiff compared to larger diameter tools because they have much less material holding them in place during the operation. In theory, doubling the length sticking out of the holder will result in 8 times more deflection. Doubling the diameter of an end mill it will result in 16 times less deflection. If a miniature cutting tool breaks on the first pass, it is most likely due to the deflection force overcoming the strength of the carbide. Here are some ways you can minimize tool deflection.

Workpiece Homogeny

Workpiece homogeny becomes a questionable factor with decreasing tool diameter. This means that a material may not have uniform properties at an exceptionally small scale due to a number of factors, such as container surfaces, insoluble impurities, grain boundaries, and dislocations. This assumption is generally saved for tools that have a cutter diameter below .020”, as the cutting system needs to be extremely small in order for the homogeny of the microstructure of the material to be called into question.

Surface Finish

Micromachining may result in an increased amount of burrs and surface roughness when compared to conventional machining. In milling, burring increases as feed increases, and decreases as speed increases. During a machining operation, chips are created by the compression and shearing of the workpiece material along the primary shear zone. This shear zone can be seen in Figure 2 below. As stated before, the chip thickness-to-edge radius ratio is much higher in miniature applications. Therefore, plastic and elastic deformation zones are created during cutting and are located adjacent to the primary shear zone (Figure 2a). Consequently, when the cutting edge is close to the border of the workpiece, the elastic zone also reaches this border (Figure 2b). Plastic deformation spreads into this area as the cutting edge advances, and more plastic deformation forms at the border due to the connecting elastic deformation zones (Figure 2c). A permanent burr begins to form when the plastic deformation zones connect (Figure 2d) and are expanded once a chip cracks along the slip line (Figure 2e). When the chips finally break off from the edge of the workpiece, a burr is left behind (Figure 2f).

Tool Path Best Practices for Miniature End Mills

Because of the fragility of miniature tools, the tool path must be programmed in such a way as to avoid a sudden amount of cutting force, as well as permit the distribution of cutting forces along multiple axes. For these reasons, the following practices should be considered when writing a program for a miniature tool path:

Ramping Into a Part

Circular ramping is the best practice for moving down axially into a part, as it evenly distributes cutting forces along the x, y, and z planes. If you have to move into a part radially at a certain depth of cut, consider an arching tool path as this gradually loads cutting forces onto the tool instead of all at once.

Micromachining in Circular Paths

You should not use the same speeds and feed for a circular path as you would for a linear path. This is because of an effect called compounded angular velocity. Each tooth on a cutting tool has its own angular velocity when it is active in the spindle. When a circular tool path is used, another angular velocity component is added to the system and, therefore, the teeth on the outer portion of tool path are traveling at a substantially different speed than expected. The feed of the tool must be adjusted depending on whether it is an internal or external circular operation. To find out how to adjust your feed, check out this article on running in circles.

Slotting with a Miniature Tool

Do not approach a miniature slot the same way as you would a larger slot. With a miniature slot, you want as many flutes on the tool as possible, as this increases the rigidity of the tool through a larger core. This decreases the possibility of the tool breaking due to deflection. Because there is less room for chips to evacuate with a higher number of flutes, the axial engagement must be decreased. With larger diameter tools you may be stepping down 50% – 100% of the tool diameter. But when using miniature end mills with a higher flute count, only step down between 5% – 15%, depending on the size of the diameter and risk of deflection. The feed rate should be increased to compensate for the decreased axial engagement. The feed can be increased even high when using a ball nose end mill as chip thinning occurs at these light depths of cut and begins to act like a high feed mill.

Slowing Down Your Feed Around Corners

Corners of a part create an additional amount of cutting forces as more of the tool becomes engaged with the part. For this reason it is beneficial to slow down your feed when machining around corners to gradually introduce the tool to these forces.

Climb Milling vs. Conventional Milling in Micromachining Applications

This is somewhat of a tricky question to answer when it comes to micromachining. Climb milling should be utilized whenever a quality surface finish is called for on the part print. This type of tool path ultimately leads to more predictable/lower cutting forces and therefore higher quality surface finish. In climb milling, the cutter engages the maximum chip thickness at the beginning of the cut, giving it a tendency to push away from the workpiece. This can potentially cause chatter issues if the setup does not have enough rigidity.  In conventional milling, as the cutter rotates back into the cut it pulls itself into the material and increases cutting forces. Conventional milling should be utilized for parts with long thin walls as well as delicate operations.

Combined Roughing and Finishing Operations

These operations should be considered when micromachining tall thin walled parts as in some cases there is not sufficient support for the part for a finishing pass.

Helpful Tips for Achieving Successful Micromachining Operations

Try to minimize runout and deflection as much as possible when micromachining. This can be achieved by using a shrink-fit or press-fit tool holder. Maximize the amount of shank contact with the collet while minimizing the amount of stick-out during an operation. Double check your print and make sure that you have the largest possible end mill because bigger tools mean less deflection.

  • Choose an appropriate depth of cut so that the chip thickness to edge radius ratio is not too small as this will cause a ploughing effect.
  • If possible, test the hardness of the workpiece before machining to confirm the mechanical properties of the material advertised by the vender. This gives the operator an idea of the quality of the material.
  • Use a coated tool if possible when working in ferrous materials due to the excess amount of heat that is generated when machining these types of metals. Tool coatings can increase tool life between 30%-200% and allows for higher speeds, which is key in micro-machining.
  • Consider using a support material to control the advent of burrs during a micromachining application. The support material is deposited on the workpiece surface to provide auxiliary support force as well as increase the stiffness of the original edge of the workpiece. During the operation, the support material burrs and is plastically deformed rather than the workpiece.
  • Use flood coolant to lower cutting forces and a greater surface finish.
  • Scrutinize the tool path that is to be applied as a few adjustments can go a long way in extending the life of a miniature tool.
  • Double-check tool geometry to make sure it is appropriate for the material you are machining. When available, use variable pitch and variable helix tools as this will reduce harmonics at the exceptionally high RPMs that miniature tools are typically run at.
variable pitch versus non-variable pitch
Figure 3: Variable pitch tool (yellow) vs. a non-variable pitch tool (black)

TOMI Engineering INC – Featured Customer

Since its beginning in 1977, brothers Tony and Mike Falbo have made the focal point of TOMI Engineering to deliver quality, competitively-priced parts on time. TOMI Engineering has earned a reputation through the years as being a world-class manufacturer of precision machined components and assemblies for aerospace, defense, commercial and other advanced technology industries. They are fortunate to have the highest level of engineering, quality and programming personnel on staff, and, with over 40 years in the industry, there isn’t a problem TOMI hasn’t experienced.

With all the years of experience, TOMI Engineering has a lot of knowledge to share. We had the pleasure of sitting down with Tony and Mike Falbo to ask them about their experiences, techniques, tooling and a lot more.

green machined part from Tomi Engineering INC

How was TOMI Engineering INC started?

TOMI Engineering, Inc. began in 1977 when we (Tony and Mike) teamed up and got a loan from our father to purchase our first machine.  The machine was used in the garage of our parents’ home, which still resides in Tustin, California.  Forty years, 20 current machines, and countless parts later, TOMI Engineering proudly serves the defense, airline, medical and commercial industries.  We machine just about any type of product thrown our way.  Over the years, we have made wing tips for the F16 fighter jet, enclosures for GPS housings, manifolds that help transport fluids, support frames for Gulfstream, cabin brackets for Airbus, ammunition feeders for tanks, and many, many others.

At TOMI Engineering, we aim to be a one-stop shop for our customers.  Once we receive blueprints, we can program, machine, deburr, inspect, process and assemble most parts.  We utilize a mixture of 3-and-4-axis machines in order to increase efficiency, which helps us to cut down costs to our customer.  In our temperature-controlled assembly room, we can assemble bearings, bushings, rivets, nut plates, gaskets and sealants.  We also hope to add additive machining to our repertoire soon.

What machines are you currently using in your shop?

Our 21,250 square foot facility houses 20 CNC machines.  Most of our machines are Kitamura, OKK and Okuma.  The purchase dates of these machines range from 1987 to December of 2019.  With our large machine diversity, we can machine parts smaller than a penny, and as large as 30 x 60 inches. Most of the material that makes its way through our shop is aluminum.  Whether it is 6061 or aircraft grade 7000 series, we aim to have most of our parts be aluminum.  However, we do see a large amount of 6AL-4V titanium, along with 17-4 and 15-5 steel. We are currently utilizing Mastercam 2020 for most of our programming needs and are staying up to date with software upgrades and progression.

Tomi Engineering CNC mill

What sets TOMI Engineering apart from the rest of the competition?

We believe our greatest asset is our experience.  Here at TOMI, we have been machining parts since 1977.  In those 40-plus years, a lot of parts have come and gone through our doors and we have helped our customers solve a large array of problems.  Most of our machinists have been with us for over 10 years, while some are approaching 20 years!  Our programmers easily boast over 60 years of experience! With so many of our employees working together for so many years, it has really helped everyone to understand what helps us quickly machine our products, while being held accountable to the high standards of AS9100. 

Where did your passion for machining start?

We grew up with machines in our garage and it wasn’t until we needed money to pay for college that our dad realized he could show us the basics of operating a milling machine, which allowed us to pay our tuition while working at home in the evenings and weekends. Machining was more of a necessity than a passion at the time. However, after nearly 40 years in the business, it has been amazing to see the strides in technology from a Bridgeport Mill to the multi-axis lights-out machining that is available today.

My favorite part of the job has always been the flexibility it has allowed me. I had the opportunity to watch my kids grow up and be a part of their lives by going to their school plays, coaching them, and being home at night to help them with anything they needed. Most importantly, I’ve had the opportunity to work with my brother, my business partner, who also shares the same ideals about being with family, so we could always cover for each while the other was gone and spending time with their family. The business would not have worked without both of us understanding the importance of each other’s input. The challenge of running a business keeps me going, and working with all of the different personalities was an added bonus.

machined part from Tomi Engineering

Who is the most famous contact that you have worked on a project with? What is the most interesting product youve made?

At TOMI, we do not work with specific individuals, so we can’t really name drop.  However, a vast majority of our work is for Airbus, Boeing, or the military. So it’s pretty gratifying to say that we supply parts to some of the biggest companies in the world and that our work helps to defend this country.

The most interesting product we have made here at TOMI is a GPS housing for a defense contractor.  This part encompasses everything that we can do at TOMI: precision machining, complex/multi detail assemblies, gasket assembly, and pressure testing fluid transportation components. 

Why is high quality tool performance important to you?

High quality tool performance is important to us in many ways.  Purchasing high quality tools allow us to constantly achieve premium surface finishes, push our machines to the high speeds and feeds that they are capable of, and enjoy noticeably longer tool life.

Every part, day-in and day-out, is different.   Because of our vast array of products, our tools are always changing.  But when we are picking out Helical End Mills for Aluminum, we always go with their 3-flute variable helix cutters, and we have always been happy with them.

machined part from Tomi Engineering

What sort of tolerances do you work in on a daily basis?

The tolerances we typically work with are ± tenths of an inch, as well as very tight true position cal louts. We can hold and achieve these close tolerance dimensions through our very experienced Mastercam programmers, as well as our superior quality department.  Our quality inspectors have over 30 years of experience in the industry and utilize two Zeiss Contura G2 coordinate measuring machines (CMMs).  While in their temperature controlled environment, the CMMs are capable of measuring close tolerance dimensions and are used to generate data for inspection reports.

Are you guys using High Efficiency Milling (HEM) techniques to improve cycle times? What advice do you have for others who want to try HEM?

Yes, we are using HEM techniques to improve cycle times while roughing to increase our MRR while increasing tool life. If you have CAM/CAD software that supports HEM, then go for it!  Machining Advisor Pro (MAP) is VERY helpful with the suggested speeds and feeds as a starting point.  Over time though, and through experience, we have learned that every single machine is a bit different and often needs a different approach with speeds and feeds.  Start with a smaller than suggested RDOC and physically go out to your machine and see how it sounds and what is going on.  Then, start increasing and find that sweet spot that your particular machine runs well on.  Many programmers in the industry will not take the time to go out and watch how their part is sounding and cutting on the machine and going out and doing that is the best way to really find out what you and the machine are capable of achieving.

If you could give one piece of advice to a new machinist ready to take the #PlungeIntoMachining, what would it be?

Ask questions!  Don’t be afraid to talk to programmers and fellow coworkers about what is trying to be achieved and WHY the programmer is holding tolerances a certain way.  Learn from them and watch what every cutter is doing during your cycles.  The more you learn, the more you can contribute to the machining process and move up in your business.  Sometimes it takes just one good suggestion about the machining approach that can change the set-up process from aggravating to very easy.  Lastly, be open minded to new ideas and approaches.  As we said earlier, there are a ton of ways to make good parts in a constantly evolving industry.

Please take the time to check out the TOMI Engineering INC website or follow them on social media!

Titan Ring Design – Featured Customer

Officially started in 2015, Titan Ring Design is a high quality machine shop that designs rings, as well as mechanical tie clips, art based designs, and freelance custom designs. While working at a machine shop that produced top notch parts for just about every type of field you can imagine, now owner of Titan Ring Design, Trevor Hirschi, noticed that the machining industry is mostly about cranking out a mass quantity of the highest quality parts as quickly as possible. This often resulted in compromised tolerances and part finishes, something Trevor aimed to change. Quality always comes first in his projects.

Whether you are looking for a band for an upcoming wedding, looking to replace or upgrade your current wedding ring, or just want something unique and beautiful, Trevor’s designs are different than anything else. Trevor was able to take the time and answer some questions for us about his business, machining techniques, tooling, and a lot more.

machined metal ring from Titan Ring Design

How was Titan Ring Design started?

Titan Ring Designs is a part time, passion/hobby business of mine that I sort of started at the time I was ring shopping for a wedding ring back in 2013. I didn’t like what was available on the market and was inspired by a former Oakley designer to machine my own. I had been introduced to machining in High School at a technical college and had been working as a machinist since graduating in 2007, so I decided to make my own wedding ring. It sort of snowballed into my business in 2015, after finally deciding to make it official with a business license and some sales. Some further work experience in California for McWhinney Designs brought me greater motivation and encouragement to keep going and helped me get to where I am today. I now offer several different CNC Milled [wedding] rings, as well as a mechanical tie clip, some occasional art based designs, and freelance custom design and mill work. I also teach machining full time  at the same tech college I graduated from in my own education and enjoy sharing my knowledge and love for machining with those interested in the career.

machined propeller art from Titan Ring Design

What capabilities does your shop have?

Custom Design in CAD/CAM, 3axis CNC Mill work, Small Scale Lathe Work, Tumbling, Finishing, Assembling, 3D Printing/Rapid Prototyping. I cut 6-4 Titanium primarily, but also work with Stainless Steel for fasteners, Aluminum and some Steel for fixtures, and Polycarbonate for prototyping ideas. I teach machining technology full time, so I have access to SolidWorks, MasterCam, Fusion360, and NC Simul. We currently have a Haas OfficeMill 3axis, Levin High Precision Instrument Maker’s Lathe, Prusa i3 MK2S 3D Printer in the shop.

What sets Titan Ring Design apart from the competition?

There are lots of people making interesting rings today, but most are done on lathes. Anyone can make a round part on a lathe. Very few of them make rings on a mill, and I feel that gives the opportunity to be creative and allows you to think outside the box more. I try to stand out in that field by offering something that makes you think about the value of the design process more by interrupting and challenging the norm. I also like to take on work that is outside of jewelry, but still highly design related. Most other ring makers stick with just rings.

Titan Ring Design machining facility

What is your favorite part of the job and what other passions do you have?

Making cool stuff! Most machinists only end up making whatever comes through the shop, which can be cool, but most of the time you have no idea what you’re making, just some part for Customer X, Y, or Z. Being a small, design centered business, I get to come up with ideas for what to make next, and most of the time I start out making something that wasn’t ever intended to be marketed, it was simply something I wanted for myself that I found others were interested in too. I discovered machining in high school and fell in love with it when I started making parts for my dirt bikes and truck. I’ve been hooked ever since but I do have other passions. I’ve always had a big interest in LED lighting and flashlights. I’m perpetually working on different ideas for making one of my own, which will happen eventually. I’m also a bit of a health-nut and enjoy being outdoors and spending time with my family.

Who is the most famous contact that you have worked on a project with?

I made a ring for an NFL player once, but I don’t follow football and his name didn’t stick out to me so I’ve forgotten who he was. I also had the privilege of working for McWhinney Designs and made some truly remarkable products in the openable wedding ring niche market. I gained more skill in design, machining, craftsmanship, and engineering while working for Jeff McWhinney. We’re good friends and often work together to help each other when one of us gets stumped on something.

machined metal art from Titan Ring Design

What is the most difficult project you have worked on?

I was commissioned to design from the ground up and machine was a custom set of all-titanium cabinet door handle pulls for a very high end wine cabinet. Each handle was an assembly of 32 pieces, all machined from billet 6-4 Titanium. They required over 400 individual CAM toolpath operations, 35 unique machine setups, and well over 300 hours to complete, including finishing and assembly. More than anything, it was extremely time intensive in programming, set up, and machine time. The design was a fair bit challenging in my mind and initial modeling, but didn’t compete with what it took to actually produce them. I grossly underestimated and underbid the job. But in the end, I really enjoyed making a truly one of a kind, Tour-De-Force product, even if it was completely overkill for its purpose. I enjoy making that kind of stuff, and the lessons you learn from it.

What is your favorite project you have worked on?

It’s really simple and was initially designed just because I wanted it for myself, but I have a mechanical titanium tie clip that I really enjoy making. It’s quite unique in that, as far as I know, to this day, it is the only CNC machined mechanical titanium tie clip you’ll find anywhere in the world. It puts a little bling in your formal attire, for those times you have to go full suit and tie.

machined metal band from Titan Ring Design

Why is high quality tool performance important to you?

Because I cut mostly titanium, tools wear out quickly if you don’t have a rigid set up, the right coolant, proper feeds & speeds, and of course, high quality tooling. Harvey Tool makes such a wide variety of micro tooling that works so well in the industry of making small titanium parts, where I like to fit into. I’ve used a fair spread across Harvey’s offering and have always been impressed with performance and the feeds and speeds guides are top notch too. I had an application that required a .0035” internal corner radius which landed me with a .007” end mill. It’s still hard to comprehend tooling in this league. My machine actually recommends only tooling under 1/4” shank size, so I don’t get into Helical’s range too often. But I’ve used Helical 1/2” end mills extensively at other job shops and they are definitely made for eating metal. I was using another tool brand’s key cutters for some undercut hinges and would wear through them much more often than I thought was reasonable. When I finally decided to try Harvey’s key cutters, I was blown away with how much longer they have lasted me. Truly a game changer!

harvey tool end mills with Titan Ring Design machined tie clip

If you could give one piece of advice to a new machinist ready to take the #PlungeIntoMachining, what would it be?

Be creative. Machining is such a rewarding career that has limitless possibilities of what you can achieve. Follow your passion and have fun with it! If you end up in a dead end shop doing something you don’t like, go somewhere else. There are so many shops that need help right now and chances are good that you can find a better shop that suits your style.

Is there anything else you would like to share with the In The Loupe community?

To those machine shops out in industry, do whatever you can to be supportive of your local trade schools that are teaching the upcoming machinist workforce. They really need your support and in turn will bring you the employees you depend on.

Please take the time to check out Titan Ring Designs website or follow them on Instagram @titanringdesigns

Chipbreaker Tooling: Not Just for Roughing

When many people think about solid carbide tools with chip breakers, they are usually tooling up for a roughing application. While the chip breaker tool is a great choice for such applications, it can be utilized in a number of other areas too. In this post, we’ll examine many other benefits of the chip breaker style of tooling.

https://www.instagram.com/p/B7JqOQKnoPu/

High Efficiency Milling (HEM)

High Efficiency Milling (HEM) uses CAM software to program advanced toolpaths that reduce cutting forces. These tool paths employ smaller end mills with a higher number of flutes (for a stronger core) running at higher speeds and feeds. This strategy includes a light radial depth of cut (RDOC), high axial depth of cut (ADOC), and a controlled angle of engagement.

Helical’s chipbreaking tools include serrated indents along the edge of flute for the entire length of cut. Because HEM utilizes heavy axial depths of cuts, these tools are able to break long chips into smaller ones. In addition to improving chip control and reducing cutting resistance, chipbreaker tools also help in decreasing heat load within the chips. This delays tool wear along the cutting edge and improves cutting performance. 

Check out this testimony from a Helical Solutions customer:

“We were able to get going with the 7 flute tools with the chipbreaker. I have to say the difference was INCREDIBLE! We can now rough the entire part with one tool. Also, the operator doesn’t have to open the door to clear chips hardly at all. We were able to rough and finish a 4.15 dia. bore 2 inches deep through the part without having to clear chips at all. Before we had to clear the chips out at least 15-20 times. Many thanks for your support.”

Slotting

When slotting, a major concern is chip control. A large buildup of chips can cause the recutting of chips, which adds a lot of heat back into the tool. Chip buildup can also cause a heavy amount of chattering. Both of these conditions are detrimental to tool life. A chip breaking tool can help reduce chip build-up when slotting which will extend tool life. Remember when slotting that 4 flute tools should be utilized in steel. For aluminum and other non- ferrous materials, a 3 flute tool is best.

Trochoidal Slotting

Trochoidal slotting is a form of slotting that uses HEM techniques to form a slot. Trochoidal milling implements a series of circular cuts to create a slot wider than the cutting tool’s cutting diameter. Using the logic listed in the earlier paragraphs of this article, a chipbreaker should be used when performing this operation.

Advantages of Trochoidal Slotting:

Decreased cutting forces

Reduced heat

Greater machining accuracy

Improved tool life

Faster cycle times

One tool for multiple slot sizes

Finishing

A little known fact about Helical’s chipbreaker style tool is that the chip breakers are offset flute to flute, which allows for a quality finish on the walls of the part. When utilizing light depths of cuts, high-quality finishes can be achieved.

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Hardenability of Steel

Many types of steel have a beneficial response to a method of heat treatment known as quenching. One of the most important criteria in the selection process of a workpiece material is hardenability. Hardenability describes how deep a metal can be hardened upon quenching from high temperature, and can also be referred to as the depth of hardening.

Steel At Microscopic Scale:

The first level of classification of steels at a microscopic level is their crystal structure, the way in which atoms are arranged in space. Body-Centered Cubic (BCC) and Face Centered Cubic (FCC) configurations are examples of metallic crystal structures. Examples of BCC and FCC crystal structures can be seen below in Figure 1. Keep in mind that the images in Figure 1 are meant to display atomic position and that the distance between the atoms is exaggerated.

depiction of BBC and FCC crystal structures in steel
Figure 1: Example of a BCC crystal structure (left) and FCC crystal structure (right)

The next level of classification is a phase. A phase is a uniform portion of a material that has the same physical and chemical properties. Steel has 3 different phases:

  1. Austenite: Face-Centered cubic iron; also iron and steel alloys that have the FCC crystal structure.
  2. Ferrite: Body-centered cubic iron and steel alloys that have a BCC crystal structure.
  3. Cementite: Iron carbide (Fe3C)

The final level of classification discussed in this article is the microstructure. The three phases seen above can be combined to form different microstructures of steel. Examples of these microstructures and their general mechanical properties are shown below:

  • Martensite: the hardest and strongest microstructure, yet the most brittle
  • Pearlite: Hard, strong, and ductile but not particularly tough
  • Bainite: has desirable strength-ductility combination, harder than pearlite but not as hard as martensite

Hardening at Microscopic Scale:

The hardenability of steel is a function of the carbon content of the material, other alloying elements, and the grain size of the austenite. Austenite is a gamma phase iron and at high temperatures its atomic structure undergoes a transition from a BCC configuration to an FCC configuration.

High hardenability refers to the ability of the alloy to produce a high martensite percentage throughout the body of the material upon quenching. Hardened steels are created by rapidly quenching the material from a high temperature. This involves a rapid transition from a state of 100% austenite to a high percentage of martensite. If the steel is more than 0.15% carbon, the martensite becomes a highly strained body-centered cubic form and is supersaturated with carbon. The carbon effectively shuts down most slip planes within the microstructure, creating a very hard and brittle material. If the quenching rate is not fast enough, carbon will diffuse out of the austenitic phase. The steel then becomes pearlite, bainite, or if kept hot long enough, ferrite. None of the microstructures just stated have the same strength as martensite after tempering and are generally seen as unfavorable for most applications.

The successful heat treatment of a steel depends on three factors:

  1. The size and shape of the specimen
  2. The composition of the steel
  3. The method of quenching

1. The size and shape of the specimen

During the quenching process, heat must be transferred to the surface of the specimen before it can be dissipated into the quenching medium. Consequently, the rate at which the interior of the specimen cools is dependent on its surface area to volume ratio. The larger the ratio, the more rapid the specimen will cool and therefore the deeper the hardening effect. For example, a 3-inch cylindrical bar with a 1-inch diameter will have a higher hardenability than a 3-inch bar with a 1.5-inch diameter. Because of this effect, parts with more corners and edges are more amendable to hardening by quenching than regular and rounded shapes. Figure 2 is a sample time-temperature transformation (TTT) diagram of the cooling curves of an oil-quenched 95 mm bar. The surface will transform into 100% martensite while the core will contain some bainite and thus have a lower hardness.

graph of sample time temperature transformation
Figure 2: Sample time temperature transformation (TTT) diagram also known as an isothermal transformation diagram

2.  The composition of the steel

It’s important to remember that different alloys of steel contain different elemental compositions. The ratio of these elements relative to the amount of iron within the steel yield a wide variety of mechanical properties. Increasing the carbon content makes steel harder and stronger but less ductile. The predominant alloying element of stainless steels in chromium, which gives the metal its strong resistance to corrosion. Since humans have been tinkering with the composition of steel for over a millennium, the number of combinations is endless.

Because there are so many combinations that yield so many different mechanical properties, standardized tests are used to help categorize different types of steel. A common test for hardenability is the Jominy Test, shown in Figure 3 below. During this test a standard block of material is heated until it is 100% austenite. The block is then quickly moved to an apparatus where it is water quenched. The surface, or the area in contact with the water, is immediately cooled and the rate of cooling drops as a function of distance from the surface. A flat is then ground onto the block along the length of the sample. The hardness at various points is measured along this flat. This data is then plotted in a hardenability chart with hardness as the y-axis and distance as the x-axis.

diagram of Jominy end quench specimen for hardened steel
Figure 3: Diagram of a Jominy end quench specimen mounted during quenching (left) and post hardness testing (right)

Hardenability curves are constructed from the results of Jominy Tests. Examples of a few steel alloy curves are shown in Figure 4. With a diminishing cooling rate (steeper drop in hardness over a short distance), more time is allowed for carbon diffusion and the formation of a greater proportion of softer pearlite. This means less martensite and a lower hardenability. A material that retains higher hardness values over relatively long distances is considered highly hardenable. Also, the greater the difference in hardness between the two ends, the lower the hardenability. It is typical of hardenability curves that as the distance from the quenched end increases, the cooling rate decreases. 1040 steel initially has the same hardness as both 4140 and 4340 but cools extremely quickly over the length of the sample. 4140 and 4340 steel cool at a more gradual rate and therefore have a higher hardenability. 4340 has a less extreme rate of coolness relative to 4140 and thus has the highest hardenability of the trio.

chart of hardenability for 4140, 1040, and 4340 steel
Figure 4: Hardenability charts for 4140, 1040 and 4340 steels

Hardenability curves are dependent on carbon content. A greater percentage of carbon present in steel will increase its hardness. It should be noted that all three alloys in Figure 4 contain the same amount of carbon (0.40% C).  Carbon is not the only alloying element that can have an effect on hardenability. The disparity in hardenability behavior between these three steels can be explained in terms of their alloying elements. Table 1 below shows a comparison of the alloying content in each of the steels. 1040 is a plain carbon steel and therefore has the lowest hardenability as there are no other elements besides iron to block the carbon atoms from escaping the matrix. The nickel added to 4340 allows for a slightly greater amount of martensite to form compared to 4140, giving it the highest hardenability of these three alloys. Most metallic alloying elements slow down the formation of pearlite, ferrite and bainite, therefore they increase a steel’s hardenability.

Table 1: Shows the alloying contents of 4340, 4140, and 1040 steel

Type of Steel: Nickel (wt %): Molybdenum (wt %): Chromium (wt %):
4340 1.85% 0.25% 0.80%
4140 0.00% 0.20% 1.00%
1040 0.00% 0.00% 0.00%

There can be a variation in hardenability within one material group. During the industrial production of steel, there are always slight unavoidable variations in the elemental composition and average grain size from one batch to another. Most of the time a material’s hardenability is represented by maximum and minimum curves set as limits.

Hardenability also increases with increasing austenitic grain size. A grain is an individual crystal in a polycrystalline metal. Think of a stained glass window (like the one seen below), the colored glass would be the grains while the soldering material holding it altogether would be the grain boundaries. Austenite, ferrite, and cementite are all different types of grains that make up the different microstructures of steel. It is at the grain boundaries that the pearlite and bainite will form. This is detrimental to the hardening process as martensite is the desired microstructure, the other types get in the way of its growth. Martensite forms from the rapid cooling of austenite grains and its transformation process is still not well understood. With increasing grain size, there are more austenite grains and fewer grain boundaries. Therefore, there are fewer opportunities for microstructures like pearlite and bainite to form and more opportunities for martensite to form.

colorful glass representing austenite
Figure 5: The colorful glass pieces represent grains of austenite which transforms into the desirable martensite upon quenching. The black portions in between the color portions represent grain boundaries. Sites where pearlite or bainite will form upon quenching.

3. The method of quenching

As previously stated, the type of quench affects the cooling rate. Using oil, water, aqueous polymer quenchants, or air will yield a different hardness through the interior of the workpiece. This also shifts the hardenability curves. Water produces the most severe quench followed by oil and then air. Aqueous polymer quenchants provide quenching rates between those of water and oil and can be tailored to specific applications by changing the polymer concentration and temperature. The degree of agitation also affects the rate of heat removal. The faster the quenching medium moves across the specimen, the greater the quenching effectiveness. Oil quenches are generally used when a water quench may be too severe for a type of steel as it may crack or warp upon treatment.

metalworker quenching casts in an oil bath
Figure 6: Metalworker quenching casts in an oil bath

Machining Hardened Steels:

The type of cutter that should be chosen for processing tools chosen for machining a workpiece after hardening depends on a few different variables. Not counting the geometric requirements specific to the application, two of the most important variables are the material hardness and its hardenability. Some relatively high-stress applications require a minimum of 80% martensite to be produced throughout the interior of the workpiece. Usually, moderately stressed parts only require about 50% martensite throughout the workpiece. When machining a quenched metal with very low hardenability a standard coated solid carbide tool may work without a problem. This is because the hardest portion of the workpiece is limited to its surface. When machining a steel with a high hardenability it is recommended that you use a cutter with specialized geometry that is for that specific application. High hardenability will result in a workpiece that is hard throughout its entire volume. Harvey Tool has a number of different cutters for hardened steel throughout the catalog, including drills, end mills, keyseat cutters, and engravers.

Summary:

Hardenability is a measure of the depth to which a ferrous alloy may be hardened by the formation of martensite throughout its entire volume, surface to core. It is an important material property you must consider when choosing a steel as well as cutting tools for a particular application. The hardening of any steel depends on the size and shape of the part, the molecular composition of the steel, and the type of quenching method used.