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.

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

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.

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. If you need even smaller tooling, there are 4 flute options available down to .005” in diameter.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

5 Things to Know About Helical’s High Feed End Mills

Helical Solutions‘ High Feed End Mills provide many opportunities for machinists, and feature a special end profile to increase machining efficiencies. A High Feed End Mill is a High Efficiency Milling (HEM) style tool with specialized end geometry that utilizes chip thinning, allowing for drastically increased feed rates in certain applications. While standard end mills have square, corner radius, or ball profiles, this Helical tool has a specialized, very specific design that takes advantage of chip thinning, resulting in a tool that can be pushed harder than a traditional end mill.

Below are 5 things that all machinists should know about this exciting Helical Solutions product offering.

1. They excel in applications with light axial depths of cut

A High Feed End Mill is designed to take a large radial depth of cut (65% to 100% of the cutter diameter) with a small axial depth of cut (2.5% to 5% diameter) depending on the application. This makes High Feed End Mills perfect for face milling, roughing, slotting, deep pocketing, and 3D milling. Where HEM toolpaths involve light radial depths of cut and heavy axial depths of cut, High Feed End Mills utilize high radial depths of cut and smaller axial depths of cut.

2. This tool reduces radial cutting forces

The end profile of a High Feed End Mill is designed to direct cutting forces upward along the axis of the tool and into the spindle. This reduces radial cutting forces which cause deflection, allowing for longer reach tools while reducing chatter and other issues that may otherwise lead to tool failure. The reduction of radial cutting forces makes this tool excellent for use in machines with lower horsepower, and in thin wall machining applications.

3. High Feed End Mills are rigid tools

The design and short length of cut of High Feed End Mills work in tandem with the end geometry to produce a tool with a strong core, further limiting deflection and allowing for tools with greater reach lengths.

4. They can reduce cycle times

In high RDOC, low ADOC applications, High Feed End Mills can be pushed significantly faster than traditional end mills, saving time and money over the life of the tool.

5. High Feed End Mills are well suited for hard materials

The rigidity and strength of High Feed End Mills make them excellent in challenging to machine materials. Helical’s High Feed End Mills come coated with Tplus coating, which offers high hardness and extended tool life in high temp alloys and ferrous materials up to 45Rc.

In summary, High Feed End Mill tools with specialized end geometry that utilizes chip thinning and light axial depths of cut to allow for significantly increased feed rates in face milling, slotting, roughing, deep pocket milling, and 3D milling applications. The end profile of a High Feed End Mill applies cutting forces back up into the spindle, reducing radial forces that lead to deflection in long reach applications. Combining this end geometry with a stubby length of cut results in a tool that is incredibly rigid and well suited for harder, difficult to machine materials.

Benefits & Drawbacks of High and Low Helix Angles

While many factors impact the outcome of a machining operation, one often overlooked factor is the cutting tool’s helix angle. The Helix angle of a tool is measured by the angle formed between the centerline of the tool and a straight line tangent along the cutting edge.

A higher helix angle, usually 40° or more, will wrap around the tool “faster,” while a “slower” helix angle is usually less than 40°.

When choosing a tool for a machining operation, machinists often consider the material, the tooling dimensions and the flute count. The helix angle must also be considered to contribute to efficient chip evacuation, better part finish, prolonged tool life, and reduced cycle times.

Helix Angles Rule of Thumb

One general rule of thumb is that as the helix angle increases, the length of engagement along the cutting edge will decrease. That said,
there are many benefits and drawbacks to slow and high helix angles that can impact any machining operation.

Slow Helix Tool <40°

Benefits

  • Enhanced Strength – A larger core creates a strong tool that can resist deflection, or the force that will bend a tool under pressure.
  • Reduced Lifting – A slow helix will decrease a part from lifting off of the worktable in settings that are less secure.
  • Larger Chip Evacuation – The slow helix allows the tool to create a large chip, great for hogging out material.

Drawbacks

  • Rough Finish – A slow helix end mill takes a large chip, but can sometimes struggle to evacuate the chip. This inefficiency can result in a sub-par part finish.
  • Slower Feed Rate – The increased radial force of a slow helix end mill requires running the end mill at a slower feed rate.

High Helix Tool >40°

Benefits

  • Lower Radial Force – The tool will run quieter and smoother due to better shearing action, and allow for less deflection and more stability in thin wall applications.
  • Efficient Chip Evacuation – As the helix angle increases, the length of cutting edge engagement will decrease, and the axial force will increase. This lifts chips out and away, resulting in efficient chip evacuation.
  • Improved Part Finish – With lower radial forces, high helix tools are able to cut through material much more easily with a better shearing action, leaving an improved surface finish.

Drawbacks

  • Weaker Cutting Teeth – With a higher helix, the teeth of a tool will be thinner, and therefore thinner.
  • Deflection Risk – The smaller teeth of the high helix tool will increase the risk of deflection, or the force that will bend a tool under pressure. This limits how fast you can push high helix tools.
  • Increased Risk of Tool Failure – If deflection isn’t properly managed, this can result in a poor finish quality and tool failure.

Helix Angle: An Important Decision

In summary, a machinist must consider many factors when choosing tools for each application. Among the material, the finish requirements, and acceptable run times, a machinist must also consider the helix angle of each tool being used. A slow helix end mill will allow for larger chip formation, increased tool strength and reduce lifting forces. However, it may not leave an excellent finish. A high helix end mill will allow for efficient chip evacuation and excellent part finish, but may be subject to increased deflection, which can lead to tool breakage if not properly managed.

Selecting the Right Chamfer Cutter Tip Geometry

A chamfer cutter, or a chamfer mill, can be found at any machine shop, assembly floor, or hobbyist’s garage. These cutters are simple tools that are used for chamfering or beveling any part in a wide variety of materials. There are many reasons to chamfer a part, ranging from fluid flow and safety, to part aesthetics.

Due to the diversity of needs, tooling manufacturers offer many different angles and sizes of chamfer cutters, and as well as different types of chamfer cutter tip geometries. Harvey Tool, for instance, offers 21 different angles per side, ranging from 15° to 80°, flute counts of 2 to 6, and shank diameters starting at 1/8” up to 1 inch.

After finding a tool with the exact angle they’re looking for, a customer may have to choose a certain chamfer cutter tip that would best suit their operation. Common types of chamfer cutter tips include pointed, flat end, and end cutting. The following three types of chamfer cutter tip styles, offered by Harvey Tool, each serve a unique purpose.

Three Types of Harvey Tool Chamfer Cutters

Type I: Pointed

This style of chamfer cutter is the only Harvey Tool option that comes to a sharp point. The pointed tip allows the cutter to perform in smaller grooves, slots, and holes, relative to the other two types. This style also allows for easier programming and touch-offs, since the point can be easily located. It’s due to its tip that this version of the cutter has the longest length of cut (with the tool coming to a finished point), compared to the flat end of the other types of chamfer cutters. With only a 2 flute option, this is the most straightforward version of a chamfer cutter offered by Harvey Tool.

Type II: Flat End, Non-End Cutting

Type II chamfer cutters are very similar to the type I style, but feature an end that’s ground down to a flat, non-cutting tip. This flat “tip” removes the pointed part of the chamfer, which is the weakest part of the tool. Due to this change in tool geometry, this tool is given an additional measurement for how much longer the tool would be if it came to a point. This measurement is known as “distance to theoretical sharp corner,” which helps with the programming of the tool. The advantage of the flat end of the cutter now allows for multiple flutes to exist on the tapered profile of the chamfer cutter. With more flutes, this chamfer has improved tool life and finish. The flat, non-end cutting tip flat does limit its use in narrow slots, but another advantage is a lower profile angle with better angular velocity at the tip.

Type III: Flat End, End Cutting

Type III chamfer cutters are an improved and more advanced version of the type II style. The type III boasts a flat end tip with 2 flutes meeting at the center, creating a center cutting-capable version of the type II cutter. The center cutting geometry of this cutter makes it possible to cut with its flat tip. This cutting allows the chamfer cutter to lightly cut into the top of a part to the bottom of it, rather than leave material behind when cutting a chamfer. There are many situations where blending of a tapered wall and floor is needed, and this is where these chamfer cutters shine. The tip diameter is also held to a tight tolerance, which significantly helps with programing it.

In conclusion, there could be many suitable cutters for a single job, and there are many questions you must ask prior to picking your ideal tool. Choosing the right angle comes down to making sure that the angle on the chamfer cutter matches the angle on the part. One needs to be cautious of how the angles are called out, as well. Is the angle an “included angle” or “angle per side?” Is the angle called off of the vertical or horizontal? Next, the larger the shank diameter, the stronger the chamfer and the longer the length of cut, but now, interference with walls or fixtures need to be considered. Flute count comes down to material and finish. Softer materials tend to want less flutes for better chip evacuation, while more flutes will help with finish. After addressing each of these considerations, the correct style of chamfer for your job should be abundantly clear.

How to Select a Spindle

When trying to develop efficient processes, many machinists and programmers turn to tool selection first. It is true that tooling can often make a big difference in machining time, and speeds and feeds, but did you know that your machine’s spindle can have an equally impactful effect? The legs of any CNC machine, spindles are comprised of a motor, a taper for holding tools, and a shaft that will hold all of the components together. Often powered by electricity, spindles rotate on an axis which receives its input from the machine’s CNC controller.

Why is Choosing the Right Spindle Important?

Choosing the right spindle to machine your workpiece with is of very high importance to a successful production run. As tooling options continue to grow, it is important to know what tooling your spindle can utilize. Large diameter tools such as large end mills or face mills typically require slower spindle speeds and take deeper cuts to remove vast amounts of material. These applications require supreme machine rigidity and require a spindle with high torque.

Contrastingly, smaller diameter tools will need a higher-speed spindle. Faster speeds and feeds deliver better surface finishes and are used in a variety of applications. A good rule of thumb is that an end mill that is a half inch or smaller will run well with lower torque.

Types of CNC Spindles

After finding out what you should look for in a spindle, it is time to learn about your different options. Spindles typically vary by the type, style of the taper, or its size. The taper is the conical portion of the tool holder that fits inside of the opening of the spindle. Every spindle is designed to mate with a certain taper style and size.

CAT and BT Holders

This is the most widely utilized holder for milling in the United States. Referred to as “V-flange holders,” both of these styles need a retention knob or pull stud to be secured within the machine spindle. The BT (metric style) is popular overseas.

HSK Holders

This type of holder is a German standard known as “hollow shank taper.” The tapered portion of the holder is much shorter than its counterparts. It also engages the spindle in a different way and does not require a pull stud or retention knob. The HSK holder is utilized to create repeatability and longer tool life – particularly in High Efficiency Milling (HEM) applications.

All of these holders have benefits and limitations including price, accuracy, and availability. The proper selection will depend largely on your application requirements.

Torque vs. Horsepower

Torque is defined as force perpendicular to the axis of rotation across a distance. It is important to have high torque capabilities when using an end mill larger than ½ inch, or when machining a difficult material such as Inconel. Torque will help put power behind the cutting action of the tool.

Horsepower refers to the amount of work being done. Horsepower is important for smaller diameter end mills and easy-to-machine materials like aluminum.

You can think of torque as a tractor: It can’t go very fast, but there is a lot of power behind it. Think of horsepower as a racecar: It can go very fast but cannot pull or push.

Torque-Horsepower Chart

Every machine and spindle should come with a torque horsepower chart. These charts will help you understand how to maximize your spindle for torque or horsepower, depending on what you need:

Image Source: HAAS Machine Manual

Proper Spindle Size

The size of the spindle and shank taper corresponds to the weight and length of the tools being used, as well as the material you are planning to machine. CAT40 is the most commonly used spindle in the United States. These spindles are great for utilizing tools that have a ½ inch diameter end mill or smaller in any material. If you are considering using a 1 inch end mill in a material like Inconel or Titanium, a CAT50 would be a more appropriate choice. The higher the taper angle is, the more torque the spindle is capable of.

While choosing the correct tool for your application is important, choosing a tool your spindle can utilize is paramount to machining success. Knowing the amount of torque required will help machinists save a lot of headaches.

How Boring Bar Geometries Impact Cutting Operations

Boring is a turning operation that allows a machinist to make a pre-existing hole bigger through multiple iterations of internal boring. It has a number of advantages over traditional drilling methods:

  • The ability to cost-effectively produce a hole outside standard drill sizes
  • The creation of more precise holes, and therefore tighter tolerances
  • A greater finish quality
  • The opportunity to create multiple dimensions within the bore itself

 

Solid carbide boring bars, such as those offered by Micro 100,  have a few standard dimensions that give the tool basic functionality in removing material from an internal bore. These include:

Minimum Bore Diameter (D1): The minimum diameter of a hole for the cutting end of the tool to completely fit inside without making contact at opposing sides

Maximum Bore Depth (L2): Maximum depth that the tool can reach inside a hole without contact from the shank portion

Shank Diameter (D2): Diameter of the portion of the tool in contact with the tool holder

Overall Length (L1): Total length of the tool

Centerline Offset (F): The distance between a tool’s tip and the shank’s centerline axis

Tool Selection

In order to minimize tool deflection and therefore risk of tool failure, it is important to choose a tool with a max bore depth that is only slightly larger than the length it is intended to cut. It is also beneficial to maximize the boring bar and shank diameter as this will increase the rigidity of the tool. This must be balanced with leaving enough room for chips to evacuate. This balance ultimately comes down to the material being bored. A harder material with a lower feed rate and depths of cut may not need as much space for chips to evacuate, but may require a larger and more rigid tool. Conversely, a softer material with more aggressive running parameters will need more room for chip evacuation, but may not require as rigid of a tool.

Geometries

In addition, they have a number of different geometric features in order to adequately handle the three types of forces acting upon the tool during this machining process. During a standard boring operation, the greatest of these forces is tangential, followed by feed (sometimes called axial), and finally radial. Tangential force acts perpendicular to the rake surface and pushes the tool away from the centerline. Feed force does not cause deflection, but pushes back on the tool and acts parallel to the centerline. Radial force pushes the tool towards the center of the bore.

 

Defining the Geometric Features of Boring Bars:

Nose Radius: the roundness of a tool’s cutting point

Side Clearance (Radial Clearance): The angle measuring the tilt of the nose relative to the axis parallel to the centerline of the tool

End Clearance (Axial Clearance): The angle measuring the tilt of the end face relative to the axis running perpendicular to the centerline of the tool

Side Rake Angle: The angle measuring the sideways tilt of the side face of the tool

Back Rake Angle: The angle measuring the degree to which the back face is tilted in relation to the centerline of the workpiece

Side Relief Angle: The angle measuring how far the bottom face is tilted away from the workpiece

End Relief Angle: The angle measuring the tilt of the end face relative to the line running perpendicular to the center axis of the tool

Effects of Geometric Features on Cutting Operations:

Nose Radius: A large nose radius makes more contact with the workpiece, extending the life of the tool and the cutting edge as well as leaving a better finish. However, too large of a radius will lead to chatter as the tool is more exposed to tangential and radial cutting forces.

Another way this feature affects the cutting action is in determining how much of the cutting edge is struck by tangential force. The magnitude of this effect is largely dependent on the feed and depth of cut. Different combinations of depth of cuts and nose angles will result in either shorter or longer lengths of the cutting edge being exposed to the tangential force. The overall effect being the degree of edge wear. If only a small portion of the cutting edge is exposed to a large force it would be worn down faster than if a longer portion of the edge is succumb to the same force. This phenomenon also occurs with the increase and decrease of the end cutting edge angle.

End Cutting Edge Angle: The main purpose of the end cutting angle is for clearance when cutting in the positive Z direction (moving into the hole). This clearance allows the nose radius to be the main point of contact between the tool and the workpiece. Increasing the end cutting edge angle in the positive direction decreases the strength of the tip, but also decreases feed force. This is another situation where balance of tip strength and cutting force reduction must be found. It is also important to note that the angle may need to be changed depending on the type of boring one is performing.

Side Rake Angle: The nose angle is one geometric dimension that determines how much of the cutting edge is hit by tangential force but the side rake angle determines how much that force is redistributed into radial force. A positive rake angle means a lower tangential cutting force as allows for a greater amount of shearing action. However, this angle cannot be too great as it compromises cutting edge integrity by leaving less material for the nose angle and side relief angle.

Back Rake Angle: Sometimes called the top rake angle, the back rake angle for solid carbide boring bars is ground to help control the flow of chips cut on the end portion of the tool. This feature cannot have too sharp of a positive angle as it decreases the tools strength.

Side and End Relief Angles: Like the end cutting edge angle, the main purpose of the side and end relief angles are to provide clearance so that the tools non-cutting portion doesn’t rub against the workpiece. If the angles are too small then there is a risk of abrasion between the tool and the workpiece. This friction leads to increased tool wear, vibration and poor surface finish. The angle measurements will generally be between 0° and 20°.

Boring Bar Geometries Summarized

Boring bars have a few overall dimensions that allow for the boring of a hole without running the tool holder into the workpiece, or breaking the tool instantly upon contact. Solid carbide boring bars have a variety of angles that are combined differently to distribute the 3 types of cutting forces in order to take full advantage of the tool. Maximizing tool performance requires the combination of choosing the right tool along with the appropriate feed rate, depth of cut and RPM. These factors are dependent on the size of the hole, amount of material that needs to be removed, and mechanical properties of the workpiece.

 

Green Manufacturing: Lasting Environment & Shop Benefits

“Green Manufacturing” has become a common phrase used by many in America’s largest industry. It is defined by Goodwin College as “the renewal of production processes and the establishment of environmentally friendly operations within the manufacturing field.” Taking the time to rethink dated processes can save you time, money, and help build your reputation as a state-of-the-art business. The establishment of environmentally friendly machining processes is a huge leap in the right direction of creating an eco-friendly business.

Green Manufacturing is the next logical step forward for the industry.

How to Get Started with Green Manufacturing

The first step you should take on your march toward a more sustainable machine shop, and green manufacturing, is an evaluation of your facilities environmental impact. The most common method for environmental impact assessment of the manufacturing process is Life Cycle Assessment or LCA. ISO 14040 defines LCA as the compilation and evaluation of the inputs, outputs, and the potential environmental impacts of a product system throughout its life cycle.

4 Questions to Ask Yourself:

  1. Goal Definition and Scoping – What am I trying to achieve in this investigation?
  2. Inventory Analysis – What are the quantified inputs (energy, water, materials, etc.) and outputs (air emission, wastewater)?
  3. Impact Assessment – How do these things affect the environment?
  4. Interpretation – What can I change to make my processes more efficient and eco-friendly?

There are databases available to help with the inventory analysis. These databases collect information such as feed rate, cutting speed, tool diameter, cutting time, coolant properties, and then calculate all the material, and energy inputs and outputs.

Understanding the Impact of Cutting Fluids

Cutting fluids are most likely the number one pollutant in your machine shop, and are getting in your way of achieving green manufacturing. According to Modern Manufacturing Processes, North American manufacturers consumed more than 2 billion gallons in 2002, and the metal working fluid market has only grown since then. Cutting fluids have a number of benefits to the machining process, mostly involving cooling of the cutting region, lubrication, and chip evacuation.

Contaminants

Getting the most out of your coolant is a key factor of cost efficiency in any machine shop. Therefore, one of the largest problems you are likely to face, or are currently facing, is the deterioration of cutting fluid performance due to contaminants. The most common types of contaminants include:

  1. Free oils (tramp or sump oil) – Liquid that lubricates the gears and equipment of CNC machine seeping into the cutting fluid
  2. Coarse Particulates – Relatively larger solid waste, chips, and swarf
  3. Fine Particulates – Extremely small pieces of the workpiece or cutting tool that usually consist of heavy metals such as cobalt, cadmium, chromium, aluminum, and lead
  4. Microorganisms – Bacteria and fungi that grow inside the walls and pipes of the CNC machine

Coarse particulates such as chips and swarf are generally easily extracted using an H-Chain, chain and flight, push bar, or a flume system. Fine particulates are more difficult as they require either separation or filtration in the form of setting tanks, foam separators, centrifugal separation, or magnetic separators. Free oil can also be removed through filtration but can also be taken care of quickly and easily with a skimmer.

The right filtration system can both save machine shops money and help the environment.

Microorganisms are the most difficult to remove as they can be a tenth of the size of fine particulates. “Monday morning stink” is a common side effect of anaerobic bacteria excreting hydrogen sulfide during their metabolic processes. These organisms are one of the main reasons coolant has to be drained and changed from a machine every few months. Advancements in technology over the past few decades have made it possible for membrane microfiltration systems to separate biomass, as well as oil from coolant fluids. With these types of systems, operators will no longer have to use problematic biocides as these have troublesome health effects for both the environment and employees. However, it is important to note that most of the microorganisms aren’t growing in the cutting fluid but on the walls/pipes of the machine or buried in the residue of chips at the bottom of the tank.

Some ways of reducing microorganism build-up in your shop include:

  • Keeping machines clean – sludge, swarf, and chips can be a breeding ground for bacteria
  • Reduce organic contamination – spit, sweat, tobacco juice, and organic matter are all a food source for microorganisms
  • Reduce the amount of tramp oil – This can also be a food source

A dirty pile of chips where bacteria will grow and stink up your machine.

Types of Cutting Fluids

A good cutting fluid should have a high flash point, good adhesiveness, high thermal stability, and high oxidative stability. A high flash point is necessary as the fluid should not catch fire at high temperatures (gasoline has a low flash point). Good adhesiveness allows fluid to stick to the surface of the workpiece. This creates a layer between the cutting tool and the workpiece, helping to separate them and thus, reducing friction. Greater amounts of friction leads to higher cutting force, which leads to higher cutting temperatures.

High cutting temperatures are problematic, as this causes the cutting tool to wear faster and can also cause your workpiece to workharden. High thermal stability means that at high temperatures, the fluid should have a low viscosity (an example of a fluid with high viscosity would be honey at room temperature). A lower viscosity in the cutting region allows for a lower amount of friction, and therefore lower amounts of heat and cutting force. A cutting fluids oxidative stability ultimately decides how long that cutting fluid can be used. After a while, oil begin to oxidize, which then causes its viscosity and amount of deposits of sludge to rise.

Excessive amounts of coolants can mean an excessive amount of waste.

For the purpose of this article, cutting fluids will be placed into two broad categories: biodegradable and non-biodegradable.

Non-Biodegradable Coolants

Non-biodegradable coolants are petroleum-based. They have high human and ecological toxicity, which results in occupational health risks. They also have a complicated disposal processes.

Biodegradable Coolants

Biodegradable coolants are plant-based. These are usually manufactured from vegetables such as soy, coconut and canola, or non-edible plants such as neem, karanja, and jatropha. This factor makes them a renewable resource and less toxic to humans, as well as the environment.

In recent years, some modified vegetable-based oils have surpassed petroleum based oils in performance in regards to surface finish, heat suppression and lubrication. One study, published in Science Direct, centered on turning in 304 stainless steel revealed that coconut oil with a boric acid additive was significantly better at combating tool flank wear and surface roughness when compared to two other cutting fluids. This was due to the vegetable-based solutions high thermal stability.

Another study, published in IOP Science, found that a combination of neem and karanja oil was superior to SAE 20W40 (petroleum based oil) in regards to lubrication when drilling mild steel. The results showed that the vegetable-based oil solution reduced the cutting force of the operation due to its higher viscosity and adhesiveness. This ultimately led to a better surface finish on the part.

Summary of Cost Efficient Coolant Changes You Can Make

  • Reduce microorganism build up in your machines by keeping the machines clean and reducing amount of outside contamination
  • Install a membrane microfiltration system
  • Switch to a more efficient and biodegradable cutting fluid

The Positive Green Machining Impact of Dry Machining

Dry machining should be utilized whenever the opportunity presents itself, as the costs and environmental issues associated with cutting fluid obtainment, management, and disposal are eliminated. Another benefit to dry machining is the absence of thermal shock. When the cutter exits the cut but coolant is still blasting, the large temperature fluctuation (thermal shock) will cause the cutting edge to break down quicker than if it were to run hot full time. Dry machining is most prevalent in machining operations with interrupted cuts or when cutting hardened steels. It is especially popular in milling operations with high speeds and feeds. Cutting with high running parameters allows for most of the heat to be dispersed into the chips rather than into the workpiece. This is also the case when machining hardened steels.

Ideal Tooling for Dry Machining

The ideal cutting tool should be more heat resistant, and less heat generative. Carbide is a good substrate as it is extremely hard and strong. Coated tools are the best option for dry machining as they have improved thermal insulation as well as improved self-lubrication.

The Positive Affect of Minimum Quantity Lubrication (MQL)

  • Significantly reduced fluid consumption
  • Safer cutting fluids and lubricants
  • Reduced health hazards for employees
  • Cleaner shop environment
  • Reduced maintenance

Because such a small quantity of fluid is used in MQL, this make it a perfect application to use slightly pricier vegetable-based oils. MQL has been found to be most effective in sawing and drilling operations.

The Benefits of Green Manufacturing

Taking a second look at your current machining operations through and environmentalist lens can save you time, money, and create a less hazardous work place for your employees. Using the techniques above, one can approximate shop efficiency and make appropriate changes for the benefit of current and future generations.

The Geometries and Purposes of a Slitting Saw

When a machinist needs to cut material significantly deeper than wide, a Slitting Saw is an ideal choice to get the job done. A Slitting Saw is unique due to its composition and rigidity, which allows it to hold up in a variety of both straightforward and tricky to machine materials.

What is a Slitting Saw?

A Slitting Saw is a flat (with or without a dish), circular-shaped saw that has a hole in the middle and teeth on the outer diameter. Used in conjunction with an arbor, a Slitting Saw is intended for machining purposes that require a large amount of material to be removed within a small diameter, such as slotting or cutoff applications.

Other names for Slitting Saws include (but are not limited to) Slitting Cutters, Slotting Cutters, Jewelers Saws, and Slitting Knives. Both Jewelers Saws and Slitting Knives are particular types of Slitting Saws. Jewelers Saws have a high tooth count enabling them to cut tiny, precise features, and Slitting Knives are Slitting Saws with no teeth at all. On Jewelers Saws, the tooth counts are generally much higher than other types of saws in order to make the cuts as accurate as possible.

Key Terminology

Why Use a Slitting Saw?

These saws are designed for cutting into both ferrous and non-ferrous materials, and by utilizing their unique shape and geometries, they can cut thin slot type features on parts more efficiently than any other machining tool.

Common Applications:

  1. Separating Two Pieces of Material
    1. If an application calls for cutting a piece of material, such as a rod, in half, then a slitting saw will work well to cut the pieces apart while increasing efficiency.
  2. Undercutting Applications
    1. Saws can perform undercutting applications if mounted correctly, which can eliminate the need to remount the workpiece completely.
  3. Slotting into Material
    1. Capable of creating thin slots with a significant depth of cut, Slitting Saws can be just the right tool for the job!

When Not to Use a Slitting Saw

While it may look similar to a stainless steel circular saw blade from a hardware store, a Slitting Saw should never be used with construction tools such as a table or circular saw.  Brittle saw blades such as slitting saws will shatter when used on manual machines, and can cause injury when not used on the proper set up.

In Conclusion

Slitting Saws can be beneficial to a wide variety of machining processes, and it is vital to understand their geometries and purpose before attempting to utilize them in the shop. They are a great tool to have in the shop and can assist with getting jobs done as quickly and efficiently as possible.