Traditional vs. Free Cutting Finishing Core Tools: Which Is Right for Your Application?

Precision cutting plays a pivotal role in the manufacturing of honeycomb core. CoreHog, a leading provider of composite cutting solutions, offers two distinct styles of Finishing Core Tools: Traditional Finishing Core Tools and Free Cutting Tools. In this post, we explore the advantages and limitations of both Traditional Finishing Core Tools and Free Cutting Core Tools, helping you determine the right choice for your unique manufacturing needs.

CoreHog’s Large Core Finishing Tool

Advantages of Traditional Finishing Core Tools:

CoreHog’s Finishing Core Tools are designed to handle substantial cutting tasks, efficiently. With three size ranges available, they excel at removing high volumes of material and boast excellent tool life, making them ideal for production applications.

Assembly Configuration of CoreHog’s Large & Free Cutting Finishing Core Tools


However, these tools may pose limitations in specific applications. Traditional tools exert tool pressure, but depending on the tool geometry and part profile, the pressure may be too much for the part. This becomes more pronounced when cutting knife edge features such as chamfers and bevels, where the pressure exerted by the tool can cause the part to arch, dislodging it from the table, and ultimately causing it to deviate from specifications.

Introducing Free Cutting Core Finishing Tools:­­

To address the limitations of traditional honeycomb core finishing tools when cutting knife edge features, CoreHog offers Free Cutting Finishing Core Tools. The innovative design reduces tool pressure seen in both the Coreslicer and CoreHogger. The Free Cutting Coreslicer features a more acute and sharper angle, reducing the upward pressure exerted on the part during cutting.

 Differentiation of angle between the Large Coreslicer and the Free Cutting Coreslicer

Further, these tools feature a CoreHogger with a reduced diameter, allowing for greater offset between the CoreHogger and Coreslicer. This allows the Coreslicer to be more forward and free cutting, engaging with the material prior to the CoreHogger and reducing the resulting pressure typically exhibited by the CoreHogger.  

Reduced diameter design of Free Cutting CoreHogger decreases tool pressure on the part.

When to Use Free Cutting Tools:

CoreHog’s Free Cutting Core Finishing Tools are particularly well-suited for applications involving chamfering, beveling, and cutting angled profiles in honeycomb core materials. By reducing pressure and preventing lifting on the part, these tools ensure precise cuts without compromising part quality.

­­Traditional vs. Free Cutting Core Finishing Tool: Summarized

In conclusion, choosing the right cutting tool is crucial for achieving precise results in composite manufacturing. While traditional finishing core tools excel in handling substantial tasks, they may pose challenges when cutting angled profiles in honeycomb core materials. CoreHog’s Free Cutting Core Finishing Tools offer a solution by minimizing pressure on the part, making them ideal for chamfering, beveling, and most other angled profiles. However, in finicky applications where the knife edge part is extremely shallow, a Valve Stem Cutter may still be necessary to achieve your desired cut. By understanding your specific cutting requirements, you can select the most suitable tool for your application, ensuring optimal results in your honeycomb manufacturing processes.

Multi-Axis Finisher Q&A

What is a Multi-Axis Finisher?

A tool that uses an extremely large radius to increase finishing performance in two different ways, depending on the needs of the machinist. Either the Multi-Axis Finisher will provide a better surface finish than a traditional Ball End Mill in the same amount of time, or will provide the same surface finish in far less time than a traditional Ball End Mill. A middle ground with improved surface finish and reduced cycle time is also easily achievable.

What Are Other Names for Multi-Axis Finishers?

Multi-Axis Finishers are oftentimes referred to as Barrel Cutters or Conical Barrel Mills or Circle Segment Cutters, among many others.

What Are the Different Forms of Multi-Axis Finishers, and How Do They Differ?

There are several different forms of Multi-Axis Finishers, including Lens, Taper, Oval, and Barrel. With a Lens Form, there’s a large radius on the end of the tool that’s in line with the tool axis. Taper Form, in contrast, has three tangential radii and a large radius defined at a specific angle relative to the tool axis. An Oval Form has two tangential radii, offering additional angle flexibility, while a Barrel Form has a large radius on the OD of the tool.

The most significant benefit is oftentimes observed utilizing a Taper Form Multi-Axis Finisher, as the radius of this tool can become vastly large on this form, while the others are more limited. However, this great benefit also comes with the least amount of flexibility in terms of approach to a workpiece.

What Are the Benefits of a Multi-Axis Finisher?

There are two clear benefits to using a Multi-Axis Finisher, compared to a Ball End Mill: Increased surface finish, and reduced cycle time (Or most likely both, concurrently).

What is a Benefit Multiple?

Helical Solutions is the industry’s premier manufacturer of Multi-Axis Finishers, and the Benefit Multiple is a significant reason why. Helical specifies the theoretical benefit that can be seen with its Multi-Axis Finishers, providing machinists direct insight into the gains that can be realized with these tools.

Benefit Multiple refers to the Cusp Height, correlated directly with the theoretically-achievable surface finish. Assuming the same cusp height from a Ball End Mill to a Multi-Axis Finisher, the Benefit Multiple relates to the time savings that could be seen in a machinists’ toolpath. For example, a Benefit Multiple of 4 would result in a toolpath ¼ as long as for a Ball End Mill of the same diameter. The stepover pass-to-pass would be 400% as much as a Ball End Mill to keep the same cusp.

When Should I Not Use a Multi-Axis Finisher?

Multi-Axis Finishers are best applied to wide-open surface areas; or large, smooth contours rather than small features or tight areas. Application of these tools will always be on a case-by-case basis. For help with your specific application, contact Helical Solutions Technical Support at 866-543-5422.

How Can I Get the Most Out of My Multi-Axis Finisher?

Multi-Axis finishers are best utilized when working further towards the OD of the tool. Tapered Form Multi-Axis Finishers are the most obvious choice for this, as its nose radius is small and has the least amount of efficiency. Similarly to a ball end mill, working near the center will have limited cutting ability, while the OD of the tool will see the full surface footage of the programmed RPM.

Taper Form Multi-Axis Finishers should be used when tilted at the specified taper angle. Oval Form Multi-Axis Finishers should be used towards the OD. Lens Form Multi-Axis Finishers should be tilted to avoid working on-center.

Lens Form Multi-Axis Finishers Look Like a High Feed End Mill. Can I Use it That Way?


Yes. However, there are differences in the form, and while a Lens Form Multi-Axis Finisher could theoretically be used as a High Feed End Mill, the two tools are not interchangeable.  A High Feed End Mill would not be the best choice for Multi-Axis Finishing, nor would a Lens Form Multi-Axis Finisher be our first recommendation for feed milling.

Do I need special software to program Multi-Axis Finishers?

Yes. A number of years ago, there were only a few CAM software packages that supported the programming of these specific forms. Nowadays, most CAM software providers have some degree of support for this method. Two of the first CAM software offerings to support this were MasterCAM and Hypermill, though many additional options exist today.

Why haven’t I heard of Multi-Axis Finishers Until Now?

In the grand scheme of things, Multi-Axis Finishers provide a very new approach to finishing, having been developed within the last handful of years.  Similar to High Efficiency Milling, these tools offer a new technique to approach your workpiece, offering increased efficiency and reduced cycle times.  Compared to the history of milling, modern tool manufacturing and CAM software have only just become able to program these unique forms.  Multi-axis finishers are positioned to revolutionize the world of finishing.

For more information on Multi-Axis Finishers, visit Multi-Axis Finishers: The Key to Amazing Surface Finish.

Spot Drilling: The First Step to Precision Drilling

Drilling an ultra-precise hole can be tough. Material behavior, surface irregularities, and drill point geometry can all be factors leading to inaccurate holes. A Spot Drill, if used properly, will eliminate the chance of drill walking and will help to ensure a more accurate final product.

Choosing a Spot Drill

Ideally, the center of a carbide drill should always be the first point to contact your part. Therefore, a spotting drill should have a slightly larger point angle than that of your drill. Common drill point angles range from 118° to 140° and larger. Shallower drill angles are better suited to harder materials like steels due to increased engagement on the cutting edges. Aluminums can also benefit from these shallower angles through increased drill life. While these drills wear less and more evenly, they are more prone to walking, therefore creating a need for a proper high performance spot drill in a shallow angle to best match the chosen drill.

Five Valor holemaking high performance spot drills displayed on top of a workpiece with a purple product packaging container in front

If a spotting drill with a smaller point angle than your drill is used, your drill may be damaged due to shock loading when the outer portion of its cutting surface contacts the workpiece before the center. Using a drill angle equal to the drill angle is also an acceptable situation. Figure 1 illustrates the desired effect. On the left, a drill is entering a previously drilled spot with a slightly larger angle than its point. On the right, a drill is approaching an area with an angle that is far too small for its point.

Proper Spot Angle Diagram

Marking Your Spot

A Spotting Drill’s purpose is to create a small divot to correctly locate the center of a drill when initiating a plunge. However, some machinists choose to use these tools for a different reason – using it to chamfer the top of drilled holes. By leaving a chamfer, screw heads sit flush with the part once inserted.

Spot Drill

What Happens if I Use a Spot Drill with an Improper Angle?

Using a larger angle drill will allow the drill to find the correct location by guiding the tip of the drill to the center. If the outer diameter of a carbide drill were to contact the workpiece first, the tool could chip. This would damage the workpiece and result in a defective tool. If the two flutes of the drill were slightly different from one another, one could come into contact before the other. This could lead to an inaccurate hole, and even counteract the purpose of spot drilling in the first place.

Avoiding CNC Drill Walking With a Spotting Drill

Few CNC machining applications demand precision like drilling. The diameter hole size, hole depth, part location, and finish are all important and provide little recourse if not up to specifications. That said, accuracy is paramount – and nothing leads to inaccurate final parts faster than drill walking, or the inadvertent straying from a drill’s intended location during the machining process. So how does drill walking occur, and how can one prevent it?

To understand drill walking, think about the act of striking a nail with a hammer, into a piece of wood. Firm contact to a sharp nail into an appropriate wood surface can result in an accurate, straight impact. But if other variables come into play – an uneven surface, a dull nail, an improper impact – that nail could enter a material at an angle, at an inaccurate location, or not at all. With CNC Drilling, the drill is obviously a critical element to a successful operation – a sharp, unworn cutting tool – when used properly, will go a long way toward an efficient and accurate final part.

To mitigate any variables working against you, such as an uneven part surface or a slightly used drill, a simple way to avoid “walking” is to utilize a Spotting Drill. This tool is engineered to leave a divot on the face of the part for a drill to engage during the holemaking process, keeping it properly aligned to avoid a drill from slipping off course.

When Won’t a Spot Drill Work for My Application?

When drilling into an extremely irregular surface, such as the side of a cylinder or an inclined plane, this tool may not be sufficient to keep holes in the correct position. For these applications, flat bottom versions or Flat Bottom Counterbores may be needed to creating accurate features.

Harvey tool spot drill zoomed in on the tip of the drill
Harvey Tool Spot Drill

Understanding Key Qualities in Micro 100’s Offering of Micro-Quik Quick Change Tool Holders

Did you know that, along with supplying the machining industry with premier turning tools, Micro 100 also fully stocks tool holders for its proprietary Micro-Quik Quick Change Tool Holder System? In fact, Micro 100’s Spring 2021 Product Catalog introduced new “headless” style tool holders, which are revolutionizing the machine setup process for turning operations.

This “In the Loupe” guide is designed to provide you with insight for navigating Micro 100’s offering, and to help you select the optimal holder style for your operation.

Micro 100 ad showing four different tool holders

Understanding Micro 100’s Micro-Quik

Micro 100’s Micro-Quik is unlike any other tool change system you may have seen from other tool manufacturers because of its incredible axial and radial repeatability and its ease of use. This foolproof system delivers impressive repeatability, tip-to-tip consistency, and part-to-part accuracy, all the while resulting in tool changes that are 90 % faster than conventional methods.

In all, a tool change that would regularly take more than 5 minutes is accomplished in fewer than 30 seconds.

Micro 100 Quick Change Tool Holder Selection

Straight Style, Headless Tool Holders

When using a straight style tool holder, you will enjoy significantly enhanced versatility during the machine set up process. These holders are engineered specifically for use in any Swiss, standard lathe, or multi-function lathe, and allow for adjustable holder depth in a tooling block. Radial coolant access ports provide easier access to coolant and the ability to utilize coolant through functionality in tooling blocks that share a static and live tool function, and cannot be plumbed through the back of the holder. Further, their headless design allows for installation through the backside of the tooling block in machines where the work envelope is limited, allowing for a simplified installation process.

Created by Harvey Performance Company Application Engineers, the following videos outline the simple process for inserting each style of Micro 100 Straight Tool Holder into a tooling block.

Micro 100 Straight Holder, Plumbed Style (QTS / QTSL)

In the video, you’ll notice that the first step is to place your Micro-Quik tool in this quick change holder, and align it with the locating pin. Then, tighten the locating and locking screw into the whistle notch. This forces the tool against the locking pin, and allows for repeatable accuracy, every time. From there, the quick change tool holder can be installed as a unit into a tooling block. When desired tool position is achieved, set screws can be tightened to lock the holder in place.

Micro 100 Straight Holder, Plumbed & Ported Style (QTSP / QTSPL)

This unique Micro 100 quick change tool holder style is plumbed and ported, allowing for enhanced versatility and coolant delivery efficiency. The setup process using this style of holder is also simple. First, place your Micro 100 quick change tool into the holder, and align it with the locating pin. From there, tighten the locating and locking screw into the whistle notch, forcing the tool against the locating pin and allowing for repeatable accuracy, every time. When plumbed coolant is being used, remove the plumbed plug in the back of the holder, and connect the appropriate coolant adapter and line. Then, the holder can be installed as a unit into the tooling block and locked into place with set screws.

When using ported coolant, make sure that the coolant plug in the back of the holder is tightly installed. Then, be sure to only use one of the radial ports. Simply plug the two that aren’t in use. Install the provided porting adapter to allow for coolant access. Porting options allow for coolant capabilities in machine areas where coolant is not easily accessible.

Headed Tool Holders

headed quick change tool holder

Micro 100’s original quick change tool holder for its Micro-Quik system, this style of tool holder for lathe applications features a unique “3 point” locking and locating system to ensure repeatability. When conducting a tool change with this tool holder style, you must follow a simple, 3-step process:

  1. Loosen the tool holder’s set screw
  2. Remove the used tool from the holder
  3. Insert the new tool and retighten the set screw

These headed holders are plumbed through the back of the holder for NPT coolant connection and are available in standard length and long length styles.

Try Micro 100’s “Headless” Tool Holders for Incredible Flexibility

Double-Ended Modular Tool Holder System

double ended quick change tool holder

For twin spindle and Y-axis tooling block locations, Micro 100 fully stocks a double-ended modular system. Similar to its single-ended counterparts, this modular is headless, meaning it enhances machine access during the tool block installation process, and the holder depth can be adjusted while in the block. Because this system is double-ended, however, there is obviously no plumbed coolant option through the end of the tool. Instead, coolant is delivered via an external coolant port, the adapter for which is included in the purchase of the modular system. Right hand and left hand tool holders are designed so the set screws are facing the operator for easy access. Both right and left hand styles are designed for right hand turning.

Enjoy Quick Change Tool Holding Confidence & Ease of Use

When opting for a quick change system, machinists long for simplicity, versatility, and consistency. Though many manufacturers have a system of their own, Micro 100’s Micro-Quik sets itself apart with axial and radial repeatability, and tip-to-tip consistency. Further, Micro 100 fully stocks several quick change tool holder options, allowing a machinist to select the style that best fits their application.

Micro100 also manufactures and stocks a wide variety of boring tools for the Micro-Quik. Click here to learn more.

For more information on selecting the appropriate quick change tool holder for your job, view our selection chart or call an experienced Micro 100 technical engineer at 800-421-8065.

quick change tool holder selection chart for Micro100

The 3 Critical Factors of Turning Speeds and Feeds

Many factors come into play when determining a proper turning speeds and feeds and depth of cut strategy for turning operations. While three of these factors – the ones we deemed to be among the most critical – are listed below, please note that there are many other considerations that are not listed, but that are also important. For instance, safety should always be the main focus of any machining operation, as improper cutting tool parameters can test a machine’s limits, resulting in an accident that can potentially cause significant bodily harm.

Machine condition, type, capabilities, and set-up are all significantly important to an overall successful turning operation, as is turning tool and holder selection.

Turning Speeds and Feeds Factor 1: Machine Condition

The condition of your machine should always be considered prior to beginning a machining operation on a lathe. Older machines that have been used for production operations where hard or abrasive materials are machined tend to have a large amount of backlash, or wear, on the machine’s mechanical parts. This can cause it to produce less than optimal result and may require that a tooling manufacturer’s recommended speeds and feeds parameters need to be dialed back a bit, as to not run the machine more aggressively than it can handle.

turning machine engaging with workpiece

Factor 2: Machine Type and Capabilities

Before dialing in turning speeds and feeds, one must understand their machine type and its capabilities. Machines are programmed differently, depending on the type of turning center being used: CNC Lathe or Manual Lathe.

CNC Lathe Turning Centers

With this type of machine, the part and tool have the ability to be set in motion.

CNC lathe turning centers can be programmed as a G96 (constant surface footage) or G97 (constant RPM). With this type of machine, the maximum allowable RPM can be programmed using a G50 with an S command. For example, inputting a G50 S3000 into your CNC program would limit the maximum RPM to 3,000. Further, with CNC Lathe Turning Centers, the feed rate is programmable and can be changed at different positions or locations within a part program.

Manual Lathe Turning Centers

With this type of machine, only the part is in motion, while the tool remains immobile.

For manual lathe turning centers, parameters are programmed a bit differently. Here, the spindle speed is set at a constant RPM, and normally remains unchanged throughout the machining operation. Obviously, this puts more onus on a machinist to get speed correct, as an operation can quickly be derailed if RPM parameters are not optimal for a job. Like with CNC lathe turning centers, though, understanding your machine’s horsepower and maximum feed rate is critical.

Factor 3: Machine Set-Up

image demonstrating proper tool setup beside depiction of excessive tool stickout
Excessive Tool Stickout. Digital Image, Hass Automation. https://www.haascnc.com/service/troubleshooting-and-how-to/troubleshooting/lathe-chatter—troubleshooting.html

Machining Conditions

When factoring in your machine set-up, machining conditions must be considered. Below are some ideal conditions to strive for, as well as some suboptimal machining conditions to avoid for dialing in proper turning speeds and feeds.

Ideal Machining Conditions for Turning Applications

  • The workpiece clamping or fixture is in optimal condition, and the workpiece overhang is minimized to improve rigidity.
  • Coolant delivery systems are in place to aid in the evacuation of chips from a part and help control heat generation.

Suboptimal Machining Conditions for Turning Applications

  • Utilizing turning tools that are extended for reach purposes, when not necessary, causing an increased amount of tool deflection and sacrificing the rigidity of the machining operations.
  • The workpiece clamping or fixturing is aged, ineffective, and in poor condition.
  • Coolant delivery systems are missing, or are ineffective
  • Machine does not feature any guarding or enclosures, resulting in safety concerns.

Cutting Tool & Tool Holder Selection

As is always the case, cutting tool and tool holder selection are pivotal. Not all turning tool manufacturers are the same, either. The best machinists develop longstanding relationships with tooling manufacturers, and are able to depend on their input and recommendations. Micro 100, for example, has manufactured the industry’s highest quality turning tools for more than 50 years. Further, its tool holder offering includes multiple unique styles, allowing machinists to determine the product that’s best for them.

lathe tool holder next to micro 100 tool product packaging
Pro Tip: Be sure to take into consideration the machine’s horsepower and maximum feed rate when determining running parameters.

Bonus: Common Turning Speeds and Feeds Application Terminology

Vc= Cutting Speed

n= Spindle Speed

Ap=Depth of Cut

Q= Metal Removal Rate

G94 Feedrate IPM (Inches Per Minute)

G95 Feedrate IPR (Inches Per Revolution)

G96 CSS (Constant Surface Speed)

G97 Constant RPM (Revolutions Per Minute)

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.

Size comparison chart with square miniature end mill, ant leg, human hair, and grains of salt
Size Comparison for Harvey Tool’s #13901 Square Miniature End Mill

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 with miniature end mills
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).

burr formation mechanism using a miniature end mill
Figure 2: Burr formation mechanism using a miniature end mill 

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 End Mill

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 With Miniature End Mills

Try to minimize runout and deflection as much as possible when micromachining with miniature end mills. 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.
side-by-side view of two end mills comparing variable pitch versus non-variable pitch
Figure 3: Variable pitch tool (yellow) vs. a non-variable pitch tool (black)

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.

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.

properly selecting a spindle

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:

Haas spindle horsepower and torque chart
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.

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. These are unique due to their 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 tool that has a hole in the middle and teeth on the outer diameter. Used in conjunction with an arbor, this tool 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 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 saws. Jewelers Saws have a high tooth count enabling them to cut tiny, precise features, and Slitting Knives have 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

slitting saw terminology chart

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. Non-Ferrous slitting saws have fewer teeth, allowing for aggressively deep depths of cut.

harvey tool slitting saw

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, this tool should never be used with construction tools such as a table or circular saw.  Brittle saw blades 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.

Machining Precious Metals

Precious metals can be particularly difficult to machine due to their wide range of material properties and high cost if a part has to be scrapped. The following article will introduce these elements and their alloys as well as provide a guide on how to machine them effectively and efficiently.

About the Elements

Sometimes called “noble” metals, precious metals consist of eight elements that lie in the middle of the periodic table (seen below in Figure 1). The eight metals are:

  1. Ruthenium (Ru)
  2. Rhodium (Rh)
  3. Palladium (Pd)
  4. Silver (Ag)
  5. Osmium (Os)
  6. Iridium (Ir)
  7. Platinum (Pt)
  8. Gold (Au)

These elements are some of the rarest materials on earth, and can therefore be enormously expensive. Gold and silver can be found in pure nugget form, making them more easily available. However, the other six elements are typically found mixed in the raw ore of the four metals they sit below on the periodic table: Iron (Fe), Cobalt (Co), Nickel (Ni), and Copper (Cu). These elements are a subset of precious metals and are generally called Platinum Group Metals (PGM). Because they are found together in raw ore, this makes mining and extraction difficult, dramatically increasing their cost. Because of their high price tag, machining these materials right the first time is incredibly important to a shop’s efficiency.

periodic table with a box around the 8 precious metals

Figure 1: Periodic table with the 8 precious metals boxed in blue. Image source: clearscience.tumblr.com

Basic Properties and Compositions of Precious Metals

Precious metals have notable material properties as they are characteristically soft, ductile, and oxidation resistant. They are called “noble” metals because of their resistance to most types of chemical and environmental attack. Table 1 lists a few telling material properties of precious metals in their elemental form. For comparison purposes, they are side-by-side with 6061 Al and 4140 Steel. Generally, only gold and silver are used in their purest form as the platinum group metals are alloys that consist mainly of platinum (with a smaller composition of Ru, Rh, Pa, Os, Ir). Precious metals are notable for being extremely dense and having a high melting point, which make them suitable for a variety of applications.

Table 1: Cold-worked Material Properties of Precious Metals, 4140 Steel and 6061 Aluminum 

material properties of precious metals in relation to 6061 and 4140

Common Machining Applications of Precious Metals

Silver and gold have particularly favorable thermal conductivity and electrical resistivity. These values are listed in Table 2, along with CC1000 (annealed copper) and annealed 6061 aluminum, for comparison purposes. Copper is generally used in electrical wiring because of its relatively low electrical resistivity, even though silver would make a better substitute. The obvious reason this isn’t the general convention is the cost of silver vs. copper. That being said, copper is generally plated with gold at electrical contact areas because it tends to oxide after extended use, which lowers its resistivity. As stated before, gold and the other precious metals are known to be resistant to oxidation. This corrosion resistance is the main reason that they are used in cathodic protection systems of the electronics industry.

Table 2: Thermal Conductivity and Electrical Resistivity of Ag, Au, Cu, and Al 

thermal conductivity of silver, gold, copper, and aluminum

Platinum and its respective alloys offer the most amount of applications as it can achieve a number of different mechanical properties while still maintaining the benefits of a precious metal (high melting point, ductility, and oxidation resistance). Table 3 lists platinum and a number of other PGMs each with their own mechanical properties. The variance of these properties depends on the alloying element(s) being added to the platinum, the percentage of alloying metal, and whether or not the material has been cold-worked or annealed. Alloying can significantly increase the tensile strength and hardness of a material while decreasing its ductility at the same time. The ratio of this tensile strength/hardness increase to ductility decrease depends on the metal added as well as how much is added, as seen in Table 3. Generally this depends on the particle size of the element added as well as its natural crystalline structure. Ruthenium and Osmium have a specific crystal structure that has a significant hardening effect when added to platinum. Pt-Os alloys in particular are extremely hard and practically unworkable, which doesn’t yield many real-world applications. However, the addition of the other 4 PGMs to platinum allow for a range of mechanical properties with various usages.

Table 3: PGM material properties (Note: the hardness and tensile strength are cold worked values) 

pgm material properties

Platinum and its alloys are biocompatible, giving them the ability to be placed in the human body for long periods of time without causing adverse reactions or poisoning. Therefore, medical devices including heart muscle screw fixations, stents, and marker bands for angioplasty devices are made from platinum and its alloys. Gold and palladium are also commonly used in dental applications.

Pt-Ir alloys are noticeably harder and stronger than any of the other alloys and make excellent heads for spark plugs in the automobile industry. Rhodium is sometimes added to Pt-Ir alloys to make the material less springy (as they are used as medical spring wire) while also increasing its workability. Pt and Pt-Rh wire pairs are extremely effective at measuring temperatures and are therefore used in thermocouples.

Machining Precious Metals

The two parameters that have the most effect when machining are hardness and percent elongation. Hardness is well-known by machinists and engineers across the manufacturing industry as it indicates a material’s resistance to deformation or cutting. Percent elongation is a measurement used to quantify material ductility. It indicates to a designer the degree to which a structure will deform plastically (permanently) before fracture. For example, a ductile plastic such as ultrahigh molecular weight polyethylene (UHMWPE) has a percent elongation of 350-525%, while a more brittle material such as oil-quenched and tempered cast iron (grade 120-90-02) has a percent elongation of about 2%. Therefore, the greater the percent elongation, the greater the material’s “gumminess.” Gummy materials are prone to built-up edge and have a tendency to produce long stringy chips.

Tools for Precious Metals

Material ductility makes a sharp cutting tool essential for cutting precious metals. Variable Helix for Aluminum Alloy tools can be used for the softer materials such as pure gold, silver, and platinum.

variable helix square aluminum end mill from harvey tool

Figure 2: Variable Helix Square End Mill for Aluminum Alloys

Higher hardness materials still require a sharp cutting edge. Therefore, one’s best option is to invest in a PCD Diamond tool. The PCD wafer has the ability to cut extremely hard materials while maintaining a sharp cutting edge for a relatively long period of time, compared to standard HSS and carbide cutting edges.

harvey tool pcd diamond square end mill

Figure 3: PCD Diamond Square End Mill

Speeds and Feeds charts:

speeds and feeds chart for precious metals

Figure 4: Speeds and Feeds for precious metals when using a Square Non-ferrous, 3x LOC

speeds and feeds chart for precious metals with a pcd end mill

Figure 5: Speeds and Feeds for precious metals when using a 2-Flute Square PCD end mill