Technical Blog courtesy of Techniks USA
​Edited and amended by Bernard Martin

If you work in the metalcutting, signmaking or cabinet making manufacturing industry, the term “collets” is already very familiar to you.

​There are many types of collets used in many different industries and applications. This article is focused on collets used in rotary tool holders found in CNC milling machining centers and CNC Routers and also used in CNC Lathes and Swiss Style CNC's. 
​
 Let's cover the basics:

Collets are the critical connection between the cutting tool and the tool holder, also called a collet chuck. Most collets are round, cone-shaped, and slotted. Collets encircle the cutting tool shank to evenly distribute holding power around its center bore.
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Before getting too deep into the technical aspect of collets, It's going to be helpful to anyone new to the use of collets to understand the basic anatomy of collets and of a collet chuck system.

The tapered collet base is made to fit into the collet pocket of the collet chuck body. The free release locking tapered (16°included, 8° per side) design of the collet base and collet pocket allows the collet to be centered in the pocket as it is pushed in by the collet nut on the lead face during setup.

This centering effect enables the collet to achieve a high degree of accuracy (concentricity); much more than drill chucks and side-lock style end mill holders.

As he collet nut is tightened down on the collet, it is pushed into the pocket collet chuck pocket.  The slots in the collet allow the I.D. bore to collapse and apply clamping pressure to the cutting tool shank. It's essentially a spring that is compressed tight around the shank of the cutting tool such as a drill or end mill.

​The result is a very strong and rigid clamping force on the cutting tool. Since the collet base is tapered to match the collet pocket, tool runout (T.I.R.) is reduced.

Total indicator runout (TIR) is a term often used in manufacturing, especially when dealing with rotating parts such as cutting tools, particularly endmills and drills. TIR is defined as the difference between the maximum and minimum values measured across an entire rotating surface about a reference axis.

The ER Collet Fixtures provide a simple and low profile solution for clamping cylindrical workpieces using the same technology you are already familiar with in your rotary toolholders.

It’s been estimated that a tool with a run-out of 50% of the tool’s chip load will reduce its tool-life by 40%.

That means that a 1/8” tool with a 0.00019” chip load per tooth will lose 40% of its tool-life with a run-out of less than 0.0001”.
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Excessive and inconsistent run-out from a properly setup ER collet chuck assembly typically occurs due to friction build-up between the 30° face of the collet and the collet nut.

The result?

• Improved tool runout
• Longer tool-life
• Less frequent tool changes
• Improved surface finishes

Other Parlec P3 collet advantages:

• 3 micron T.I.R
• Fewer slots that standard collets making them more rigid – in the cut!
• Special slotting seal for coolant up to 2,000 PSI

​Don’t throw away you ER collet chucks to improve accuracy
Try Parlec P3 collets and supercharge your ER collet system.

Written and edited by Bernard Martin

One of the most important elements of the toolholding 'system' is the collet nut. Each toolholder "system" consists of a precision ER tool holder that comes with a special "Power Coated" high power nut that holds tighter than any other nuts.

According to Techniks, the 'Power Coat' nut is the secret to their high holding power. Because it holds so tight, the 'Power Coat' nut improves T.I.R., extends carbide tool life, and improves finish in heavy milling operations.

Techniks recommends that for best results always tighten the nut to the proper torque using a torque wrench with a tightening stand, and never over-tighten the nut because this can damage both the collet and the collet pocket.

To demonstrate the difference between an uncoated and coated collet nut, Mike Eneix, from Techniks did some testing.

He took an uncoated, imported nut and put it to the test against the Parlec PowerCOAT nut. Mike took them to the limit to see which one gives you more holding power.  Check out the video below!

DEPTH OF CUT COLUMN
by Jack Burley, President and COO at BIG KAISER Precision Tooling Inc.

Since its institution in 1940, the G2.5 balance specification has been widely accepted across the industry; i.e., “it’s how things have always been done.”

However, machines were much slower 80 years ago. Back then, the most advanced machines would have spun larger, heavier tools at a maximum speed of about 4,000 RPM. If you applied the math from those days to today, you’d get unachievable values.

For example, the tolerances defined by G2.5 for tools with a mass of less than 1 pound rated for 40,000 RPM calculates to 0.2 gram millimeters (gm.mm.) of permissible unbalance and eccentricity of 0.6 micron. This isn’t within the repeatable range for any balance machine on the market.

Similarly, application-specific assemblies, for operations like back boring and small, lightweight, high-speed toolholders, can’t be accurately balanced for G2.5.

Machine tool builders rely on an outdated number, too, often basing spindle warranty coverage on using balanced tools at very specific close tolerances. While it’s true that poorly balanced tools run at high speeds wear a spindle faster, decently balanced tools performing common operations won’t wear spindles or tools drastically and deliver the results you’re looking for.

Not sure which level of precision you need to order for your workholding collet? Tecnicrafts has put together this easy to understand chart that explains the difference between "standard" precision and "ultra" precision for both round stock and hex stock. The tolerance is based upon your ore size.  We hope you find this helpful! Call us with questions!

Tecnicrafts Industry is an ISO 9001:2015 Certified Company

• In the production processes, the blanks are processed carefully & inspected at each stage in order to obtain a high quality Guide Bushing or Collet.
• The Technicrafts In-house specialized Heat treatment plant ensures multi-stage processing in order to achieve best mechanical properties such as hardness, springing properties.
• Technicrafts Special Purpose machines for each process supports in achieving Best Quality output consistently.
• Technicrafts is fully aware that their products are used in critical processes across industries and commit themselves to ensure uninterrupted work flow.

Spindles and tool holders are in a constant battle with the forces of nature, with this battle becoming more and more difficult with heavier cuts and longer projections. Chattering and deflection have always been the bane of machinists’ existence, so much so that the sight of a long and slender toolholder will immediately cause goosebumps.

If you understand why a long tool holder behaves the way it does, you’ll know that there are ways to fight back against this bending. Every machinist knows that short and stubby holders are more resistant to deflection than long and slender holders. You’ve also probably heard that, if possible, you’ll want most of your cutting forces to be axial rather than radial.

Not only does this fight chatter in operations like boring, but your spindle also is better equipped to handle loads in this axis. However, these options aren’t always going to be on the table, especially in unavoidable long-reach situations and many milling operations.

In this constant battle with tool deflection, much time and effort has been spent designing shorter holders, stiffer tools, and clever anti-vibration geometry and materials. But oftentimes, the body diameter(s) of the holder can be overlooked as a means of increasing rigidity, especially in situations where it is all you have to work with. This is a serious shame, as you’ll soon discover.

The concept of dual-contact technology has been around for years, existing in many different forms but always with the same goal of capitalizing on this untapped potential of rigidity. For those who don’t know, dual contact refers to the shank contacting the spindle taper and the spindle face simultaneously.

Oftentimes, the solution involved ex post facto alterations to the spindle or tool holder, such as using ground spacers or shims to close the gap, for example. In other words, there was no standard solution, and if you wanted dual contact, you would have to be prepared to spend time and money either buying modified tool holders or modifying them yourself to adapt them to your spindle.

BIG-PLUS emerged as a solution to this issue. Essentially, both the spindle and tool holder were ground to precise specifications so that they closed the gap between spindle face and flange in unison (while depending on very small elastic deformation in the spindle). What this meant is that operators were able to confidently switch BIG-PLUS tooling in and out of a BIG-PLUS spindle and achieve guaranteed dual contact.

Not only that, but standard tooling could still be used in a BIG-PLUS spindle if necessary, and vice versa.

Though not technically an international standard, it’s been adopted by many machine tool builders because of the clear performance improvements and simplicity. In fact, BIG-PLUS spindles come standard on more machines than you would think. We often come across operators that have machines with BIG-PLUS spindles and don’t even realize it.

How exactly does dual contact help with tool rigidity? The torque (or moment) exerted by the cutting forces is maximized at the point where the holder and spindle meet, the base of the tool holder. With standard CAT40 tool holders, this would be the gage line diameter. When the holder contacts the spindle face via BIG-PLUS, the effective diameter would be the larger diameter of the v-flange, since this is the new anchoring point of the holder and spindle. So, you are beefing up the diameter at the point where the reactionary force is greatest.

It’s not too much of a leap to conclude that a larger effective diameter will give you more rigidity. That being said, you may still be asking yourself: does such a seemingly small increase in diameter really make a difference? To understand the effect of BIG-PLUS, you must understand the physics behind it.

Imagine a simple scenario in which a tool holder is represented by a cylindrical bar that is fixed at one end and free-floating at the other. In other words, a cantilever beam. If you think about it, this is essentially what a tool holder becomes once it’s secure in the spindle. Now, let’s introduce a radial force F that acts downward at the suspended end of the bar, which represents a cutting force you would encounter when milling or boring, for example. The bar, as you might expect, will want to bend downward. It’s similar to how a diving board bends when someone stands at the end, though less exaggerated.

It’s possible to predict the amount of deflection (or inversely, bending stiffness) at the end of this hypothetical bar if you know its length, diameter and material. The expression below represents the stiffness k at the end of the bar where d=diameter, L=Length and E=Modulus of Elasticity

I won’t ask you to do any math here, I just want you to look at the equation. We can see that increasing d will increase the value of k, while increasing L will decrease the value of k, since it’s in the denominator of the equation. This certainly makes sense if you think about it: a short and squat bar (large d, small L) will be more rigid than a long and slender bar (small d, large L). 

Something interesting to note is that d is raised to the 4th power, while L is only raised to the 3rd power. Diameter affects rigidity an entire order of magnitude more than the length does. This is where the power of BIG-PLUS comes from and is why a small increase in diameter can have such a powerful effect on performance.

For a CAT40 tool holder, the gage line diameter is Ø44.45 mm and the flange diameter is Ø63.5 mm. Let’s imagine two bars of identical length and material, so L and E remain unchanged. One bar has a diameter of Ø44.45 mm (standard CAT40) and the other has Ø63.5 mm (BIG-PLUS CAT40).

If you were to plug these values into the above equation for comparison, you would find that the BIG-PLUS holder results in a k value that is around 4 times greater than the standard bar. Based on this comparison, you could say that a BIG-PLUS holder is 4 times as rigid as an identical standard CAT40 holder, because it is 4 times as resistant to deflection.

Think of the tool life and surface finish improvements you would see with a tool that is 4 times more rigid, not to mention the reduction in fretting and potential for reduced cycle time. You would get similar results if you were to make the same comparison for CAT50, BT40, BT30, etc.

If you’re still not convinced, we can also compare the rigidity in this way: Let’s say there is a Ø63.5 mm BIG-PLUS CAT40 bar of some arbitrary length. One of our more common gage lengths is 105 mm, or just over 4 inches, so let’s use it as an example. 

You’re probably wondering, at what length would a comparable standard CAT40 holder have an equal stiffness? If we take our stiffness expression and set it equal to itself (one side representing BIG-PLUS, the other non BIG-PLUS), we can plug in this BIG-PLUS holder length and our known diameters to find our unknown non-BIG PLUS length:

What does this mean? A BIG-PLUS holder of around 4 inches or 105 mm in length will have equal rigidity to a standard CAT40 holder of around 2.5 inches or 65 mm in length. Any experienced machinist will know quite well the difference in rigidity between a 4-inch long holder and a 2.5-inch long holder.

If this is true, we can say that implementing BIG-PLUS is equivalent to a 40% reduction in length in terms of rigidity. Theoretically, a BIG-PLUS tool holder will behave like a standard tool holder that is nearly half of its length! 

Obviously, we’ve used simple and idealized cases here to represent the complicated and dynamic world of metal cutting. Tool holders, of course, don’t have uniform body diameters or materials and the cutting forces usually aren’t acting in one direction in a constant and predictable way. If our holder necks up and down to different body diameters along its length, which is realistically what happens, each of these sections would be its own microcosm of “beam” that would influence the overall behavior (at that point, finite element analysis on a computer becomes the only practical way to predict behavior). 

So, will the advantage of BIG-PLUS really be as dramatic as our hand-calculated classical beam theory suggests? Probably not, but it depends on the tool holder/tool. Most cases will follow our simple model quite closely in practice; others not so much. If nothing else, we’ve demonstrated how dramatically the flange contact of BIG-PLUS can influence rigidity, at least in a purely mathematical sense. 

As if you needed any more reasons to be on the BIG-PLUS bandwagon besides increased rigidity, you will also eliminate Z-axis movement at high speeds, improve ATC repeatability and decrease fretting. This means that you will take heavier cuts, scrap less parts, and increase tool and spindle life.
BIG-PLUS isn’t a new idea by any means, but with a proven track record of tackling tough jobs, it’s hard to imagine working in a modern machine shop and not taking advantage of what it has to offer.

If you’re still not convinced, we can also compare the rigidity in this way: Let’s say there is a Ø63.5 mm BIG-PLUS CAT40 bar of some arbitrary length. One of our more common gage lengths is 105 mm, or just over 4 inches, so let’s use it as an example. 

You’re probably wondering, at what length would a comparable standard CAT40 holder have an equal stiffness? If we take our stiffness expression and set it equal to itself (one side representing BIG-PLUS, the other non BIG-PLUS), we can plug in this BIG-PLUS holder length and our known diameters to find our unknown non-BIG PLUS length:

We are very excited to announce that we are now able to offer on-site technical training to YOUR machinists at YOUR location!  This is offered at no charge  to customers who use any of the manufacturer's whom we represent in California and Nevada.  

However, just because you don't purchase things from us, don't feel left out! We also offer on-site topic specter training on any of the following topics for $150/hour.  

Each presentation lasts about 2 hours.  The presentations last approximately 45-60 minutes with the remaining time for Q&A and discussion about unique applications in your facility.