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.

By John Zaya, Product Specialist, BIG DAISHOWA—Americas

As the title implies adjusting screws, also known as back-up screws, stop screws and preset screws, are not just a simple set screw. They are a screw with a purpose--three actually.

The first is to provide a fixed stop for a cutting tool to rest against during tool changes. This allows an operator to save time as they do not have to pull out a ruler, setting jig, etc. to reassemble the cutter into a holder.

A secondary purpose of the adjusting screw is to assist the tool holder in keeping the cutter from being pushed up into the holder if the cutting loads increase to the point where the tool may slip up into the holder.

​The third is to offer sealing for coolant-through tools. ​

When an old cutter is swapped out and a new one put in its place, the repeatability of this process will vary based on a few parameters such as cleanliness and the OEM cutting tool overall length tolerances.

Cleaning the clamping bore or collet of a holder provides better runout repeatability which should be old news to everyone, but if old coolant and contaminants are not removed, they would get jammed between the end face of the shank and the adjusting screw, affecting the length setting. 

Cutting tool overall length tolerances may also vary from one OEM to another. We have seen them range from ±.3mm to ±.5mm (±.012” to ±.019”). Others may be tighter or looser.

​Most modern machining centers come with tool length offset measurement systems which will provide the final precise gage length of a tool assembly. With the rough position provided by the adjusting screw, the machine operator can continue working and does not need to worry about tool clearances and stick outs. 

The clamping mechanism of the holder also affects the length repeatability. Both hydraulic chucks and milling chucks are radial clamping systems, whereas a tapered collet is drawn down into a taper by a threaded nut. This draw down causes the cutter to be drawn down as well.

​For this we have two types of adjusting screws: HMA/HDA solid type and NBA rubberized type. The solid type is a one-piece steel construction part, whereas the rubberized type has a rubber padded conical pocket that absorbs the axial travel of the cutter shank as the collet is clamped. 

Milling chucks also have a second type of adjustment screw option that can be built into the back end of a reduction sleeve. As cutting tool diameters get smaller, the length of the shank also gets shorter.

​As such, the end face of the shank may not reach the HMA adjusting screw when installed it the body of the holder. The AC Type Collet adjuster screws into the back end of the reduction sleeve where the shank the tool can easily be reached. 

It is always recommended to consult the tool holder catalog or technical documentation to ensure that a holder can support an adjusting screw. Some holders are very short or have very deep internal features that may not allow for the use of any adjusting screw. In those cases, a depth setting ring or collar on the shank of the cutting tool may be an acceptable alternative. 

Caution should be used on shrink-fit holders. Thermal expansion/contraction occurs in all three axes, so as the body of a shrink-fit holder cools down it will draw the cutter down jamming onto the adjusting screw. This could lead to damage to the screw, the holder or the cutter. 

Put simply, the manufacturing process of boring is enlarging a hole in a piece of metal. There are quite a few different pieces of machinery or approaches that can be used to make holes from lathes and mills to line boring or interpolation. We wanted to do a quick break down of the different kinds of boring tools available to bore holes and/or secondary boring operations.

Boring deep holes can involve extreme length-to-diameter ratios, or overhang, when it comes to tooling assemblies. Since it can be difficult to maintain accuracy and stability in these scenarios, we need boring bars to extend tooling assemblies and while maintaining the rigidity to make perfect circles with on-spec finishes.

Solid boring bars
Typically made of carbide for finishing or heavy metal for roughing, solid boring bars have dense structures that make for a more stable cut as axial force is applied.

Damping bars
When cutting speeds are compromised, or surface finishes show chatter in a long-reach boring operation, damping bars are an option. They have integrated damping systems. Our version, the Smart Damper, works as both a counter damper and friction damper so that chatter is essentially absorbed.

Boring heads are specifically designed to enlarge an existing hole. They hold cutters in position so they can rotate and gradually remove material until the hole is at the desired diameter.

Rough boring heads
Once a bore is started with a drill or by another method, rough boring heads are the choice for removing larger amounts of material. They are built more rigid, to handle the increased depths of cut, torque and axial forces needed to efficiently and consistently make the passes to remove materials.

Fine boring heads
Fine boring heads are best used for more delicate and precise removal of material that finishes the work the rough boring head started. They are often balanced for high-speed cutting since that’s the best approach for reaching exact specifications.

Twin cutter boring heads
Most boring heads feature one cutter that cuts as its feed diameter is adjusted by the machine. There are twin cutter boring heads that can speed up cutting and add versatility. For example, the Series 319 and other BIG KAISER twin cutter boring heads include two cutters that can perform balanced or stepped cutting without additional accessories or adjustments by switching the mounting locations of the insert holders that have varied heights.

Digital boring heads
Traditionally, adjusting boring heads has been painstaking and time-consuming, especially when it’s done in the machine. It’s easy to make mistakes when maneuvering to read the diameter dial and adjusting it to the right diameter. Digital boring heads have a LED that makes precise adjustments much easier.

Since cutters are on diameter of boring heads and not their face, they are not able to initiate a hole on a flat surface or raw material. Especially in smaller bores, fluted drills called starter drills can be used to get the hole started before rough boring.

Specialty boring heads
Back boring and face grooving heads, as well as chamfering insert holders, are available for some of the most common secondary operations, after a hole is bored. We produce specific heads with cutters at the appropriate angles so each of these operations can be done without manually moving the part, changing the tool or adjusting the cutter angle.

Modular boring tools
Since limiting length-to-diameter ratios is so crucial to boring success, it’s extremely valuable to be able to make your tooling assembly as short as possible. Our modular components are based on a cylindrical connection with radial locking screw that allows for the ideal combination of different kinds of shanks, reductions and extensions, bars, ER collet adapters and coolant inducers.

Looking for some help finding the right boring equipment for your next job or new machine? Our engineers are here to help. Get in touch with us here.

Micromachining, cutting where the volume of chips produced with each tool path is very small, is not a high-speed operation in relation to chip load per tooth. Rather, it involves a high spindle speed relative to cutter diameter. The part may be physically larger, but details of the part require ultra-small profiles achieved only by micromachining. In other words, micromachining is not limited in scope to only miniature parts.

TOOLHOLDING
In medical work, where tight tolerances are standard, dynamic runout; the measurement of the spindle at high speeds, performed using laser or capacitance resistance technology, and balance must be controlled to deliver and maintain viable tool life.

A holder with 0.00060" runout accuracy produced nearly two-thirds fewer holes, only 800. In this scenario, the shop could save hundreds of dollars a month in carbide costs – as well as labor costs due to less tool changing – by making one smart tool holder choice.

Holder attributes that can boost production include symmetrical design, a perfectly concentric collapse of the collet around the cutter, and a ball-bearing raceway nut with precision-ground threads.

CHALLENGES
While these characteristics are good rules of thumb, things change fast in this field and, like our customers, we must adapt as trends emerge.

Batch sizes are getting smaller. Bone screws, for example, were typically run on multi-axis, Swiss-type lathes where the same tools and programs ran for days at a time. Traditionally, prototyping in this arrangement was not an option because of the complexity and time involved in programming and setup. Today’s need for customized sizes demands flexibility and quick changeover to remain productive.

We are investing a large portion of our research and development (R&D) in tackling this challenge. We are working on hydro-clamping tool holder systems that could make the decades-long approach of using ER collets obsolete. It would make it possible, for example, to perform a simple drill change on a gang slide in seconds.

COOLANTS
Another trend in medical manufacturing being driven by the U.S. Food and Drug Administration (FDA) is clean machining without the use of water-soluble coolants.

We are focusing on two features:

• Holders that remain completely sealed to outside atmosphere
• Very small delivery holes in collet faces or clamping nuts that properly restrict gas flow
  

TOOLING
Tool considerations also must be taken into account to keep up with the demanding medical field. Better results often cannot be achieved by simply increasing spindle speeds or using smaller tools; a deeper understanding of cutters is necessary.

We consider tools with diameters <3mm to be micro tools. These aren’t simply smaller versions of their macro counterparts. They have geometric considerations all their own. For example, the 1mm Sphinx drill can run at 80xD. But this is only possible because the cylindrical shaping extends further down the tool, closer to the tip, to facilitate pecking and maintain strength.

Tool carbide should be ultra-fine grain (nano or submicron grain size) to ensure high abrasion resistance and good toughness. Coatings are valuable too, but it’s important to understand how coatings can negatively impact micro tool performance. Micro tools have extremely fine surface finishes and sharp cutting edges. Coatings can fill in valuable space – a flute on a drill, for example – needed for proper chip evacuation, which is critical in these applications.

Coatings must be ultra-thin (<1µm) and smooth; our experience shows that misapplied coatings result in poor tool life due to breakage; the coating reduces cutting edge sharpness, increasing torque force on the drill. When coating is necessary, consult with the cutting tool manufacturer to provide this directly.

Chips and small tooling naturally do not get along well. Compensating for low spindle speeds with tools that have more flutes support an ideal feed rate, but chip evacuation may suffer. Determining the appropriate chip load – as close to the cutting edge as possible – allows operations at the highest possible spindle speed, accelerating the cycle and improving surface finish.
Optimal conditions exist when the chip load is relatively equal to the cutting edge radius.

Many micro end mills are designed so the cutting edge radius has a positive rake angle to create a shearing action. A chip load less than the cutting edge radius often results in a negative rake angle where the tool rubs rather than cuts. This increases the force required and generates more heat which can result in built-up edges and poor tool life. A chip load significantly bigger than the cutting edge radius often leads to premature failure because the tool is not robust enough to withstand such forces.

MACHINE TOOLS
Micromachining requires machine tools with very high sensitivity, fine resolution in the feed axis, and very precise spindles capable of high speed with low dynamic runout. For micro-drilling operations, specialized micro machines are best.

Micro milling machines are suited for small tools and small workpieces. They are characterized by spindle speeds faster than 50,000rpm using small HSK tool holders such as HSK-E32, E25, or E20. With the right holder, tool runout can be controlled to less than 1µm (0.000040") at the cutting edge, ensuring sub-micron accuracy.

In medical micromachining, understanding each piece of the equipment puzzle is critical. It’s also important not to make assumptions based on other tools or parts you may have worked with, especially in more standard sizes. Invest the right time and energy in gearing up for the next medical job and you’ll get more parts done right faster.

The four critical requirements for tool holders are clamping force, concentricity, rigidity, and balance for high-spindle speeds. When these factors are dialed in just right, there’s nearly no chance of holder error and considerable cost reduction is achieved thanks to longer tool life and reduction of down-time due to tool changes. 

Easier said than done, our experts shared some of their best, quick-hitting advice for top tool holder performance in different situations. 

Long-reach milling has some unique demands; when setting up this type of job, always balance tool holders as a complete assembly. While many tooling providers pre-balance their holders at the factory, it’s often inadequate, especially for long-reach applications.

 Wear and tear on holders can be costly in the end, but there are ways to protect against it. Inspect and care for your holders. Trauma on a holder or spindle—dings, scratches, gouges, etc.—can magnify quickly. One bad holder can spread its problems like an illness. If you’re seeing disruptions like these on your holders, get them out of the rotation. 

Looking for affordable ways to avoid vibration? Start by opting for a holder with a combination of the largest diameter and shortest length possible.

What many don’t realize about tapping operations is that a perceived strength of collet chucks—their rigidity—can actually be detrimental. Rigidity does very little to counteract the dramatic thrust loads imposed on the tap and part, exacerbating the already difficult challenge of weathering the stop/reverse and maintaining synchronization.

Five-axis machining introduces a whole new set of tooling challenges. While important in any type of machine, balance may be of most importance in full five-axis work. A well-balanced holder helps ensure the cutting edge of the end mill must be consistently engaged with the material in order to prevent chatter and poor surface finish quality. 

If you have to choose between shrink-fit and hydraulic holders in a long-reach application, consider the spindle speed required. If a hydraulic chuck exceeds its rated RPM, fluid is pulled away from the holder’s internal gripping gland, causing loss of clamping force. But when used within its recommended operating range, a hydraulic tool holder offers superior runout and repeatability. On average, a good shrink-fit holder has about 0.0003-inch runout, while a hydraulic chuck offers 0.0001 inch or better.

The cutting tool affects holding ability more than most machinists and engineers realize:

1. Polished shanks reduce friction, as does the cleanliness.
   
2. Oil and coolants reduce gripping power.
3. Cutter shank roundness is often assumed to be close enough to perfect to ignore, but in reality, a 25 millionths tolerance is necessary for high-speed performance.

Anyone in the market for BIG-PLUS dual-contact tooling should consider this simple statement: Only a licensed supplier of BIG-PLUS has master gages that are traceable to the BIG grand master gages and have the dimensions and tolerances provided to make holders right. Everyone else is guessing and using a sample BIG-PLUS tool holder as their own master gage—a practice that any quality expert will advise against.

Look for the marking: “BIG-PLUS Spindle System-License BIG DAISHOWA SEIKI.”

You’d be surprised how often we hear from our certified regrinders or engineers in the field about folks that didn’t realize their machine had a BIG-PLUS spindle—the message can get lost in the supply chain or during the sales process. 

The easiest way to know if an interface is BIG-PLUS is to place a standard tool into the spindle and see how much of a gap there is between the tool holder flange face and spindle face. Without BIG-PLUS, the standard gap should be visible, or about 0.12 in. If it is BIG-PLUS, the gap is half of this amount, or only 0.06 in. These values change depending on 30 taper, 40 taper or 50 taper sizes, but the gap is visibly less than usual.

It may be how it’s traditionally been done but touching off holder assemblies in each machine to establish negative tool offsets based on the zero-point surface—the vise, machine table, workpiece, etc.—is not the most efficient process. We think the choice is pretty clear: adapting machines to a single presetter so they can receive positive gage lengths is superior to using all types of machine-specific negative offsets. 

This is a change to “the way things have always been done” that can be met with some resistance, but in the grand scheme of things, it’s a relatively small and simple step that makes life much easier. It’s a relatively low-cost opportunity to introduce more standardization of holder setup to the shop floor.

Holders are the bridge between the machine and the part. That’s a lot of pressure—literally and figuratively. It’s important to select, care for and use holders carefully from the day they are purchased until they’re tossed into the recycling bin. 

From collet chucks to coolant inducers, BIG KAISER is North America’s source for standard-bearing tool holders that guarantees high performance. Explore the full lineup. 

by Bernard Martin
There have been some who claim that drawbar gripper fingers and/or ball marks that appear on retention knob head after several tool changes is normal.

It is NOT.  
​THAT IS FALSE. ​

According to Haas CNC, ball or gripper marks on the edge of the pull stud indicate that the drawbar does not open completely.

​If you see these indication marks you should check your drawbar and replace these pull studs immediately.

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.

​by Bernard Martin
Retention Knobs are the critical connection between your machine tool and the tool holder and they are the only thing holding a steep taper tool holder in the machine’s spindle.

​Techniks has recently introduced their MegaFORCE retention knobs that have some rather unique features when compared to standard pull studs.  Before delving into the features of the MegaFORCE pull studs, let's review some things that you may not know, or think about, on a daily basis. 

​According to Haas, you should expect a service life of about 6000-8000 hours for a retention knob.  

​Most all rotary toolholder manufacturers state that you should be replacing your pull studs at least every three years.

However, if you're running multiple shifts, 24-7, making lots of tool changes, making very heavy cuts with long reach or heavy cutting tools, and/or have ball lock style grippers instead of collet type grippers used on the retention knob, you will probably need to replace your studs at least every six months.

Given the spindle speeds that we are running at to remain competitive, retention knobs are not an item that you want to take a chance on breaking.  I can tell you firsthand that 5 pound toolholder with a drill in it flying out of the spindle at 23,000 RPM is not something you want to experience. 

Pull studs encounter catastrophic failure as a result of metal fatigue. The metal fatigue can be caused by a number of reasons including poor choice of base material, engineering design, machining process, poor heat treatment, and, sometimes, they have just met or exceeded their service life. We're going to dig into each of these reasons below but first let's look at some threading fundamentals.

The load on each subsequent thread decreases from there, as show in the table. Any threads beyond the first six are purely cosmetic and provide no mechanical advantage. ​

Additional threads beyond the sixth thread will not further distribute the load and will not make the connection any stronger. 

That is why the length of engagement of the thread on a pull stud is generally limited to approximately one to one & a half nominal diameter. After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession.

Repetitive cycles of loading and unloading subject the retention knob to stress that can cause fatigue and cracking at weak areas of the pull stud.

What are the weak areas of a standard retention knob?  ​

The most common failure point for a retention knob is at the top of the first thread and the underside of the pull stud where the grippers or ball bearings of the drawbar engage and draw the toolholder into the spindle.

Remember, bigger Radii are stronger than sharp corners. ​More on that soon.

Not all retention knobs are made from the same material, however, material alone does not make for a superior retention knob. Careful attention to design and manufacturing methods must be followed to avoid introducing potential areas of failure.

Techniks MegaFORCE retention knobs are made from 8620H. AISI 8620 is a hardenable chromium, molybdenum, nickel low alloy steel often used for carburizing to develop a case-hardened part. This case-hardening will result in good wear characteristics.  8620 has high hardenability, no tempering brittleness, good weldability, little tendency to form a cold crack, good maintainability, and cold strain plasticity.

There are some companies making retention knobs from 9310. The main difference is the lower carbon content in the 9310. 9310 has a tad more Chromium, while 8620 has a tad more nickel.  Ultimate Tensile Strength (UTS) is the force at which a material will break. The UTS of 8620H is 650 Mpa (megapascals: a measure of force). The UTS of 9310H is 820 Mpa. So, 9310H does have a UTS that is 26% greater than 8620H.

​That said, Techniks chose 8620 as their material of choice because of the higher nickel content.  Nickel tends to work harden more readily and age harden over time which brings the core hardness higher as the pull stud gets older. The work hardening property of 8620 makes it ideally suited for cold forming of threads on the MegaFORCE retention knobs.

​It should be noted that some companies are using H13. H13 shares 93% of their average alloy composition in common with 9310. 

Rolled threads produce a radiused root and crest of the thread and exhibit between a 40% and 300% increase in tensile strength over a cut thread. The Techniks MegaFORCE retention knobs feature rolled threads that improve the strength of the knob by 40%.  

By comparison, cut threads interrupt the grain flow creating weak points.

Overall Length
There are some claims that a longer projection engages threads deeper in the tool holder preventing taper swelling. While a deeper thread engagement can help prevent taper swelling, applying proper torque to the retention knob is an effective way to reduce taper swelling.

An over-tightened retention knob may still cause taper swelling regardless of how deep it engages the threads of the tool holder. Additionally, the longer undercut section above the threads presents a weak point in the retention knob.

Ground Pilot
There is a ground pilot, underneath the flange, which provides greater stability. The pilot means the center line of the tool holder and pull stud are perfectly aligned.

Magnetic Particle Tested
Each Techniks MegaFORCE retention knob is magnetic particle tested to ensure material integrity and physical soundness. MegaFORCE retention knobs are tested at 2.5X the pulling forces of the drawbar.

In order to maximize the life of your retention knob and prevent catastrophic failure here are some technical tips to keep your shop productive and safe.

Special thanks for Greg Webb at Techniks and Mike Roden from Fette Tools/ Turning Concepts, for providing technical insights.