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Micromachining: What to Know About Toolholders, Drills, End Mills, and CNC Machines.

9/21/2021

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About the author: Jack Burley, Vice President of Sales and Engineering and Big Kaiser Precision Tooling Inc.
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.
Big Kaiser considers tools with <3mm to be micro tools with unique geometric considerations.
Big Kaiser considers tools with <3mm to be micro tools with unique geometric considerations.
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.
Much of this burden falls on the holder. Balance doesn’t change as spindle speed increases, however the forces it creates increase exponentially alongside speed. The impacting results appear quickly in micromachining.

When runout occurs, the edge most affected takes over the bulk of the cutting. Uneven wear causes the tool to fail more quickly than if the tool rotates about the centerline as intended. In one customer application, we found that drilling into a steel workpiece 0.590" deep with a 0.118" diameter carbide drill in a holder with 0.00008" runout accuracy produced 2,300 holes.
BIG KAISER HSK-E32, E25, or E20
Micro milling machines, ideally suited for small tools and small workpieces, are characterized by spindle speeds of more than 50,000rpm using small HSK tool holders such as HSK-E32, E25, or E20.
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.
Super-chilled CO2 or cryogenic machining with liquid nitrogen are considered possible replacements. Protecting small holder parts at the nose from coolant has always been a concern, but using gas requires more attention for holders to be effective.
Mega Micro Coolant Nut for Mega Micro Chuck 6S
The Mega Micro Coolant Nut for Mega Micro Chuck 6S provides a more efficient coolant supply for micro cutting tools and is designed for high-speed micro machining up to 6mm.
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
Big Kaiser hydro- clamping tool holder system for Swiss-type lathes
Matching medical components to each patient demands flexibility. This hydro- clamping tool holder system for Swiss-type lathes would make the decades-long approach of using ER collets obsolete by making it possible to perform a simple drill change on a gang slide in seconds.
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.

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10 Tips for Improving Tool Holder Performance

8/19/2021

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10 Tips for Improving cnc rotary ToolHolder Performance
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. 

1. Balance holders as a complete assembly

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.

2. Holder damage can go from bad to worse quickly

 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. 

3. The rule of thumb on holder dimensions

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

4. Rigidity can harm tapping operations 

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.

5. Balancing is crucial to five-axis machining

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. 

6. Consider spindle speed requirements when choosing between shrink-fit and hydraulic holders 

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.

7. Don’t overlook the tool’s effect on holder performance 

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.

8. Not all dual-contact tooling is the same

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.”

9. You may have a BIG-PLUS spindle and not even know it

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.

10. Use positive offsets during holder setup 

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. 

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UPDATE ON LIVE TOOLING

7/21/2021

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A REVIEW OF THIS MACHINING METHOD, THE BASIC CONCEPTS AND SOME EXCITING DEVELOPMENTS IN THE TECHNOLOGY
by Preben Hansen, President, Platinum Tooling Technologies Inc.
Picture
Universal style adjustable tool might be the ideal solution for families of parts.
Live tooling, as a component on a lathe, is specifically manipulated by the CNC to perform various milling, drilling and other operations while the workpiece is being held in position by the main or sub spindle. These components, whether BMT or VDI, are also called driven tools, as opposed to static tools, that are used during turning operations. All live and static tools are built per the machine tool builder’s specification for each of the various models they produce. A key to running a successful job shop or production department is to partner with a supplier who can meet the tooling needs for all or most of the machines on your floor.
combination of taper roller bearing and spindle bearings are best for live tool rigidity
Most often, live tooling is offered in standard straight and 90º angle head configurations with a wide range of tool output clamping systems, including ER collet chuck, arbor, Weldon, Capto, whistle notch, hydraulic, HSK, CAT, ABS and a variety of custom or proprietary systems developed by the many suppliers to the industry.

When the need arises for a new machine tool, careful consideration should be made to determine which live tools are appropriate for your application. While a standard machine tool package will help you get started, it is important to anticipate job and volume changes, as well any unforeseen machining challenges from the beginning, in order to avoid machine downtime. This short article is meant to give you a set of parameters to consider when evaluating the live and static tooling to use in your shop or production department. Simply stated, you need to do as much evaluation of your process, when determining the proper tooling to be used, as you did when you evaluated the various machines available for purchase. This fact is often overlooked and that can be a critical error, in the long run.

Your examination can range from the simple (external vs. internal coolant, for example) to the sublime (adjustable or multi-spindle configurations) to the custom tool, that may be required and built to suit your special application. Finding a supplier who has an in-house machine shop for the preparation of special tools is a great value-add.

Tool life is the product of cutting intensity, materials processed, machine stability and, of course, piece parts produced. Two seemingly identical job shops can have vastly different tooling needs because one is automotive and one is medical, or one specializes in the one-off and low-volume work, while the other has a greater occurrence of longer running jobs. The totality of your operation determines the best tooling for the machines being purchased.

Bearing construction and the resulting spindle concentricity drive the life of any tool. You might find that just a 10-15% greater investment in a better design can yield both longer lasting cutters and consistently superior finish on your products. Of course, the stability and rigidity of the machine tool are always critical factors. Bevel and spur gears that are hardened, ground and lapped in sets are best for smooth transition and maximum torque output. Taper roller bearings are consistently superior to spindle bearings in live tool milling applications, so look for a combination system to get the highest rigidity possible. Also, look for an internal vs. external collet nut, so the cutting tool seats more deeply in the tool, as superior performance will result.

Muliti spindle tool brings improved cutting capacity to your lathe lvie tooling
Likewise, high pressure internal coolant might be desirable. Look for 2000 psi capabilities in 90º tools and 1000 psi in straight tools.You need to ask another question, namely, is the turret RPM sufficient to handle the work to be done? It’s possible that a live tool with a built-in speed increaser, often called a speed multiplier, would be helpful. Would it be beneficial to move secondary operations to your lathe? Gear hobbing can be accomplished in this manner, as can producing squares or flats, through the use of polygon machining. 

Standard live tooling most often is best suited to production work, where the finish, tolerances and cutter life are critical, while quick-change systems may be better suited to the shop producing families of products and other applications where the tool presetting offline is a key factor in keeping the shop at maximum productivity. It’s a given in our industry that when the machine isn’t running, the money isn’t coming.
This opens the discussion of long-term flexibility and it’s the most often overlooked consideration in buying live tools. You might ask, what work do you currently have in the shop and what work will be coming in the future?

The overall economies of a changeable adapter system on your tooling may be a consideration not often made when your focus is centered on the machine being purchased.

Internal clamping nut seat the cutting tool closer to the bearing live tooling
Dedicated tools for large families of products may often be desirable for some applications, but do consider whether a flexible changing system would be more appropriate. Talk to your tooling supplier for the various options, before making that determination.
​
If standard ER tooling is suitable for the work, there are many good suppliers. It is important though, to pay 
close attention to the construction aspects noted above. For a quick-change or changeable adapter system, there are fewer suppliers in the market, so seek them out and be sure they can supply the product styles you need for all your lathe brands.
Heimatec BMT cross working live tool
Now, an application example showing clear evidence of the value of testing live tool performance...

One company was performing a cross-milling
application using an ER 32 output tool on a Eurotech lathe, running 10 ipm at 4000 rpm. They were making three passes with a cycle time of 262 seconds and were having difficulties with chatter on the finish, while producing 20,000 pieces per year. The annual cost of the machining was over $130,000. By using an alternative live tool with an ER 32AX output, internal collet nut design, with the same parameters, they were able to produce the part in a single pass with a smooth finish and cycle time of just 172 seconds. Over the course of the year, this yielded a cost savings of $45,000, approximately 20x the cost of the tool. The bottom line is the bottom line, as the accountants tell us.

In the end, you may not need a universal adjustable tool or a multi-spindle live holder or even a quick-change adapter system but do consider all these options. Talk to your machine builder and several tool suppliers, plus the most important people in this equation, your shop personnel, as their input is invaluable to keeping you up and running in a profitable, customer-satisfying scenario.

The author welcomes questions, comments and additional input from readers. Please contact Preben Hansen at 847-749-0633 or phansen@platinumtooling.com. Mr. Hansen has over 30 years in tooling and is considered a leading authority on the topic in the North American machine tool market.
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Installing a Sub-Plate setup with mPower SpeedLoc.

6/11/2021

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mPwer Sppedloc
Here is a very helpful video on 'how-to' setup a subplate with SpeedLoc by mPower.
  1. Install the Locators though the subplate into the receivers finger tight
  2. Use a Precision Straight edge to span the locator shanks
  3. Use an indicator to to "tap in" the subplate to align with machine table
  4. Complete the X -Axis and then do the same for the Y-Axis
  5. Recheck the X-Axis

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INDICATION MARKS ON PULL STUDS ​IS NOT NORMAL

5/25/2021

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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.
Picture
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.

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Metalcutting Circular Saw Cutting Recommendations, Tips, Tricks & Troublshooting

4/13/2021

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compiled & edited by Bernard Martin
Martindale Gaylee Carbide HSS Saw Selection troubshooting tips tricks
As more and more of our customers are using Martindale Gaylee Circular saws we put together this guide to the commonly asked questions such as "Is there a rule-of-thumb for the number of teeth?" or "How much side clearance should I have?" Here we cover a lot of the fundamentals of selecting the right circular saw blade configuration, some tips, tricks, and troubleshooting for when things go wrong. 

Circular Saw Feed Rates

These are general cutting speed recommendations for circular saws used in metalcutting from Martindale/Gaylee. The may vary from application to application but are basically some general suggestions starting parameters when using high speed or carbide saws. 
  • HSS Saws: .002”-.006”  (IPT-inch. per tooth / CLPT-chip load per tooth)
  • Carbide Saws: .0002”-.0015”  (IPT -inch. per tooth / CLPT - chip load per tooth)
This is a conservative recommendation as a starting point for feed rates, and may vary depending on material being cut and cutting speed (SFPM).

Selecting the Proper Number of Teeth in Your Metalcutting Saw

Generally speaking, deep cuts and soft material require fewer teeth for chip clearance and stronger teeth (landed).

Thin material requires more teeth, but keep-in-mind that at least 2 teeth on the blade need to be engaged in cut. Hard materials and narrow slots (under .025”) likewise require more teeth.

Hard Materials require more teeth, and  give a smoother cut,  but at a much lower production rate.  ​

Alternately beveled teeth keep chips from sticking in the cut and in the tooth gullets.

And Remember that there should be at least 2 teeth engaged in the cut at all times.
Increase Number of Teeth For:
  • Thin material 
  • Thin cuts under .025”
  • Slow spindle speeds
  • Hard material
  • Sand castings 
  • Thin castings 
  • Work hardened materials
  • Known inclusions or Hard spots 

Decrease Number of Teeth For:
  • Free cutting material​
  • Soft Gummy long chipping materials.
  • Deep cuts (over 1/4”)
  • High speeds Machining Applications
Picture
  • Chip clearance and tooth strength (Consider Metal Slitting or Copper Slitting style saws.)

Rake Angles and Side Clearance Angles

RAKE ANGLES
​Just as in an end mill or a band saw blade, a rake angle is the term used to describe the direction of the blade’s teeth, as referenced from the rotation and central axis of a saw blade. If you imagine a line going from the exact center of the blade to each tooth, having the front of the tooth directly on that line would be a zero degree rake angle. The rake angle of the blade is described in comparison to that imaginary line.

A positive rake angle meana that the teeth are angled more towards the angle of rotation, while a negative rake angle would mean that they are angled backwards, away from the direction of rotation. Generally speaking, the preferred rake angle is:
  • 5° to 10° positive for other soft materials.
  • 5° negative for yellow brass
  • On center for steel.

SIDE CLEARANCE (Tangential Clearance Angle)
This is also known as dish or hollow grind.  You measure down the side of the tip and the difference it is the difference between front and back.  As you cut, material it gets compressed and springs back after the cutting edge passes.

​A steep side clearance angle gives plenty of room for the material to expand and prevents thermal expansion of the base material.  Keep in mint that a very flat side clearance angle can provide a smoother cut in some materials.  For stainless steel and tenacious metals such as copper, zinc, tin or lead an increase in the side clearance is desirable as these materials tend to "spring back" (thermal expansion) on the blade. 
Why do Circular Saws Break?

Why do Circular Saw Blades Break?

It's commonly known that when saw thickness is less than 0.125″, keyways can cause stress risers and cracks.  That is why washers are often used.  However, Breakage, Wobble and Rubbing problems are often caused by how the washers are mounted on either side of saw. 

Remember, washers drive the saw in the absence of a drive key. They must always be clean, flat and bur-free. A speck of dirt will let saws wobble and cut oversize. 

If a saw breaks, it may score the washers. Always check for scoring marks around saw hole for dirt, chips or grit.  Shiny spots, as small as a pinpoint, indicate that chips where imbedded under washers.

Circular skid marks indicate the nut was not tight.

Generally speaking:
  • Thin saws should especially be supported by washers as large as possible.
  • Washers must be of equal diameter or they will flex out saw dish and cause one side of saw to rub.
  • The nut must be wrench-tight.

Saw Blade Teeth most often break as a result of:
  • Too high a feed rate.
  • Spindle bearings are worn.
  • Drive belts  are loose or sheaves worn.
  • Improper tightening: If saw blade pauses momentarily in its rotation while feed advances, it WILL break.
  • Workpiece indexed before the saw has cleared the slot.
  • Improper workholding - The workpiece not tight or not well supported.
  • Saw is dull, even the best tools do eventually wear out.

NOTE: HSS saws will turn colors as they heat during cutting. A straw color is the limit. The saw will lose its temper when it starts turning blue.
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To Balance, Or Not To Balance? Toolholders, That Is

3/16/2021

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DEPTH OF CUT COLUMN
by Jack Burley, President and COO at BIG KAISER Precision Tooling Inc.
It’s time for machine tool builders and machining companies to shelf the long-standing ISO 1940-1 standard in favor of ISO 16084:2017. Not only is balancing tools rarely necessary, it can also be risky.
A lot of conflicting information has circulated over the years about balancing tools. As an author of the new standard for calculating permissible static and dynamic residual unbalances of rotating single tools and tool systems – ISO 16084:2017 – allow me to clear some things up and, hopefully, make life a little easier for you.
An argument can be made for balancing almost every tool put in a machine. In the world of rotating tools, small changes to an assembly, like a new cutting tool, collet, nut or retention knob, can put an assembly out of tolerance.

​Therefore, it stands to reason that any unbalance could translate to the part, tooling and/or machine spindle in harmful ways. You’ll hear the case for balancing every single tool based on the 
long-standing ISO 1940-1 standard.
over-balanced-tool-holder
Balancing a toolholder several times causes the toolholder to become excessively modified. It's OVERBALANCED
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.
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.

A Little Lesson About Forces

This all begs the question: When do you need to take the time to balance holders? I would argue that tools require balancing only if they’re notably asymmetrical or being used for high-speed fine finishing. Here’s a rule I’ve long followed: If cutting forces exceed centrifugal forces due to unbalance, high-precision balancing isn’t needed because the force required to balance the tool will most likely be less than cutting forces.
In other words, if you’re rough milling with a heavy radial cut, the different forces will start bending the tool. When that happens, the cutting forces and all the feed forces will be substantially higher than whatever the unbalance forces might be. If that’s the case, it’s not that you take the unbalance force and add it to the cutting force and find your adjustment. 
Big Kiaser New Baby Chuck and Mega New Baby Chuck are balanced for High speed machining
Big Kiaser New Baby Chuck and Mega New Baby Chuck are balanced for High speed machining. The Precision collet is guaranteed to produce a maximum runout of only 1 micron at the collet nose.
At that point, aggressive cutting – not unbalance – is going to damage the spindle.  

Unbalanced tools are also blamed for issues that turn out to be misunderstandings about a machine’s spindle. I’ve visited shops with new high-speed spindles that had trouble running micro tools over 15,000 RPM. They rebalanced all the tools on the advice of their machine tool supplier, but to no avail.  It turned out the machine was tuned for higher torque and higher cutting forces. Before going to the effort of balancing toolholders, work with your machine builder to understand where a spindle is tuned.

Not only is balancing tools rarely necessary, it can also be risky. Our inherently asymmetrical fine-boring heads are a good example. Because we balance them at the center, a neutral position of the work range, you lose that balance if you adjust out or in.

To adjust, you’d typically add weight to the light side, which can be a problem for chip evacuation and an obstructor. Or you can remove weight from the heavy side, but that means you have to put some big cuts on the same axis of the insert and insert holder, ultimately weakening the tool.

In longer tool assemblies, common corrections made for static unbalance can also cause issues. It happens when a toolholder is corrected for static unbalance in the wrong plane; i.e., adding or removing weight somewhere on the assembly that’s not 180 degrees across from the area where there’s a surplus or deficit.

​Once the tool is spun at full speed, those weights pull in opposite directions and create a couple unbalance that often worsens the situation.
BIG KIASER Mega ER Balanced holders
All the components of Big Kaiser's Mega ER Grip Series - Body, Collet and Collet nut - Are all balanced for high speed machining

A Cautionary Tale

If you do go down the balancing road, you’d better know where you can modify tools, what’s inside, how deep you can go, and at what angles. Whether you’re adding or removing material on a holder, I highly recommend consulting the tool manufacturer for guidance first.

As a cautionary tale, consider a customer who was attempting to balance a batch of our coolant-fed holders. Based on the balancing machine, the operator drilled ¼-inch holes at the prescribed angle into the body of the holders. Not realizing what was inside, he drilled into cross holes connecting coolant flow and ruined several holders.

Tooling manufacturers are doing their part to avert disasters like this. For most, simple tools like collet chucks or hydraulic chucks are fairly easy to balance during manufacturing. We account for any asymmetrical features while machining and grinding holders and pilot each moving part, ensuring they’ll locate concentrically during assembly. These measures ensure the residual unbalance of the assemblies is very, very low and eliminate the need for balancing.
Auto-balancing boring heads are designed specifically for the high-speed finishing I mentioned earlier, where unbalance force can be greater than cutting force. Our EWB boring heads, for instance, have a small internal counterweight that moves in direct proportion with each adjustment. Because the weight is carbide, it’s three times more dense than the steel in the tool carrier and is maintained inside the head’s symmetrical body.
Picture
Autobalance boring heads, Series 310 EWB, maintain perfect balance throughout the work range due to the integrated counter-balance mechanism. Even at maximum speeds, balanced tools guarantee vibration-free boring, resulting in increased productivity and high precision.
Decades of the same standards have conditioned us to think a certain way about balancing tools. While it seems logical that every tool must be balanced, it’s just not the case: Many issues attributed to unbalance aren’t caused  by unbalance, and the risks of balancing every single tool often aren’t worth the reward.
​
Save your balancing time and resources for high-speed fine finishing. If you do have work where balance is crucial, consider how the tools you buy are balanced and piloted out of the box and/or consult your partners before making any modifications.
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Don't Take Your Retention Knobs for Granted

2/16/2021

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​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. 
1 Retention knob pull stud casues of failure

Retention knobs go through thousands of tool changes which means that they are subjected to the very high pulling forces from the spindle’s drawbar.

This force can be up to 2300 ft. lbs. for 40 taper toolholders and up to 5000 ft. lbs. for 50 taper toolholders.
​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. 

METAL FATIGUE: WHY THEY FAIL

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 threads on your retention knob will stretch slightly when load is applied and the loading borne on each thread is different.

When you apply a tensile load on a threaded pull stud, the first thread at the point of connection sees the highest percentage of the load.
Percentage of Load on a Retention Knob Thread
Percentage of Load on each thread of a Retention Knob.
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.

​RETENTION KNOB DESIGN

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?  ​
For the same reason we put corner radiuses on end mills, sharp corners are a common area of failure for any mechanical device.

​The same holds true with your pull studs:  The sharp angles on the head of the retention knob and at the minor diameter of the threads are common locations of catastrophic material failure.
Retention Knob Metal Fatigue
These are the two weakest points of any 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.
Styles of Retention Knob for Rotary Toolholders
Styles of MegaFORCE Retention Knobs

MATERIAL

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 VS. CUT THREADS

5. Cut thread vs rolled thread retention knob
A cut thread, image 1, has a higher coefficient of friction due the the cutting process, while a roll formed thread, image 2, has a lower coefficient of friction which means that it engages deeper into the toolholder bore when subjected to the same torque. You will notice that Cutting threads tears at the material and creates small fractures that become points of weakness that can lead to failure. Rolled threads have burnished roots and crests that are smooth and absent of the fractures common in cut threads.
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%.  
6. LMT Fette - Thread rolling with F2 Rolling head on CNC lathe
Shown here is a Fette head cold forming a thread. Note how the three roller forms center and maintain near perfect concentricity of the pull stud shaft.
In cold forming, the thread rolls are pressed into the component, stressing the material beyond its yield point. This causes the component material to be deformed plastically, and thus, permanently.

There are three rollers in the typical thread rolling head that maintain better concentricity by default than single point cutting of the threads.

Also, unlike thread cutting, the grain structure of the material is displaced not removed.
Rolled threads produce grain flows that follow the contour of the threads making for a stronger thread at the pitch diameter which is the highest point of wear. 

The cold forming process also cold works the material which takes advantage of the nickel work hardening properties of 8620.
7. Fette Turning Concepts Thread Rolling Magnaflux
Photo courtesy Mike Roden at Fette Tool. www.turningconcepts.com
By comparison, cut threads interrupt the grain flow creating weak points.

MEGAFORCE GEOMETRIC DESIGN

MegaForce Retention Knob features vs standard pull stud
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.
Blended Radii
With the new Techniks MegaFORCE pull studs, stress risers of sharp angles have been eliminated through the blended radii on the neck where the gripper engages under the head of the pull stud.
9. Techniks MegaFORCE Pull Studs
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.
MegaFORCE Technical Specs
  • Material: SAE8620
  • All knobs are case carbrized, hardened, and tempered to:
    • Case depth: 0.025” – 0.030”
    • Surface hardness: HRc 56-60
    • Core hardness: HRc 44 minimum
Torque Specs
The following are the guidelines for torquing your pull studs according to Techniks.
  • BT 30 36 ft. lbs.
  • ISO 30 - 36 ft. lbs.
  • 40 taper - 76 ft. lbs.
  • 50 Taper - 100 ft. lbs.

RETENTION KNOB BEST PRACTICES

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.
  • Regularly inspect retention knobs for signs of wear. Wear may appear as dimples or grooves under the head or visible corrosion anywhere on the retention knob. 
Picture
  • If the retention knob demonstrates any signs of wear replace it immediately
  • Make sure to properly torque the retention knob to the manufacturer’s specifications. Use a torque wrench and retention knob adapter to ensure proper torque. 
  • Overtightening can overly stress the retention knob leading to premature failure and can cause the tool holder taper to swell leading to a poor fit between the machine spindle and the tool holder.
  • Apply a light coat of grease to the retention knob MONTHLY to lubricate the drawbar. If you use through-spindle coolant (TSC), apply grease to the retention knobs WEEKLY.

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