Written and edited by Bernard Martin
PowerCOAT Collet Nuts provide up to a 75% increase in holding power!
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 our high holding power. Because it holds so tight, the 'Power Coat' nut improves T.I.R., extends carbide tool life, and even permits light 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!
What makes the difference?
As anyone knows who has changed a flat tire on their car, tightening down a nut on a 60 degree thread involves some friction as the mating metal surfaces interact. That's why nuts can be a bit 'hot' to the touch when you take them off. The objective with the "Power Coated" nuts was multifold:
First Techniks needed to reduce the coefficient of friction on the thread angle to enable more lubricity for the nut to tighten down farther. As we all know 'heat' causes metal to "grow" so what may at first appear to be tight, in fact, loosens, as soon as you stop tightening it.
Second they needed to make sure that the front surface of the collet that engages the shorter 30 degree taper on the front of an ER collet did not 'twist' as the night tightened down.
Both problems really involved reducing friction and through a combination of engineering tolerances and unique coating process we believe that we've found the most economical solution to eliminate the use of cheater bars and collet over torque. Here's what they've found out in testing the "Power Coated" Nuts:
“Power Coat” is an innovative, permanent coating that increases clamping pressure of the nut up to 75% compared to standard ER nuts. More holding power reduces the chance of spinning the shank of the tool inside the collet, which can cause premature failure of the collet.
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.
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.
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 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?
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 VS. CUT THREADS
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%.
Also, unlike thread cutting, the grain structure of the material is displaced not removed.
By comparison, cut threads interrupt the grain flow creating weak points.
MEGAFORCE GEOMETRIC DESIGN
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.
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.
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.
by, Bernard Martin
As carbide end mills gain higher and higher speeds and metal removal rates there has also been a trend by round tool manufacturers to tighten up the tolerances on both the cutting diameter and the shank diameter to improve concentricity. At the same time, shrink fit holders have become more and more popular because they hold a tighter concentricity as well. To achieve this both the shank and the bore now have similar surface finishes and this has led to a problem The tools pull out in the cut.
Shrink fit holders are the most accurate for TIR as the toolholder engages completely around round shank tools with a bore tolerance of -0.0001" to -0.0003". As high performance end mills have tightened shank tolerances to the same range of -0.0001" to -0.0003" they have used finer and finer grain grinding wheels which give the shanks a 'shiny' appearance.
Shiny means that the superfinished shank has a lower coefficient of friction. So, although the TIR is tighter, the shank is more "slippery". End mills traditionally had surface finish of about 8 μin on the tool shank. But that's changed. It's been recommended that tool shanks used in shrink fit holders should not have a finish finer than 16 μin. for optimum holding power, but tell that to the guy who just superfinished the end mill to a super cocncentric tolerance that you don't want it looking that good.
Everyone knows that the last thing you want is for the end mill to slip in the middle of a heavy cut or on the finishing pass of a high tolerance part. These 'hi performance' end mills, often times have higher helix angles which are great for ejecting chips but also create a higher pull out force on that slippery shank. And reducing the helix angle is not the answer.
We already know that the gripping pressure is a function of the interference between the tool shank and the shrink fit toolholder bore. Most shrink fit holders have a already bore surface finish of between 12 μin. and 16 μin. So they are ground to a very high tolerance and have about the same surface finish as the toolholder shank.
End mill manufacturers and machinist have tried a variety of methods over the years to stop the tools from pulling out. This has ranged from grit blasting the shank to rubbing chalk on the shank, but most everyone in the industry has felt that the problem really needs to be addressed by the longer life toolholder rather than the replaceable cutting tool.
That's the problem that Techniks wanted to address. Techniks claims that their "proprietary non-slip TTG594 compound virtually fuses the tool shank with the shrink fit toolholder."
ShrinkLOCKED Toolholders eliminate cutting tool pull-out and provide 4X the friction drive force compared to un-treated shrink holders.
It’s not just a rougher bore finish that enhances the holding power. TTG-594 is a compound that has a much higher Brinell hardness than carbide so it can “bite” into the tool shank. But this does not affect the ability to perform tool changes.
Techniks arrived at their 4x the holding power comes from torsion testing vs. a standard shrink fit toolholder. They used a ¾” carbide gage pin in a standard holder and found the torque at which the tool will spin in the bore.
They then tested the ShrinkLOCKED holder using the same test.
According to Greg Webb, at Techniks,
"We actually could not find the point at which the tool would spin in the ShrinkLOCKED holder as we broke the carbide gage pins at 4x+ times the torque of the standard holder. The holding power is greater, we just have not found a way to measure this, so we kept our claims conservative at 4x."
In order to get the maximum life out of your Steep taper rotary toolholders in your CNC milling machines, follow these best practices that you can implement in your shop. Perhaps not all of them can be implemented every day or every time but it's well worth being aware of how to best protect your investment.
Collet Chuck Size
We often get asked to spec out tooling packages for new CNC mills and one of the questions we encounter most, or should, is how do you select the right toolholder collet size for your companies applications? The real choice is in the size of the collet chuck itself. So several considerations should be reviewed...
What size are your tools?
Your first consideration should be the size of end mills or drills you will be using most often. If you are doing smaller work you would require smaller diameter range collets. Generally you may prefer the ER16 and ER32 sizes.
If the bulk of your tool requirements are in the mid range you can also use the ER20. The following is a list of tool diameters that can be used with each size collet chuck. Essentially, the most popular, and again, readily available from a number of sources, are the ER 16, ER20, and ER32... in no particular order.
How far do you need to reach?
A second consideration is the actual reach of the tool. Not projection reach, also know as “gage length” "l1" but projection diameter “D”.
Obviously, stubbier is better for projection reach "L1". But, you also need to review the families of parts that you intend to run on the machine.
If you intend to use the holder to "reach" into a tight fit then the OD of the projection "D" of the toolholder needs to be considered.
Many shops don't always consider this and end up using much longer carbide shanked end mills to get into deep pockets when getting a smaller diameter ER collet and collet chuck would be much less expensive over the life of the job.
Here is a list of the OD projection diameters:
Sometimes there is just no getting around having a custom tool made. Give us a call at 916.765.4227 or email us if you just can't seem to reach into the part with your toolholder.
by Bernard Martin
ER, IT’S IN THE DETAILS
The ER collet system has several advantages when using today's CNC computerized milling machines. The most significant advantage is flexibility to hold any type of round shank tool.
An ER collet can be used in drilling, reaming, and tapping as well as milling applications just by exchanging the collet. Its accuracy also provides greater tool life than older style collet systems like TG or DA.
Another advantage is the flexibility of the collet for clamping a wide range of tool shanks with a small number of collets. ER 16 through ER 40 provide a collapse range of ~.039" flexibility for clamping cutting tools. This is a benefit for you because you will not have to carry as many collets in inventory for the different jobs you need to do each day.
The ER collet also provides more holding power by using two principles.
In addition to mechanical differences, the ER collet is also user friendly. It is a self-extracting collet, which eliminates the need for collet squeezers to extract the collet by any other means than screwing the nut off. This enables the operator to spend time running the machine, not extracting collets.
These basic principles allow the ER collet system to be the most widely accepted collet system in the world for holding round shank cutting tools.
ER style collet chucks should be used for the bulk of your needs. They are the most dependable, with the least runout, both in and out of the cut, are readily available (so the prices continue to drop) and will give you the best tool life out of the lot of them.
Advantages of the ER Collet System
by Bernard Martin
We often run end mill "tests" to determine which tool performs best. Obviously, our goal is to "win' the test and get more business for our manufacturer's. This is article is about one our "tricks" and it's also why we represent both cutting tool manufacturers and rotary tool manufacturers. We want to make sure that the products work together.
As a general rule most cutting tool & tolholder manufacturers prefer to use single angle (ER/DR style) collet chucks for general purpose cutting tool applications under 1/2" (12mm).
The rules are a bit different in High Speed Machining, as there are many more things to consider, but the problems of TIR at high speeds, where you can hear and feel the chatter, are still there in general end mill cutting operations at lower RPM.
It's all boils down to runout and uneven chip load.
Our technical section is written by several different people. Sometimes, it's from our team here at Next Generation Tooling & at other times it's by one of the innovative manufacturer's we represent in California and Nevada.
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