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."

With this innovative centering tool from Big Kaiser, spindles and tools can be centered quickly and easily.  It's ideal for limited spaces within small lathes.  The Centering Tool is a static dial gauge for easy centering.

• Reduce setup time
• Centering the tool holder is simplified since the dial gauge position is static and in front
• Easy setting with a fine adjustment mechanism
• Magnetic base allows for flexible mounting positions

Check out the technical video below to learn how to get center on your CNC Lathe.

Precision Cutting Tools already holds one of the highest tolerances on shank diameter in the industry for their end mills.  All PCT End Mills Shanks hold an h6 tolerance! That means that 
1/8" - 1/4": -0.0001"/-0.0003"
1/4" - 1/2": -0.0001"/-0.0003"
1/2' - 1": -0.0001"/-0.0004"

A tighter grind tolerance often times will mean a much shinier polished shank.  A polished shank is more apt to have lower coefficient of friction which makes it more prone to slip particularly while being held in a collet type toolholder.  

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

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

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

Since the introduction of the XT Series 4 flute, 5 flute and the new 279 series 4 flute ball nose end mills they have proven to be a huge success in the machining of Titanium and stainless steels.   These tools have already made their impact in the machining of many other areas such as all steels and super alloys.
 
MA Ford's spotlight focus is on some other materials that are widely used in the market.  17-4 PH stainless many feel is somewhat difficult to machine and performance may vary depending on the material hardness.  That is not the case with the new XT series end mills.  These tools do not seem to care what hardness is presented to them!  28-42 RC is primary range for this series of stainless steel.  

Example: A customer had a very difficult 17-4 PH medical component with lots of contouring both roughing and finishing.  A 1/2" 279 Series was used for roughing the profile at 600 SFM with a depth of .015 and .025 step over at 80 IPM.  The customer had to double the speeds and feeds as well as increase the step over to get the desired finish required!

The 277 Series 4 flute can full slot up to 1X dia. depth at speeds as high as 260 to 340 SFM. The chip loads will be lighter than profile milling dependent on the tool diameter and fixture set up. The slotting depth can be increased even beyond 1X depth (which generally requires a reduction in speeds and feeds).
 
The 278 Series 5 flute can slot up to 1X depth effectively but slotting is more suited for the  4 flute 277 Series if a lot of slotting is to be done.  The speeds and feeds are the same as the 277, but calculations must be made for the additional cutting edge.  It is not recommended to slot over 1X the tool diameter with this 5 flute tools as it is best suited for profile milling both conventional and high speed machining.
 
The new 279 Series 4 flute ball nose end mill is an excellent choice for both conventional and high speed machining of stainless steels.  With the added radial relief and a thicker cross section in the center of the tools it can withstand extreme speeds and feeds both roughing and contouring. 

NTK's industry leading line of ceramic cutting tools recently expanded with new solid CERAMIC end mills! You can see our product announcement here: NTK now offers SX9 Ceramic End Mills for Cutting Exotic Alloys which contains the various features. Below is the  technical info on how to run the NTK Ceramic End mills and a troubleshooting guide.  

NTK's SX9 cermaic end mill grade can run at speeds of 2000 SFM. The line-up includes 4 and 6 flutes in inch and metric versions. Again, you can learn more about on our Blog Post.  

As with any other techncial questions please get in touch with us on our CONTACTS page and we can provide both over-the-phone troubleshooting or schedule at time for on-site techncial training.

...and here's the segment from "How It's Made" that covers the more general principles of making a HSS end mill.  You can see that OSG has a more advanced process for their carbide end mills.

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.

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.