Larger endmills pulling out of R8 collet

keeena

keeena

H-M Supporter - Gold Member
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I feel like every time I run a larger endmill (5/8"-3/4"): it inevitably will start pulling out of the R8 collet. My most recent case was side-milling 2" thick steel. Endmill this time was a 3/4" YG rougher 3" long. I was running a 0.200" RDOC, 230RPM, 1.5IPM. These might be somewhat conservative numbers; FSWizard suggested 560RPM and 3.5IPM -> fz 0.0016in/th (my numbers have the same chip load). The milling is on a Alliant knee mill. The milling otherwise went perfectly fine; machine wasn't straining at all, chips looked great.

I tried 2 different collets (one was brand new Shars "precision" collet); both behaved the same. This has happened both when manually torquing the DB or with my power drawbar. I run my power drawbar at 90 psi (op range is 80-100psi) and the mfr recommends impacting for 3sec once collet is seated. I typically let it dwell for 1.5-2sec. I did test at 100psi and 3sec; no help. Interestingly, at one point this wedged the collet in tight enough that the power drawbar couldn't push the collet out. Instead it sheared off the threads on the drawbar. I had to give the EM a tap sideways to dislodge it. It was not caused by the alignment pin jacking up the slot in the collet...the collet simply was wedged in there that tight.

The bore in the spindle feels fine; no burrs or dings. But I haven't tried bluing it.

Am I expecting too much or should this type of cut / load not be pulling the EM out? Anything else I can try?

I realize I could use a ER or Weldon type adapter, but was avoiding adding length and potential runout to the setup. I did eventually swap to the ER40 and no sliding issues there.
 
Sounds like the RPMs were too low . Also , make sure the end mill and collet are completely oil free when installing .
 
mmcmdl said:
Sounds like the RPMs were too low . Also , make sure the end mill and collet are completely oil free when installing .
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Do you mean both RPM and feed? Or just RPM relative to the feed (i.e. reduce the chip load / fz)?
 
Second on end mill holders for large end mills. Also if they do not already have a notch, grind one to seat your set screw on.

I use CNC and CAN NOT have the end mill slip. So, I use end mill holders when ever possible.
 
keeena said:
Do you mean both RPM and feed?
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Not knowing what steel , SS could be from 100 to 500 . 400 rpms would be a safe starting spot . .002 chip load maybe . You want that tool cutting and not rubbing . As MW said , end mill holders are best when hogging . Make sure you lock the end mill in the down position on the screws also or it will/can pull down .
 
My buddy as an apprentice was cutting a large keyway in a Worthington Pump shaft on a large DeVlieg Jig Mill . Had it mounted in an end mill holder but it did pull out and scrapped the shaft . Lesson learned .
 
mmcmdl said:
My buddy as an apprentice was cutting a large keyway in a Worthington Pump shaft on a large DeVlieg Jig Mill . Had it mounted in an end mill holder but it did pull out and scrapped the shaft . Lesson learned .
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I don’t think this is a story about tool holding. Then again maybe the word apprentice don’t mean the same thing to others.
I’ll bet on an end mill holder over an apprentice any day though.
 
mmcmdl said:
My buddy as an apprentice was cutting a large keyway in a Worthington Pump shaft on a large DeVlieg Jig Mill . Had it mounted in an end mill holder but it did pull out and scrapped the shaft . Lesson learned .
Click to expand...
Must have not been a Weldon type tool holder with the set screw set properly?
 
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