Larger endmills pulling out of R8 collet

[keeena]

Today I had issues with a 1/2" EM slowly working its way out, so I did a poor mans marker blue-up on a nearly new Shars 3/4" collet.





So...it looks like I have a bit of a problem; I should be getting a lot more taper contact. I'll be giving a few other sizes a try. Is there anything else worth trying or inspecting? There are a couple of light groves in the bore but it feels very smooth; no burrs. The locating pin isn't dragging on the collect.

What's the going rate on a spindle re-grind? Or worth trying a quality collet to see if that's the problem?

 

[Smithdoor]

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 .

Greedy
Does not pay to be greedy.
If want take a big cut a horizontal mill does better job. It take a cut with speed.

Dave

 

[markba633csi]

Your spindle taper does not look healthy to me- maybe that's where the problem lies

 

[keeena]

This is the pattern with a solid R8 shank (not a collet):


I did try with a few other collets, both the new Shars as well as some older collets in various sizes. Some had a bit better contact but none looked remotely good as the solid shank. All of the collets were making contact near the nose.

 

[OTmachine]

The picture that you shared previously showed a Lot of EM length engagement, and would have a Lot of pulling force for an R8 or any other collet type holder. I suggest rethinking your game plan to take smaller depth of cut. Also, Hogging end mills require different speeds and feeds than regular end mills dependent on material being machined, & make and style of cutters.

 

[keeena]

The picture that you shared previously showed a Lot of EM length engagement, and would have a Lot of pulling force for an R8 or any other collet type holder.

I'm having issues even with much smaller DOC & WOC.

But yes: the pic in the first post was a 2.25" DOC, 0.100" WOC with a 3/4" rougher EM. The resulting load (motor, feed) seemed very reasonable, so I never would've expected that this type of cut wouldn't be possible.

 

[akjeff]

I'm having issues even with much smaller DOC & WOC.

But yes: the pic in the first post was a 2.25" DOC, 0.100" WOC with a 3/4" rougher EM. The resulting load (motor, feed) seemed very reasonable, so I never would've expected that this type of cut wouldn't be possible.

You may have a bad batch of Chinese collets? That solid R8 tool looked like it blued up much better. I can't say that I've ever had an end mill of any size slip, and have taken some pretty healthy cuts. Any chance of borrowing a collet from a friend to see if it repeats?

 

[Parlo]

A couple of things may be worth checking.
Is the collet 5/8" or 16mm?
Is the tool shank 5/8" or 16mm?
They are almost the same but mixing them would show with the blue.

I always have the quill fully retracted when milling - quills for drills as they say.
I never rely on the quill nut / circlip combination for preventing the quill from pulling down.
Perhaps you have a combination of the above?

Here is a video showing a simple solid stop system.

 

[keeena]

@Parlo - thanks for your suggestion. Yes: the collets and EMs are definitely both imperial and I even mic'd the EMs just to be sure.

The quill is not moving, its the EM working its way out of the collet. DRO for Z doesn't budge at all. And yes, ideally I have the quill retracted all the way or as much as possible given what I'm doing. Its not issues of rigidity - the cut otherwise is great.

 

[Parlo]

@Parlo - thanks for your suggestion. Yes: the collets and EMs are definitely both imperial and I even mic'd the EMs just to be sure.

The quill is not moving, its the EM working its way out of the collet. DRO for Z doesn't budge at all. And yes, ideally I have the quill retracted all the way or as much as possible given what I'm doing. Its not issues of rigidity - the cut otherwise is great.

There used to be R8 collets & drill chuck jaws with an etched finish to increase grip. Mostly used in drill chucks to grip hardened shanks, I haven't been able to find any collets online though.

I have used an etching pen with tungsten electrodes on the inside of cutting dies to grip slugs & prevent them pulling back, perhaps using an etching pen on the cutter shank would increase grip. See Hoffmann 085600 & 085620.

Otherwise try shot blasting the shank.