End mill stickout amount from collet - opinions

pMetal · Jun 3, 2020

I was wondering how far you typically like to have your end mills stick out beyond the collet face.

I typically set the tools in as far as possible, with the flutes starting just outside of the collet, so I have the shortest stickout possible. I do this because I am looking for the most rigid setup possible. I mill stainless almost exclusively, so I am always looking for greater rigidity.

But, the short stickout often creates challenges with getting coolant to the tool since the collet nut acts as an "umbrella" to block coolant.

I often see pictures online of endmills sticking out quite a bit from their collet or toolholder. For example, on a 3/8" endmill, I'll often see the tool sticking out 3/8" to 1/2" beyond the minimum location that I usually use. That extra stickout probably would help with coolant delivery.

In your experience, does the extra stickout make much of a difference?

DavidScott · Jun 3, 2020

I think it makes a difference but so does the extra coolant and chip evacuation. I am not as worried about how far the tool sticks out as I used to be. I think tool holder projection is a bit more important. I think a tool diameter past the flutes doesn't affect how much it cuts as much as how much of a bump it can survive, like a shifted part.

One more thing. Sidelock holders about the best for stiffness and getting coolant to the tool, so far the more I use them the more I like them.

gkoenig · Jun 3, 2020

It is all a balancing act depending on what you need to do, because there is an ideal setup that we need to compromise as the situation dictates.

That ideal is obviously a tool with a flute length that exactly matches the depth of cut, with those flute ends sticking out only about 0.010" from the holder face, and going into a cut that is flooded with coolant from 360 degrees of coverage at all times.

Unless you're setting up a production part being made in high 5 figure quantities, you are never going to actually make that ideal happen, so you compromise all the time.

mhajicek · Jun 3, 2020

IMHO the best case is a shrink fit thru-coolant holder with 1000PSI TSC. When I'm not using the shrink fit I'll use an ER collet and run the TSC through the collet. Minimum stickout in both cases. If you don't have TSC you're handicapped and have to make do.

exkenna · Jun 3, 2020

Projection is everything. The shorter, the better.
It’s one of the basic principles of metal removal.

Milland · Jun 3, 2020

This is a neat slow motion video of an endmill side cutting. It's from Lyndex-Nikken, trying to sell their milling chucks, but it also graphically shows the reaction of chips coming off the flutes and their interaction with coolant or air blasts.

YouTube

What I see (and I'm open to having my interpretation challenged) is a upward motion of the chip as it separates from the stock, but it's then pushed down (and if slot cutting, back into the slot) by the orientation of the air blast.

So it's not just a matter of flute length and position within the collet that counts for cutting stability and chip clearing, it's also whether your coolant/air is aimed to most effectively clear chips from the cutting path and not fall back into slots or whatever (start at 20 seconds in).

I would argue that for good chip clearing I'd want a little more of the flute lenght exposed above the part top, to allow as much clearance in the gullet of the cutter to promote continued raising and removal of the chip. If your collet face hits the rising chip and pushes it back down, I think it's too close, all other things being equal.

Further in the video other cutter geometries (fast helix) are shown giving the chips a real kick up and out.

exkenna · Jun 3, 2020

A tapered core is what causes the classic rooster tail of chips.
Great fun to watch

Milland · Jun 3, 2020

exkenna said:
A tapered core is what causes the classic rooster tail of chips.
Great fun to watch

And I was skipping through the video and didn't notice til later it was not an air blast, but some other feature that was redirecting the chips, either the runout of the gullet or the underside of the collet.

Eh, still interesting to watch.

Mike1974 · Jun 4, 2020

exkenna said:
Projection is everything. The shorter, the better.
It’s one of the basic principles of metal removal.

Not necessarily...

Point in case. Setup sheet had 2" projection called out for a 1/2" endmill. Setup guy grabbed a 2" LOC endmill and set it up. Ran like dog shit, squealing and carrying on. I looked at it and said "I don't remember it sounding like this", turns out only needed 1"LOC with 2" projection. Switched it up and sounded fine and ran the job good. So really, projection AND LOC can make a difference. If you are just cutting .5" at a time or so, a stubby endmill hanging out of the collet an extra 1" will cut much better than a 1.5" LOC hanging out full LOC.... if that makes sense (more flute = less rigid)

Cole2534 · Jun 4, 2020

Mike1974 said:
Not necessarily...

Point in case. Setup sheet had 2" projection called out for a 1/2" endmill. Setup guy grabbed a 2" LOC endmill and set it up. Ran like dog shit, squealing and carrying on. I looked at it and said "I don't remember it sounding like this", turns out only needed 1"LOC with 2" projection. Switched it up and sounded fine and ran the job good. So really, projection AND LOC can make a difference. If you are just cutting .5" at a time or so, a stubby endmill hanging out of the collet an extra 1" will cut much better than a 1.5" LOC hanging out full LOC.... if that makes sense (more flute = less rigid)

Operator increased effective stickout by selecting a tool of the correct length, but reduced section, and experienced chatter issues. Doesn't this verify Curtis' point?

It's just beam deflection, but with a complicated beam. Fixed on one end, distributed load on the other. He chose the correct length beam, but it was of insufficient section.

Mtndew · Jun 4, 2020

I always stub it up to the flute washout unless I need more reach.

DavidScott · Jun 4, 2020

Wait until you are trying to get over the 4th axis and under the collet nut to clear the chips in a deeper slot, then that extra stick out is most desirable. As long as you can clear the chips then shorten it up as much as possible, balancing act.

DMF_TomB · Jun 4, 2020

pMetal said:
I was wondering how far you typically like to have your end mills stick out beyond the collet face.

I typically set the tools in as far as possible, with the flutes starting just outside of the collet, so I have the shortest stickout possible. I do this because I am looking for the most rigid setup possible. I mill stainless almost exclusively, so I am always looking for greater rigidity.

But, the short stickout often creates challenges with getting coolant to the tool since the collet nut acts as an "umbrella" to block coolant.

I often see pictures online of endmills sticking out quite a bit from their collet or toolholder. For example, on a 3/8" endmill, I'll often see the tool sticking out 3/8" to 1/2" beyond the minimum location that I usually use. That extra stickout probably would help with coolant delivery.

In your experience, does the extra stickout make much of a difference?

.
law of the universe, stickout endmill 2x more and deflection increases 2x2x2 or 8x more deflection
3x more stickout its 3x3x3 or 27x more deflection
.
it you reduce stickout 0.7 its previous amount it deflects .7x.7x.7 or .34 (about 1/3 previous deflection)
reduce stickout .9 (90%) of previous amount its .9x.9x.9 or or .73 (deflection about 73%)
.
i have seen through spindle coolant where coolant comes out of the collet slots, often for heavy duty end milling its not in a collet, set screw holders (weldon shank) tend to limit movement amount, where as a collet end mill can move much more. carbide endmills can be bought with weldon shank flat but its usually not always standard like HSS mills are

kazlx · Jun 4, 2020

I've been running SK (Maritool) holders more and and more. Also sizing down a little to decrease the size of the holder. ER32 is great for flexibility, but even with a 1/2 or 3/8 tool in there, there's still just a big nut in the way. Running an SK16 has been way better. Smaller, smoother nut, which makes it easier to direct coolant for the tools doing the heavy lifting. I've been trying to just buy 'better' holder setups for tools I use frequently. I do also try to set the tool as close as I can.

Delw · Jun 4, 2020

A side lock holder would be better for rigidity and coolant access why not go with that?
I personally think collet holders are over rated and switched back to sidelocks especially on harder metals and also small endmils. I get better run out with them and have no coolant issues getting to the endmill /part even in small slots.
I am assuming you got long shank endmills and your collet is holding on more than 75% of its length

CarbideBob · Jun 5, 2020

DMF_TomB said:
.
law of the universe, stickout endmill 2x more and deflection increases 2x2x2 or 8x more deflection
3x more stickout its 3x3x3 or 27x more deflection
......

Good advice but not quite right.
Don't want to be picky but it is two connected beams.
One is the cross section of the fluted area which is more "flexible" than the shank itself.
This is why you want the shortest possible flute length that will do your cut.
Same cut, same stick-out but different flute lengths gives different results.
Bob

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End mill stickout amount from collet - opinions

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