endmill problems

[hammers-n-nails]

im having trouble keeping my endmills in the collets. when i do a heavy cut the endmill gets pulled down out of the collet a bit, sometimes a few thou sometimes 1/4" before i realise it, this has led to more than one good bit of metal going to the scrap pile. i especially notice this on 3/4" endmills but have had it happen with smaller ones too. if i scratch up the shank of the endmill with emery cloth a bit and clean out the collet and shank with laquer thinner to get every bit of cutting fluid off or just torque the piss out of the drawbar i can get them to hold that way but it seems like there ought to be an easier way. any suggestions? thanks in advance

zach

 

[va4ngo]

Have you tried cigarette paper wrapped around the circumference of milling cutter?

Phil

 

[Ken Bartlett]

Unless your taking light cuts, an end mill in a collet is bound to spin. Use of end mill holders, which utilize a setscrew tightened against the flat on the end mill shank is preferred. No chance of slippage with this method. Although I must admit, especially on the smaller X3/X2 mills where z axis height is limited, using end mill holders gives you less room and rigidity.

 

[NickG]

I've never had an end mill slip in my er collets but they have a range of sizes they clamp on.

Finger collets only work with the size it's designed for but you should get enough clamping force to stop it spinning. Really stupid question but are you using the right sized collet for the end mill?

 

[Stan]

I only use MT3 collets in my mill. I am just finishing a project where I hogged off a lot of 1018 with a 1/2" solid carbide end mill. Carbide mill are much harder to hold than HSS so I pulled the collet tighter but never had it slip.

 

[don-tucker]

We used to use screwed shank end mills in Clarkson collets at work,they screw up to a centre in the collet,they never move.With the event of CNC it was close fitting holders with the end mills held in with grub screws .
Don

 

[NickG]

Yes, I have used the screw clarkson type when Iwas at university, just a bit fiddley to change over but I can see why they were good.

Nick

 

[rake60]

I have used both end mill holders and ER collets to hold end mills.
I have never used an ER collet to hold an end mill larger than 1/2".
In the CNC department where I work, ER collets are preferred for
end mills under 1/2".

There are few rules of thumb.

The tool should be engaged by at least 2/3 of the gripping surface
of the collet.

The tool must never be bottomed out in the holder before the collet
nut is tightened.

The effective gripping size range of an ER collet is limited. Never force
a tool into a collet. The manufactures recommended size range is the
nominal size of the collet to -.039" There is one exception. In the ER11
series collets that rage is nominal to -.015"

End mills are very aggressive cutting tools.
If an end mill and spindle were one solid piece and it's pushed too hard
bad things would happen. If it didn't suck the spindle or head down, it
would pull the work piece up. Hogging or roughing with a standard end mill
will almost always create some kind of an issue. There are end mill designed
for hogging and roughing. They look exactly like this one.

Rick

 

[rake60]

It creates much more cutting surface in the contact area
reducing the tool pressure, allowing the tool to cut more
freely.

Rick

 

[hammers-n-nails]

so many replies. i have the split side type finger collets as nickg says. ive never used the endmill holders or the er's but have seen them never giving them much thought, which is prefered and why?. i dont know that the endmills are doing a great deal of spinning in the collet but i suppose they wouldnt have to spin much to slide out. rick i do have a few hog mills and the problem is much less with them, i like them alot but there so expensive, the one that i usually use i found in a dumpster with one corner broke off real bad so i cut the end off and it works perfectly well for side milling, about a $60 cutter i think.

this is a stupid question but is there really a rule on how much you should take off with each pass, with a 3/4" endmill i usually take about .100-.125 at a time sometimes more, with a 3/4" hog mill its not uncommon for me to go 1/4", at id say 4-5in/minute mabey, 4 and 6 flutes.do you think this is too much?

 

[Kermit]

Rick, I wanted an end mill for roughing aluminum, and had some other things I needed from Mcmaster, so, I looked up the number for one with a 3/8 shank and had them put it in the order. Seemed a very reasonable price for what I got.

It was just like the one you have pictured above. From NIAGRA cutters the label said.

So far I've only used it test milling small pieces on my lathe milling attachment. I have even knocked my lathe attachment and work piece(aluminum bronze) about a half inch out of position when I fed in to big a bite for my set-up. ;D

No appearant damage done to the end mill, as subsequent use will attest. meaning I finished roughing the piece of AlumBronze. after I changed my pants. Totally caused by operator in this case. pass after pass. back and forth. back and forth. The newbie in me said, go ahead, take a bigger chunk off next pass. Success led to further small increases in depth of cut and speed of feed. :-\

On the bright side. NOW I know how hard I can push it before I make a mess!


:big:

I have a total of 30 minutes experience in milling as of this writing so I'm literally contributing everything I know on the subject

Kermit

 

[Stan]

Home shops use the same size of endmills as pro shops but the load put on the mill cutter with a 1/2 HP motor is negligible compared to the same cutter in a 15 HP machine being pushed for max production.

 

[hammers-n-nails]

kermit thos niagra cutters are amongst the best as far as i can tell. im dealing with a 5hp machine so a 3/4" endmill isnt slowing it down too much. i said 4-5 in/min but i dont think thats right i think its more like 8-10 but thats a wild guess.