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rp designs
02-18-2011, 10:50 PM
So I bought some cheap inexpensive chinese ER-40 collets to cover the spectrum of holders I don't have many of for my NMTB-30 holders. However I have found that Under heavy axial loads i am getting a lot of movement of the end mill (it either will push into the collet or pull out) and I am tightening these things as tight as I possibly can. I have tried a couple different holders and the same thing happens. I am fine with the other holders for the bigger size mills, but when I get to 1/4" and below I simply don't have enough holders and it gets pricey to get the NMTB-30 stuff. Is there a better, cost effective system out there for the Home shop guy, that will resist axial loads better and not break the bank?

Black_Moons
02-18-2011, 11:21 PM
ER-40 specs 125ft-lbs of torque for full tightening.
http://www.spindletool.com/TECHNIKS/TECHNIKS-TORQUE-CHART.htm

Basicly meaning, you are most likey not tightening it nearly enough, You need to make some kinda holder for the ER chuck, then make a longer wrench, then crank it down as hard as you can.

You can't really do it mounted in the mill without snaping something.

I wonder if it would be worthwhile to grease/lube the collet nut threads? Likey prolong there life, and let you get it tighter per lb of torque.. But not sure how well greased threads hold up to vibration.

djc
02-19-2011, 02:30 AM
As the reply above says, you need to do them up _tight_. Another option is to buy a good quality ball bearing nut.

A further option, but one that does involve expense, is to buy a straight shank ER16 or 20 holder (CTC tools) and hold that in the ER40 chuck, and then the small tool in that.

Paul Alciatore
02-19-2011, 03:04 AM
For the best grip, collets should be carefully cleaned where they need to grip and lubricated where they need to slide when tightening. For the ERs, the lube should be on the OD ONLY and the ID should be completely dry.

macona
02-19-2011, 03:18 AM
There are some really cheap collets out there. See if the collet is cut correctly.

Also I make sure I am using imperial sized collets with imperial size cutters. Real cheap ones are almost always metric. Better ones will be specifically ground for inch tooling. With matching parts they will grip better and tighter.

SGW
02-19-2011, 06:02 AM
I think your problem may be "...cheap inexpensive chinese...."
Buy a good-quality 3/16" collet (I assume you use that size the most) and see if it works any better.

FOG
02-19-2011, 08:41 AM
I had this problem with my 10,000 rpm Kitamura CNC. The simple fix was to use very fine lapping compound on the mill shank. working a fine layer of this stuff on the fit into the collett gave the grip needed and did no damage.

FOG