1/2" end mill pulling out of collet

Jake2465

Jake2465

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I was running a test program yesterday night and about 20 minutes into it I noticed that my Z heights started acting strange; the end mill was digging deeper than it was supposed to. At first I thought perhaps the encoder on the Z had some problem, but then I noticed that the end mill looked a lot longer than I remember it being. I pulled that tool holder out and checked the tightness of the collet nut. It was tight, but not ridiculously tight. So, I just cranked on the wrench a little more. Is there an actual foot poundage that should be used for ensuring the end mills don't slip out of the collet besides using the German "goot-n'tite" method?

I run with the DA180 collets and the NMTB30 tool holders.
 
Jake2465 said:
I was running a test program yesterday night and about 20 minutes into it I noticed that my Z heights started acting strange; the end mill was digging deeper than it was supposed to. At first I thought perhaps the encoder on the Z had some problem, but then I noticed that the end mill looked a lot longer than I remember it being. I pulled that tool holder out and checked the tightness of the collet nut. It was tight, but not ridiculously tight. So, I just cranked on the wrench a little more. Is there an actual foot poundage that should be used for ensuring the end mills don't slip out of the collet besides using the German "goot-n'tite" method?

I run with the DA180 collets and the NMTB30 tool holders.
Click to expand...

I use the Tormach TTS system which uses a 3/4" R8 collet with ER20 tool holder. I have had pullout occur when side milling. Usually it is associated with heavy cuts. A high helix end mill is more prone to pullout. Conventional milling is more prone to pullout than climb milling. Pullout issues are usually solved by re-tightening the collet.

I don't torque my ER collets but it would be safe to say that I tighten the snot out of them. The final tightening usually involves arranging the wrenches in a pliers-like fashion and tightening one against the other. Based on the lever length , I would estimate something like 20 -25 lb.-ft. of torque

I don't have a power drawbar but I tighten the drawbar fairly tight with a 6" wrench, probably something like 30-40 lb.-ft. of torque.

Looking at the DA180 collets, they have a much faster taper than the ER collets which means a lower mechanical advantage. This in turn means more torque has to be used to get the same holding power. Another factor can be increased friction in the threads of the collet chuck. A light lube on the threads will increase the torque used to tighten the collet.
 
I have wondered about that myself . I had a roughing end mill do that but pretty much chalked it up to a dull cutter.I have also heard that climb milling will tend to do it. An end mill holder may be the best way to go. I guess I was wrong it must be conventional milling rather than climb.
 
Ugh, that's unfortunate for me. For now I will just have to work with what I've got as all of my tool holders are collet type. I will just have to crank on them really good until I can afford to go with something more suitable. I have not purchased any of those weldon style tool holders for two reasons: the length of the end mills cannot really be adjusted and the end mills need to have flats ground in the sides. So making the switch to that style of tool holder will probably drive the cost of the end mills up.
 
I'm slowly buildilng a set of Weldon holders for my PM25. I've got 1/8 and 3/8 so far, hope to get 1/4 soon and then duplicates. It's a lot easier to put a holder in the snout than a collet and tool.
 
Jake2465 said:
Ugh, that's unfortunate for me. For now I will just have to work with what I've got as all of my tool holders are collet type. I will just have to crank on them really good until I can afford to go with something more suitable. I have not purchased any of those weldon style tool holders for two reasons: the length of the end mills cannot really be adjusted and the end mills need to have flats ground in the sides. So making the switch to that style of tool holder will probably drive the cost of the end mills up.
Click to expand...

I've not had that problem, but I tend to be a bit heavy handed in tightening the DA collets, using a 12 inch crescent wrench and pull on it until it stops turning. :) Most endmills by default have Weldon shanks, only some of the smaller single end carbide don't, most of the smaller double end carbide do. For heavy cutting, I use tool holders.
 
JimDawson said:
I've not had that problem, but I tend to be a bit heavy handed in tightening the DA collets, using a 12 inch crescent wrench and pull on it until it stops turning. :) Most endmills by default have Weldon shanks, only some of the smaller single end carbide don't, most of the smaller double end carbide do. For heavy cutting, I use tool holders.
Click to expand...

I am about to buy a 1.5" crows foot so I can put my click style torque wrench on there... Funny that it lasted for 20min before starting to pull out of the holder.
 
[QUOTE="JimDawson, post: 612356, member: 29628"... I tend to be a bit heavy handed in tightening the DA collets, using a 12 inch crescent wrench and pull on it until it stops turning. :) Most endmills by default have Weldon shanks, only some of the smaller single end carbide don't...[/QUOTE]

I had a similar problem with a single end carbide mill, which was in a router (and used on wood). A router chuck doesn't
have the right construction to use a heavy wrench, but it was possible to roughen the shank by dipping it in boiling hot
chlorine bleach. Once the mirror finish was dulled, the collet held it much better.

The ultimate solution, would be to shrink a collet-shaped collar onto the shank; the collet chuck would hold that quite securely.
 
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