More drawbar & milling cutter holder ??s...

[56type]

OK, I got the spacer made for the drawbar so I could use milling cutter holder. Final dimensions on the Spacer were 1.194 in. overall length, stepped down to 0.530 in. for a length of 0.187 of the overall length, with an OD of 0.750 in. over the remaining 1.007 in length. 0.375 hole drilled thru center for drawbar to pass thru. These measurements worked for the Atlas 10100 Mk.2 in case anyone might be looking for the spacer dimensions.

After getting the spacer made I set everything up...I noticed after tightening up the drawbar to the milling cutter holder that the cutter holder sticks out about 1.5 in from the end of the spindle, is this normal ?? The cutter holder has a set screw & the 0.500 in. hole, so I'm thinking maybe I'm missing some sleeves or perhaps another cutter holder for smaller mill cutters ?? The holder I have measures 0.710 in. at the big end of the taper & 0.590 in. at the small end, so MT2 ??

This was an ebay purchase that I picked up since the drawbar & milling attachment were in such good shape but it was missing the spacer & lower vise jaw. So I'm trying to figure out what else it may be missing ??...Thanks.

 

[wa5cab]

56type,

There are two ways to make the spacer. I'm not sure from your description which way you went. OD is the same. Most that you see are beveled on the right end and when nearly tight work OK. But I have found in practice that a slightly longer spacer with the right end turned down to just under the ID of the spindle works better. If you slide the reduced diameter into the spindle, and start the right end of the draw bar into the collet or cutter holder, the spacer will remain centered in the spindle while you are spinning it to run the threads in whereas with the beveled one you have to hold the draw bar hand wheel up to keep it centered in the spindle bore and not at an angle to the threads in the collet. It;s probably more noticeable on a 10" or 12" than on a 6".

On the cutter holder, Atlas sold a 2MT for the 6" and a 3MT for the 9", 10" and 12". The big ends are the same, with a set screw and an 0.500 (plus a couple of thou) to fit cutters with 1/2" shanks. The full kit also came with four reducing bushings, with a nominal 1/2" OD and an ID of 7/16", 3/8", 5/16" and 1/4". One of the variations to how end mills are made is the shank diameter. Some are made with the shank the same diameter is the cutter. Others are made with shanks in 1/16" increments. The reducing bushings were rather expensive to make I guess but with the factory cutter holder, you need them.

Another variation in the way that cutters are made is that some have a concentric shank. And some have a flat ground on the side for a set screw. This latter type are usually known as Weldon style, for the company that first made them. One thing that you do NOT want to make the mistake of doing is to use a Weldon cutter in a reducing bushing with the ground flat in line with the set screw. Once you have done that, you have a very expensive end mill because the set screw will deform the bushing down into the flat area and out against the sides of the 1/2" hole in the holder and you will not be able to get the end mill out.

 

[56type]

Actually I used the description of a spacer you provided in another thread on the subject...Here's a pic.

Is it feasible to hold milling cutters in the ER-25 collet sets as sold by littlemachineshop.com ?? Thanks.

 

[wa5cab]

Yes. So long as the nominal shank diameter of the cutter falls within the marked range of the collet. ER collet sets from some if not most vendors can be for continuous coverage or just to cover 1/16" increments. The latter sets are mostly for use in mills.