Drawbar for PM knee mill

[B2]

Your quill needs to be all the way up to access the drawbar, it moves up and down with the quill. Also holds true for a power drawbar, I bring the quill all the way up and lock it when using the power drawbar, otherwise the quill will move down and be disengage.

Some drawbars may be threaded too long and the R8 chuck/arbor not threaded deep enough, had that happen and destroyed the guide pin and an arbor. Got rid of the guide pin, ASAP. Checked all my arbors to see that they had a long enough threaded section.

Hi Mksj,

FYI: I too purchased the two the PM R8 "Ultra Precision Keyless Drill Chucks" that PM sells. One worked perfectly on the drawbar, but the other would not thread down into it as far. Matt and I both tried to run a tap down into the chuck without any luck. A lot of force was used. The threads went down into the chuck plenty deep. They are just too small in diameter. We think the Cr plating must have been ultra thick and filled up the threads. Anyway, that Cr is so hard that the tap would not touch it. End the end I just use a washer about 1/2 inch thick to go on the draw bar end against the spindle/spline. With the washer, the draw bar probably has a haft dozen threads into the chuck and this seems to be more than sufficient. However, it sort of defies the name "Ultra Precision...." , but the chuck works fine anyway.

I don't think the threading on the draw bar be too long.... you do not want to reach the end of the thread..... as long as it is threaded long enough to pull the chuck up tight.....that is all that matters. However, the length of the draw bar does matter and there appears to be some small variation, ~ 1cm, in the length of the draw bars for my 940M.

Dave

 

[benmychree]

It would be easy to slightly reduce the diameter of the threads on the drawbar, or make another one with smaller diameter threads, it probably would not take much to make it fit, in terms of pitch diameter. Another possibility is that the pitch of the threads may be a bit long or short, in that case a thread would start out fitting fine, and gradually get tighter; if the threads were cut with a die, this can happen easily, especially if cutting a non standard pitch diameter.