[rsfairman]

I've been going over a milling machine I acquired recently, fixing various things, and the x-axis ball screw is a little out of place. The machine is from around 1991, and the most similar model I can find on the internet is the YCM40 Supermax.

Here's a picture of the outboard end of the ballscrew.

Attachment 267656

The end of the ballscrew doesn't stick out quite far enough to get a circlip on there. I know that it should have one because, when I removed the cover, there was one in there, and it had gotten bent as the screw moved and the circlip was forced off.

Here's a picture of the motor-end of the ballscrew.

Attachment 267658

The ballscrew needs to move through this housing by maybe 1/16 so that I can get the circlip back on. I tried loosening the collar in the center -- I mean the one between the pulley and the black ring -- by loosening two set screws and tapping on the keyway-looking groove, but no dice. I can see that someone really whaled on this at some point. One of the keyway looking things has a deep groove like someone pounded tangentially with a hammer. I tried pounding in the opposite direction, but it wouldn't go, but I didn't want to pound on it very hard.

I would have a better idea what to do if I had some idea how this all went together. Anyone been down this road?

Thanks,

Randall

[underthetire]

Pulley looks to be a collet type, get that off first. Don't just loosen the set screws on the collar, remove them. I've seen double set screws on some collars. Once done with that, a cold chisel and heavy hammer and shock the collar loose. Once that's off, remove the cap screws on the pre load collar and remove. Bearings should now come out of the housing with the screw by pushing on the table, or rotating the screw by hand. Just loosening the collar to push the screw back for the snap ring is a bad idea, you will loose all the pre load on the thrust bearings and create gobbs of backlash. I wouldn't worry too much about the snap ring, that end of the support does nothing on that machine other than keeping the end of the screw from whipping.

[rsfairman]

I've have things apart, and I'm not sure whether I'll try to fix this problem or not.

The pulley is held in place with a series of overlapping wedge-shaped rings The screws in the outermost plate put pressure on these wedges to get a tight friction fit.

The collar on the inboard side of the pulley screws onto threads on the shaft of the ballscrew. There's a shoulder on one side of the ballscrew that butts up against a thrustbearing, and this collar acts as the other shoulder once it's been screwed on. To fix the problem what I would need to do is put some kind of spacer on the inboard side of the thrust bearing. Then the screw would extend by the thickness of this spacer further into the other end. As you say, the purpose of the bearing at the other end is to keep the screw from whipping. In theory this bearing could migrate off the end of the screw without a clip, but it hasn't happened yet, so I lean toward leaving well enough alone.