Drag after nut replacement

[wawoodman]

I just replaced the cross-slide and compound nuts on my 1978 10K. There is a LOT of drag (tight, loose, tight, loose) as I rotate the handles. I've tried loosening the nut retaining screws, and the gibs are properly adjusted. The only thing I can think of is that the screws are bent, and it wasn't a problem before, because the nuts were worn, as well.

Any other suggestions, before I pull it all apart, again?

Thanks,
Mike

 

[Tony Wells]

I'd say the screws are bent, and that will wear the new nuts out. Probably why it was free before was the wear on the nuts. Lots of times the handwheels get smacked and the bend is on the step down. Can you see any "wobble" in the dial face, or variation in the gap where the grad wheel mates with the index plate?

 

[wawoodman]

Dave, the screws look good. The acme is still nice and crisp.

Tony, no wobble or variation that I can see, but I'll look again.

Thanks, guys.

 

[Tony Wells]

Mike, I'd be concerned about bends near where the screw is necked down to fit a bushing or where a handwheel fits. Sharp corners bend much easier than radiused corners. Lots of people seem to prefer cutting a sharp corner over an edge break on a bore where they must fit together. This makes a weak spot. You could probably check for runout by removing the handwheel, and putting an indicator on the extreme end of the shaft/screw. If you can still turn it, it should show up there if it is bent. Otherwise, you'll need to disassemble it again. Sorry about that. Might have been wise to check for bent when you had it scattered before.

 

[wawoodman]

Thanks, all.
Upon further examination (now that I know better what to look for) it appears that you guys are right, and that the screws are bent. On the compound, it's a very slight wiggle, but it's definitely there. On the cross-slide, it wanders all over the place. So it looks like new screws are in my future. (I assume these would both be dead nuts straight, right?)

Dang.

Of course, I've always said that there are very few problems that you can't solve, by throwing money at them!

 

[Tony Wells]

Mike, this is a good time to bring out the inspector inside you. If you have vee blocks, start by mapping out the bend. You need to know as closely as you can where the apex of the bend is. I use a sharpie to mark the high spots as I rotate them on the vee blocks, and note the amount of runout at each point. I space the test points about .500 apart to begin with, and when i get close to knowing where the center of the bend it, I close that up to about 1/4". Once you find out where the apex of the bend is, then Jim has given a good method to straighten the screws. I would wager that you will find the bend on an inside corner, as I mentioned above. It usually doesn't take a huge force to bend (or straighten) feed screws.

If you don't have vee blocks (yet ) use your latheas a set of bench centers, and do the inspection.