Help - I broke my lathe!

I assume you have a lead screw and nut in the carriage. Sence the problem is not aparent away from the point of impact, that leads me to believe the gearing is OK. Same thing with the nut in the carriage. I'd look to bent/deformed area in the lead screw. Might be able to use an old fashion file to true it up again.
Just guessing, need to see it to know for sure.
Karl

It's not in the screw, based on that the screw/half nut isn't engaged when I turn the hand wheel. The roughness is spread over a hand breadth of travel. Rack maybe? If I'm lucky I suppose.

I'm guessing that you've already checked all surfaces on the ways for damage and roughness, then ruled that out.
Yes, it sounds more like swarf between the ways and saddle. Try flooding the ways with light machine oil, loosening the saddle gibs and running the carriage end to end. It can float out the debris. Otherwise, you might have to pull the carriage to clean out the swarf.

Just having the half-nuts disengaged doesn't guarantee it is not the leadscrew. Bend it just enough and it will bow to drag on one half of the open half-nuts, thread crest to thread crest. Certainly worth checking out.
Just one of many possibilities, of course.
Good Luck, DoN.

Yeah, I'm thinking of pulling off the carriage and doing a cleaning and ins pection on that end. I only got the 20 year old machine recently, so it wou ld be good to have a look in there anyway. There is play in the gibs.
I loosened the screws on the rack and re-tightened them. I saw no movement. Now the tight spot has disappeared, but the handwheel turns roughly all al ong the rack. Maybe I bent the gear shaft or the bearing behind the handwhe el. I might try replacing the gears and bearing, but a good cleaning and ad justment of the saddle seems like the next logical step.
"Just having the half-nuts disengaged doesn't guarantee it is not the leadscrew. Bend it just enough and it will bow to drag on one half of the open half-nuts, thread crest to thread crest. Certainly worth checking out." Don, I checked the leadscrew with a dial indicator. Luckily it's still perf ectly straight!

With them adjusted properly? Not good, indicates wear.
Time to pop that baby apart and look for scrape marks, bent items, dragging rollpins, chewed gears, bad thrust bearings, swarf, etc.
Have someone shove the carriage back and forth while your fingertips are on the leadscrew. (This type of thing is really hard to do by yourself. DAMHIKT) If you feel vibration, it's likely hitting.

I doubt the carriage was ever readjusted after leaving the factory. The guy from whom I got the machine (see, I'm making an effort mit mein Englisch!) used it for brake work on ancient cars and motorbikes. He says he never us ed the powerfeed at all. He was certainly no machine geek. I doubt he kept up on maintenance, but carriage travel was smooth before the accident. So y es, My first job will be popping the carriage and checking underneath. The ways have some dings, but nothing major, and I'm truly not worried about th e leadscrew. There is light between it and the halfnuts, rack, and gear all along the travel path. Thanks!

robobass fired this volley in news:4da7d3cb- snipped-for-privacy@googlegroups.com:
Was the carriage being driven by the leadscrew, or by the feed pinion when it crashed?
If it was the pinion, it may have bent the pinion shaft, which would account for the roughness... it would be and odd-feeling sort of cyclic interference, in that case.
Lloyd

Am Montag, 28. April 2014 12:51:57 UTC+2 schrieb Lloyd E. Sponenburgh: b- Lloyd, It's a simple machine: pg
There's no feed pinion, just the half nut which is used for both threading and power feed. The gear on the rack to the hand wheel is always engaged, b ut now that I think about it, neither of those should have been affected by the accident, since they wouldn't have been under any drive force at the t ime. All this points to the saddle, or am I missing something?

Please restate the original problem. There appear to be various subthreads and answers may be confused.

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That is the pinion in question.
There *is* a feed pinion. It is geared (or directly connected to) the handwheel, and it would have been engaged full time -- as the handwheel turns when the carriage moves.
And a crash which tries to lift the carriage above the bed would attempt to bend the pinion, so that could be the problem.
Good Luck, DoN.

Ah! Wisdom from the masters!
Yes, that sounds spot on. Thanks!