# What could cause a cross slide screw to bend?



## AndySomogyi (Nov 21, 2019)

I just spent the last few days straightening the taper attachment half of my cross slide screw (Clausing 5400), and rebuilt the taper attachment block with new bearings.

Now I find out that the other half is also extremely badly bent.

Originally the taper attachment side was bent about 25 thousands, got it down to about 1-2 thousands.

The front half screw is bent about 15 thousands.

I don’t understand how these could get bent so badly.

Someone was clearly in this lathe before as there are vise grip marks on the tail of the screw and were on the threaded section.

Could a screw get bent though normal use or wear? 
	

	
	
		
		

		
			






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## cathead (Nov 21, 2019)

Probably was bent with abnormal use...  Good job on straightening it to 1-2 thou.


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## pontiac428 (Nov 21, 2019)

Think the prior owner might have done a lot of heavy knurling with it?


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## DAT510 (Nov 21, 2019)

If you cross-slide has power feed, it could have been crashed while under power.  

When I got may lathe, the power cross feed didn't work.  When I dug into it, it appeared to have been crashed, as the taper pin for the drive gear had been sheared.


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## Ulma Doctor (Nov 21, 2019)

+1 on CRASH, bad crash


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## MontanaLon (Nov 22, 2019)

Only if normal use includes crashing, likely more than once and probably at high speed.


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## C-Bag (Nov 22, 2019)

Not exactly the same but a demonstration of what can happen. Lead screws by their very construction are weaker than a plain rod in my mind. My old shaper had two lead screw mechanisms that were totally stuck. One was the tool head and it turned out somebody had tightened down one of the gib screws tight enough, along with a lack of oil, to gall the gib and pile up some of the gib material. Both gib and lead screw were bent which I would have thought impossible being the handle being tiny/short and the lead screw being only like 5" long. Somebody really CRANKED on it and something has to give.

The other was the short crank gear screw that adjusts the length of cut. It's very short but the nut slides along the mechanism and all the other parts that interact with it need to be loose to be able to adjust it properly and because it's adjusted with the universal crank that offers a lot of leverage. The nut coupling is offset so somebody decided to crank on it when the rest of the mechanism wasn't loose. Bent it enough where it wouldn't travel it's whole adjustment and totally bind offering only 1/3" of its adjustment.

I was able to use my arbor press with feeler gauges to micro straighten both back to work smoothly again. Something I'd never tried before but through desperation worked. I can only imagine the longer the leadscrew the easier to bend.


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## cjtoombs (Nov 22, 2019)

+1 on the crash theory.  The handle end might have been hit by something or the lathe dropped at some point before you acquired it.


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## Cadillac (Nov 22, 2019)

First thing that would come to mind is she fell over. How are all the handles? Check backside of taper attachment for marks. A crash on the cross slide maybe but hard to see??


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## GL (Nov 22, 2019)

+1 for it got tipped over.  Kills me to admit it, but I tipped mine over trying to level some adjusting screws.  Bent the cross slide screw, broke handles...idiot move, learning experience of highest dumb level.  Why yes, they do have a high center of gravity, even if they are "small".   New parts, patience, and cursing will get it back.  Probably never sell it because of that incident.


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## Sblack (Dec 10, 2019)

anything that tries to turn the lead screw when the slide can't move (because the gibs are too tight, or the slide has hit something solid, or somebody has reefed it to deepen a knurling cut or the machine has fallen over - take your pick. An overwhelming force met an immovable object. In the end it doesn't really matter what did it. I would check for collateral damage on the nut or the nut mounting. Every part in the chain is going to be stressed to the max and usually the nuts are softer material. I know my nuts are made of a soft material! But the good news is that a reasonably skilled hobby machinist can make all this stuff. None of it is rocket science. You can buy acme threading inserts which makes turning those screws even easier if you are lazy, or make your own. You can buy acme taps from China for a reasonable price. I had good luck single point treading with a conventional 60 deg thread first to remove material, then ran a tap through when I built new half nuts for my logan. I had no idea what I was doing but it turned out very well - flanged bronze inserts silver soldered in place on the cast iron nuts that had been bored out. But yes, it is a bit discouraging when you find a nice machine has been horribly abused. Makes you feel better when you set it right. I also made new graduated dials and installed thrust bearings which really improved the feel of the slides. I borrowed the design from the George H Thomas book from Tee Publishing. I had a great time rebuilding that lathe and learned a lot.


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