What could cause a cross slide screw to bend?

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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