Repair of Leadscrews and Nuts

Repair of Leadscrews and Nuts

Repair of Leadscrews and Nuts - The purpose of leadscrew is to permit a fixed movement of the lathe saddle/carriage in relation to one turn of the lathe spindle; that is, to allow the cutting of threads on the workpiece.

Most machine tools have square or acme screws and nuts for actuating tables and slides. The rate at which they wear and need attention will depend on the amount of use they receive; the cross-slide of a lathe and table screw of a milling machine being two examples which are most used on those particular machines.

The bronze nut, being softer than the steel screw, wears the more rapidly, and eventually has to be replaced. The screw, however, becomes subjected to wear and, as in the case of a cross slide, most of the use takes place from the point where the tool is at the centre, to a point a few inches out, the screw becomes most worn in this region.

Wear of Threads on Cross Slide Screw

This wear results mainly in a thinning of the threads, and when it has become appreciable a nut screwed to suit the unworn portion of the thread will still give rise to backlash when in mesh with the worn part of the screw.

Since the nut must be made to the unworn end of the screw for the purpose of assembly, the remedy is to set up the screw in a lathe and pick up the thread wi th the correct change wheels. By working to the profile of the worn portion the rest of the length may be cut to match, giving a uniform if thin thread for the whole length of the screw. The new nut may then be cut to suit and the combination will operate without backlash over the whole travel.