Overcoming backlash

Hi everyone. I have an old Colchester Chipmaster which was exhibiting, (what I considered), excessive amounts of backlash in the table slide and cross slide lead screws, (please excuse me if my terminology is incorrect!). Anyway, I have seen various remedies to curing this, (other than replacing the lead screws and nuts), and I'm sure there are already numerous threads on this forum addressing this but here is the solution I came up with which seems to have fixed the problem.

First off, with the lead screws and nuts removed, I refitted the tables and adjusted the gibs, (?), to eliminate any movement in that area. My next step was to figure out a way of adding some controllable adjustment to the screw/nut. The method I came up with worked well on my model of lathe but I don't know how successful it would be on others as I have very little familiarity with other makes and models.

I drilled through the centres of the retainers for the brass lead screw nuts and tapped them out, (6mm worked fine for mine). This was to accommodate a 6mm grub screw with a spring loaded ball end.

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I then melted the end of a plastic coat hanger and forced this in to the thread for the retaining bolt in the brass nut, with the nut in position on the lead screw where the most play was apparent. Once set I trimmed the hardened plastic and heated up a screwdriver blade to put a slot in the plastic. The plastic plug could now be screwed out giving you a plug with a thread on the end that matches the lead screw.

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I then cleaned the threads off the outside of the black plastic plug so it floats in the threaded brass nut rather than having to be screwed in to it. With the nut on the lead screw in its position with most play, the plug is dropped through the brass nut thread ensuring that it sits in the thread on the lead screw. The grub screw is then screwed in until it lightly loads up on the plastic plug, (note, I had to play around with the height of the plug, trimming it down a few millimetres at a time until I got it to a height where the grub screw had enough travel on it without interfering by sticking out of the top of the brass nut).

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With the grub screw loaded up lightly against the plug at the position on the lead screw where the most play is, this eliminates the backlash at that point. As the handle is turned and the brass nut works its way to either end of the lead screw, where there was little or no free play, the plug pushes back against the ball in the spring loaded grub screw and in doing so, doesn't tighten up the operation of the lead screw.

It worked for me! Hopefully it will help out others in a similar situation.

Guy