If you ever use trapezoidal ACME thread Im told that a good low backlash nut can be made from that low melt point plastic called polycaprolactone (or PolyMorph, Shapelok, etc).
The way its done is to make a piece of it around the right size with a rough hole just larger than your ACME.
You then heat the ACME with boiling water etc then clamp the plastic onto the thread. The thread heats the plastic to the point where it will mould itself around the thread.
When its set or just about set you unscrew the ACME, job done.
Apparently it takes a few goes to get it exactly right but then its easy.
I've not tried it yet but I just ordered some polycaprolactone granules, 100g for £1.25ish.
Very handy stuff for other things too Im told. Provided its not paper thin its very tough stuff, have a Google for some of the interesting uses people have found for it.
When mine arrives I'll start a thread with photos and see what sort of results I get.