Delrin Lead nuts.

[artmin]

I know this is a resurrection of an old thread but it may be of use again.

The Z axis on my router has a trapezoidal thread with a delrin nut which managed to gain about 0.1mm backlash. I was finding it difficult to source the right flange nut to suit so I broke out the 'polymorph' (you can get it on ebay). Polymorph is a low melting point mouldable plastic. Here's a picture of the new polymorph nut.



I cast it in situ in the machine by clamping the z axis in position and then used the old nut screwed up form below to centralise the screw. Then using a blow torch, heated the machine frame & screw lightly to about 60degC (I did remove the limit switches first). I then spent about 5 mins kneading the polymorph down into the recess around the screw. Once I was happy I couldn't get anymore down I left it to cool. On cooling it does shrink back slightly so the new nut comes out of the aluminium housing quite easily & is quite tight on the shaft. I could screw it off though. Next step was using a craft knife, to slit the new nut. Then I inserted a slip of plastic into the cut to spread the nut and to make it a press fit into the aluminium housing. This made the nut quite a good fit to the screw, but I honed the two together using T-cut of all things. My Z axis has about 75mm of thread at the end which is never used so I used that part to hone. Once I had the perfect fit, I dropped the screw & nut into the ultrasonic tank to remove the cutting compound, oiled & rebuilt the machine. The results have been perfect but I will have to wait (hopefully much) longer to see how it wears over time. But certainly there is no backlash & the recess in the aluminium housing due to the shorter nut maintains a resevoir of thin oil.