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  1. #11
    Quote Originally Posted by motoxy View Post
    Now that's clever. I thought polymorph was an alien life form on red dwarf.:whistling:
    That's what most people think. I bet the plastic was named by a Red Dwarfie

  2. If anyone is still looking for delrin 12 x 3 single start nuts. I have 2 that are not of use to me. There are DumpsterCNC model TR12031-LN with the rounded edge two flange on them. If anyone is interested drop me a line.


  3. #13
    Smart idea :whistling:

    Quote Originally Posted by artmin View Post
    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.
    Plus when it does wear you can just remould it. (Edit: Clearly taking it too far but theoretically you could build in a coil inside the nut to surround the screw then pass high frequency AC through that to induction heat the screw every so often (not whilst running!) causing the nut to remould itself to remove any wear. Self healing nut.)

    I'd me more surprised if there was any backlash. Gravity causes there to be a constant force pushing down on the Z-axis nut, effectively pre-loading. So as long as the force due to static friction does not exceed the weight of the Z-axis and the component of cutting force parallel to Z-does not either you will not get any backlash. For this reason the backlash on my ball-screw driven Z-axis is smaller than I can measure. Most likely with the previous set-up the static friction was too great so the Z-axis didn't naturally 'fall' into position.

  4. #14
    Good thought on the heating whilst in location, but I found that with my Nema 23s, the resistance was too great once the polymorph cooled. I had to slit them to reduce the friction. It was an easy job, about an hour all in. I doubt it would be a problem for larger motors though.

    As for the backlash, the old nut was a rattley fit. Most of my work is cutting hard aluminium, clearing plateaus areas. What I noticed was as the cutter plunged in on Z, the head was being pushed up against the screw by the reaction to the plunge, and with no dwell time on Z down, the movement on X&Y was leaving a 0.1 ramp as the head slowly dropped down on the backlash whilst traversing. With the feedrate used the ramp was about 15mm long. It didn't look good after anodising.

    All sorted now though

  5. #15
    A wee update on the polymorph lead nut. Three years on and it is still in perfect condition and in daily use. No noticeable backlash at all (not measured, just feeling for it) and the aluminium machining shows it. Just a drop of oil daily

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