Printable View
Hi all been absent for a while and am now back to trying to finish off my CNC machine and was wondering does anyone know where I can purchase 3 X Delrin lead nuts for some Trapezoidal 12mm diameter leadscrews ? If you can make some or know any leads please post away or PM me many thanks.
Managed to buy some Delrin from E-Bay and was just wondering does anyone have a tap that I can borrow ? I'm sure I'll need a 12 X 3 trapezoidal one to get me going any helpers out there I would be greatly appreciative.
Hi, i will have a look because i used to sell these nuts on ebay. I dont think i've got a tap for Trapezoidal i think its just the ACME taps i had/used, will let you know shortly.
.Me
Hi,
No sorry its just the ACME taps i've got, a search on ebay give's a nice list of sellers from around the world, not sure how good they would be coming from China/Hong Kong but would get 3 nuts done im sure.
Failing buying one at those prices if some one or you have a spare length of Trapezoidal, you could make your own tap.
.Me
Hi Lee many thanks for looking. I can't remember but someone on this board had one and was going to let me borrow it and then I was to post it back but can't remember for the life of me who it was LOL! nevermind my search will continue.
I think it was me who offered to lend you the trapezoidal 12X3 tap.
PM me with your address and I'll post it to you,
Nathan
Nathan many thanks for the offer and will use it with care and post it back ASAP and I'll send you a little something back as an appreciation for helping me out "CHEERS" I'll PM you my details and will notify you as soon as it arrives so you know its arrived ok.
Hi Kammo, I've tried to make my own tap out of a piece of 12x3 trapezoidal leadscrew (didn't really want to pay £40 plus for a tap for 3 nuts) but I think I've flattened the profile a bit when cutting a taper on it as it's very loose on the leadscrew.
Nathan, any chance for a remuneration I could borrow the tap after Kammo?
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.
Attachment 5281
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.
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 :smile:Quote:
Originally Posted by motoxy
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.
Michael
Smart idea :whistling:
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.)Quote:
Originally Posted by artmin
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.
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 :smile:
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 :smug: