Acetal / Delrin cross slide lead screw nut.

[Dranreb]

Keep us updated if this works there maybe other use's for this. Thanks Ray

Well it's been a while and I've given it a fair pounding in that time.

After a bit, seemed that a little wear was taking place, but on inspection it appeared to me that the Acetal was changing shape, as the slot was wider than it had been.

I tightened the screws which achieved zero backlash again, but today I noticed that some backlash has re-appeared...

I think I have kept chips out of it, but some of them pesky things may have sneaked in somehow,

Re tightening the screws until the gap was closed reduced the backlash, but not entirely, so sadly I have to own up and declare this particular design a failure as a long term fix..

I think it must be my way of making a pastic nut, as I haven't read of any other designs failing.

Did anyone else try making one? If so how did yours last?

Bernard

 

[8ntsane]

Hi Bernard
I have read so many success storys with delrin nuts, I wonder what is different with yours.
Seems you did a good job making the nut. Maybe the problem is else where. I have read the original thread from Evan. He did say he spent some time prepping the screw to ensure the burs were removed, and he also polished the screw. I have to wonder if you did that, and maybe you need to do a very close inspection of your screw to see if it could be the problem. Also, did you run the screw and nut dry? or was a lube of some sort used? There was talk of using different things in the original thread. I don't know if it extended the life of the nut , or not. There was also talk of different types of delrin. Was the correct type used? Just wondering what went wrong. Could it be the materials, screw prep, lube, or no lube? Seems you did a fine job making the nut.
Hope you find out why your getting the wear. Let us know what you find.

 

[Dranreb]

Thanks for interest Paul, I think the plastic has to be enclosed in a metal housing somehow, as others have done, there may be some flexing going on, maybe the spigot has worn or is flexing a little as well, I'll have to check that.

It is known that these plastics can 'settle down' after machining, causing problems with achieving very accurate dimensions.

As the nut was not a full circle, and heat was used I think it has moved a bit like wood drying out. Milling with the cross slide gibs pretty snug may have put extra strain on the nut and forced it apart.

It was OK dry, but a little lube made it very smooth, I only lubed it once.

The difference having zero backlash made to the lathe was amazing, especially when milling, I've picked up a few quality NOS end and 2 flute cutters cheap and was able to mill better than I ever hoped with my little Atlas.

Hey ho...back to the thinking chair (I Don't have a drawing board)

Bernard

 

[iron man]

I dont think I would give up as of yet. I would try making a tap out of an old piece of acme threaded rod and tap it instead of heat forming it. I know that plastic when heated lose's its oils and will change shape and can get brittle over time. If that is not it maybe enclose it in a metal shell. Or maybe another plastic such as Turcite... Ray

 

[Dranreb]

No I haven't given up yet iroman, just giving it more thought, I do lean towards the impetuous sometimes...

Bernard

 

[8ntsane]

Looking at the pics again, I wonder if the screws that you say are self tapping are maybe the problem?
Meaning the plastic they thread into is being pulled out of shape some. Do you have room to change them
to a nut and bolt arrangement? , with possibly a nyloc nut? I was thinking there must be a fair bit of force
to close the gap when adjusting back lash. If you have room, it could provide a better clamping force. Just a thought.

You also mention lube helped. If I recall that thread Evan started, there was talk of coating the screw threads
with graphite, and I think other talked about wrapping the screw with Teflon tape befor the heating process.
I don't know who tried what, but the thought was to impregnate the delrin with what ever was used. That just come to mind when IronMan mentioned the material losing the oils from heating, and drying out some.