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Thread: Making Acetal leadscrew nuts the easy way

  1. #291
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    To summarize the thread.

    You get a rod of delrin/acetal.
    Drill a hole through it slightly smaller than your leadscrew
    Cut it in half, length wise.
    Take the two halfs and clamp/squeeze it around the leadscrew
    Heat the leadscrew until the two halfs melt around the leadscrew (heat gun takes too long, use a torch)
    The new nut will feel like its glued to the leadscrew, unturnable. While your thinking what to do
    throw the leadscrew and stuck nut in your's or a friends lathe and clean it up on the outside.
    While you have the leadscrew secured, grab a big ass channel lock and make that nut move.
    Keep working it.
    Find an area of the leadscrew that is never used (or a junk piece of leadscrew) and cut a section of thread
    away effectively making it a cutter. and just run the nut back and forth over this cutter section until your
    satisfied with the movement.

    Thats about it.

    Heres a pic of my worn out brass nut on the left and my delrin project on the right



    And here is a pic of the finished nut.



    Ohh .. and a just a quick pic of what I mean about cutting a little unused thread away for cutter

    Last edited by Mike Amick; 01-27-2019 at 03:08 PM.
    John Titor, when are you.

  2. #292
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    I did that too- in my case I just cut a slot across a few threads rather than making the divot like that last pic shows. There was enough of a burr left that it would cut and after a while the nut could be turned much more easily. It certainly was stiff at the start, requiring some wrenching to get it to move at all.

    But I don't like the idea of having to machine the as-formed surface to make it turn easily. I tried a two-part casting, which basically meant laying the threaded rod halfway into a channel of epoxy. After making two of these, I cleaned them up and surrounded the threaded shaft with the two separate parts. For one of my projects, I filled the gap on both sides between the parts with epoxy, figuring that now only a small section of the epoxy would be gluing itself to the shaft, and could be loosened up easily. This was better, but it was still tight. After that I figured that a three piece mold would be ideal- it all gets set inside a metal holder anyway, and the tightness of the fit directly translates into the tightness of the final nut on the shaft. There is no need to alter the as-formed threads in the plastic at all, which leaves the best area of contact between the threads in the nut and the threaded shaft. By the way, I did coat the threaded rod with a non-stick coating before doing any of the casting. I used Top Kote, which is meant for table saw tables to lower the sliding friction. I sprayed one coat, polished it, then sprayed a second coat and didn't touch it after that. I figured that some of the teflon would embed in the surface of the casting and help to make it friction-free. Seems to work ok.

    If I was re-doing this today, I'd be using this last method- either casting an epoxy in a 120 degree wedge shape or heat-forming the UHMW or whatever into that shape. This is much easier to break free from the lead screw threads than even the 180 degree shape. Surround the lead screw with three of these, then temporarily wire them in place so you can turn the od for a nice fit into the holder. Using this method you can set the tightness of the fit around the lead screw without having to alter the formed surfaces of the threads at all.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  3. #293
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    Quote Originally Posted by darryl View Post
    I did that too- in my case I just cut a slot across a few threads rather than making the divot like that last pic shows. There was enough of a burr left that it would cut and after a while the nut could be turned much more easily. It certainly was stiff at the start, requiring some wrenching to get it to move at all.

    But I don't like the idea of having to machine the as-formed surface to make it turn easily. I tried a two-part casting, which basically meant laying the threaded rod halfway into a channel of epoxy. After making two of these, I cleaned them up and surrounded the threaded shaft with the two separate parts. For one of my projects, I filled the gap on both sides between the parts with epoxy, figuring that now only a small section of the epoxy would be gluing itself to the shaft, and could be loosened up easily. This was better, but it was still tight. After that I figured that a three piece mold would be ideal- it all gets set inside a metal holder anyway, and the tightness of the fit directly translates into the tightness of the final nut on the shaft. There is no need to alter the as-formed threads in the plastic at all, which leaves the best area of contact between the threads in the nut and the threaded shaft. By the way, I did coat the threaded rod with a non-stick coating before doing any of the casting. I used Top Kote, which is meant for table saw tables to lower the sliding friction. I sprayed one coat, polished it, then sprayed a second coat and didn't touch it after that. I figured that some of the teflon would embed in the surface of the casting and help to make it friction-free. Seems to work ok.

    If I was re-doing this today, I'd be using this last method- either casting an epoxy in a 120 degree wedge shape or heat-forming the UHMW or whatever into that shape. This is much easier to break free from the lead screw threads than even the 180 degree shape. Surround the lead screw with three of these, then temporarily wire them in place so you can turn the od for a nice fit into the holder. Using this method you can set the tightness of the fit around the lead screw without having to alter the formed surfaces of the threads at all.
    Did you make an EvaNut or a cast epoxy nut?

  4. #294
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    I thought Evan came back to visit when I saw this post. I wonder if anyone makes an Acme thread mill? That by far would be the easiest if you have CNC, would allow you to dial in the thread class as tight as you want. Could do it with a hand ground form mill, just set it up in Fusion360. Easy peasy.

  5. #295
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    My latest projects have been cast epoxy. Previous to that I did experiment with uhmw, but I did not melt the plastic enough for them to weld together as Evan did. One thing I did do was to start with uhmw flat bar, laying the lead screw across it and heating the screw until it wanted to sink into the plastic. At that point I applied pressure and waited for it to cool. I made two pieces like this, then sandwiched them around the lead screw. After squaring it up and trimming to size, I pushed the assembly into a piece of square aluminum tubing, which becomes the nut holder. I didn't get a full 360 degrees of threads this way, but it did work very smoothly with no detectable play.

    Another idea I started with but never carried through- drill and tap the plastic nut material, then screw it onto a piece of lead screw- but then heat the screw as with the Evanut and hopefully melt the plastic against the threads. No pressure involved, hopefully the plastic will flow and relax into the threads, repairing the damage done by the tap. With luck this might result in a close fit and a high area of contact without too much friction.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  6. #296
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    I am almost ready to form my nut in acetal but still not sure about the kerf on my cross slide screw.
    Want to post pic. but it challenged. I see the kerf filling and it will be impossible to turn off without twisting the lead screw.
    I try again to post pic, url ??
    Last edited by Lee56; 01-28-2019 at 03:18 PM.

  7. #297

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    Mike Amick;

    That nut looks suspiciously like it is for a Millrite. Is it?

  8. #298
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    Quote Originally Posted by mikegt4 View Post
    Mike Amick;

    That nut looks suspiciously like it is for a Millrite. Is it?
    Your suspicions are correct
    John Titor, when are you.

  9. #299
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    Quote Originally Posted by RB211 View Post
    I thought Evan came back to visit when I saw this post. I wonder if anyone makes an Acme thread mill? That by far would be the easiest if you have CNC, would allow you to dial in the thread class as tight as you want. Could do it with a hand ground form mill, just set it up in Fusion360. Easy peasy.
    I have a CNC lathe. Could that cut it or does it have to be live tooling? JR
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

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