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Acetal nuts

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  • Greg Schley
    I just posted several pictures in the Photos section under Acetal Nuts.  These are of the Acetal nuts I made for my 33686 Mill Drill.  Wanted to get as
    Message 1 of 2 , Mar 21, 2013
      I just posted several pictures in the Photos section under Acetal Nuts.  These are of the Acetal nuts I made for my 33686 Mill Drill.  Wanted to get as little backlash as possible, but was balking at the cost of new ballscrews and ballnuts from China.  I came across this thread for making acetal nuts. I'm cheap so wanted to give it a try.

      I bought a 12" piece of 1.5" acetal off flebay for ~$15 shipped.  I did change the way he did it slightly.  The first one I tried really deformed in the vise.  So I put a piece of bicycle inner tube around the acetal pieces.  This put tension on the acetal against the leadscrew, and kept the shape really well.  I did use some channel lock pliers to compress it once up to temperature.  Also I used 2 heatguns so I didn't have to keep moving back and forth between sides.  Heated up to temp lots faster and more evenly I believe.  

      Briefly: Cut acetal to length on bandsaw.  Chuck in lathe and use an wood flat blade drill bit to bore a hole in the acetal.  This worked much better and faster than stepping it up with drill bits.  Used a boring bar to get it to the proper size: diameter minus thread on one side.  Cut acetal in half lengthwise on bandsaw.  Put rubber inner tube around it.  Slide acetal onto leadscrew, it has a 1/8" gap at the sawcut on each side, the tube holds it in place and tight.  I put it about 2"-4" from the end of the threads on the leadscrew.  Using heat guns I heated the leadscrew on both sides of the acetal.  You want the leadscrew to get hot, than that melts the acetal and forms the threads.  When it gets hot enough it doesn't take much pressure at all to compress it into the threads.  The rubber tube did most of it.  The acetal will squeeze out on the ends and also through the saw cuts.  Once cool it is a solid chunk on the leadscrew.  I let it sit for a couple hours to cool.  
      Now chuck leadscrew in lathe and true up the acetal.  I have a 7x10 and this was a real challenge to fit it in the chuck, and get it running pretty true.  I supported the other end of the leadscrew with a wire through the bearing block, hung at the right height.  Well it worked at least.  Just true it up, don't size it yet, as the surface will get chewed up a little breaking it loose from the leadscrew threads.  Now clamp the leadscrew in vise, protected of course and then I used a pipe wrench to break the acetal loose.  It was really tight.  I used a dremel to cuts 4 notches in the end of the leadscrew threads (just 3 threads deep) to act as a tap of sorts.  I turned the nut back and forth over that, cleaning out the notches each pass.  I ran it the length of the leadscrew, end to end a couple of times.  Once loosened up enough to turn by hand with some effort, I took the nut to the lathe to turn it down to size.
      I don't really have a way to make blocks to hold the new acetal nuts so I ended up boring out the original brass nuts.  Again, just chucked the brass nuts in the lathe and boring bar to cut them out.  The original holes were not centered, but I was able to fit each of the brass nuts in the lathe chuck and bore them out centered on the nut.  Once I had the brass nuts ready I turned down the acetal nuts to tightly fit.  I chucked each acetal nut  in the lathe and trued them again.  Next I turned a shoulder and then the rest to be a tight press fit into the brass.  I used a vise to press them into place.  

      OK.  My mill drill is still in pieces so I can't try it all out yet.  I am confident that they are going to work, but am contemplating a couple of small screws through the shoulder of the acetal into the brass to make sure they don't turn or get pulled out.  This was FAR cheaper than purchasing ballscrews and I kind of enjoyed making them.  I like that the stock leadscrews are much bigger than the ballscrews I would have purchased.  How it will play out over time remains to be seen.  My plan is also to convert it to CNC.  At least this way I should have a mill to make the motor plates with!  

    • Mar
      Here s another good thread on them: http://www.hobby-machinist.com/showthread.php/11166-Replacing-the-lead-screw-and-nut-on-a-mill?highlight=lead+screw+replace
      Message 2 of 2 , Mar 27, 2013
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