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Making Acetal leadscrew nuts the easy way

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  • Wow, as Evan stated its pretty easy to make these nuts.

    To get familiar with the process I made a "test nut" for a piece of 5/16"-18 threaded rod.

    I was concerned that if the heating wasn't done very carefully that at some point the acetal would get too blobby and melt away from where I wanted it to stay but that didn't happen. It got soft and deformable but not blobby.

    I just used light spindle oil on the threads for this test but if anyone has come across a better type lube or compound to put on the threads prior to heating please chime in.

    I used a heat gun but the real screw will be 5/8"-18 and I don't think the heat gun will cut it on this big screw so I'll use a propane torch for that.

    Paul T.
    www.power-t.com

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    • Excellent thread Evan, thank you for taking the time to describe your method. I plan on trying it out this weekend for a Colchester Student cross slide nut. I was quoted over $640.00 for a replacement bronze nut from a Colchester supplier, it made me laugh at first..

      Anyway, I am attempting to replicate the nut, a 3/4"-5TPI LH ACME thread with a round of Delrin I scrounged. I do have some moly powder on hand, supplied by Lyman for moly coating projectiles. It is very, very fine and the plan is to dust the lead screw before applying the Delrin halves.

      I only have one lathe now and its out of commission due to the cross slide lead screw being used for the Delrin nut , so considering the mill. Have a 8" R/T and tailstock to suit, do you think this can be used to true up the nut whilst on the screw and held with the R/T in the vertical position?

      I have not attempted anything like this at this stage, just used the R/T for milling arcs and bolt hole circles. Any tips on a suitable method I should look at using the above tooling?

      Many thanks,

      Mike

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      • Man, this thread sure has legs. Just stick the nut on the screw and put it in the lathe anyway. Mount a tool on the cross slide by clamping it to whatever is handy on the slide and set it to the right distance. Depth of cut isn't a big deal with plastic. Keep in mind you need to run in reverse to prevent the nut unscrewing during machining. Put a spacer between the nut and the chuck jaws so you can cut to the end. Either mount the tool upside down or put it on the back. You can even mount it pointing straight up. The lathe won't care.
        Free software for calculating bolt circles and similar: Click Here

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        • When I machined mine I clamped the cross-slide by locking the gibs and used the compount to feed the tool in.
          Peter - novice home machinist, modern motorcycle enthusiast.

          Denford Viceroy 280 Synchro (11 x 24)
          Herbert 0V adapted to R8 by 'Sir John'.
          Monarch 10EE 1942

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          • Can i make my halfnuts the same way this was done?

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            • Sorry it was off topic. Ill try not to do that again.

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              • Originally posted by ogre View Post
                Sorry it was off topic. Ill try not to do that again.
                If you can make the nut you can cut it in half, how is that not on topic?
                whether or not that is a good idea is another thing,
                but one I would not mind hearing an answer to.
                (or at least experienced opinions )
                --
                Tom C
                ... nice weather eh?

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                • I completed the cross slide nut for my Clausing 5914 lathe that I posted a picture of the original nut and a drawing of of the new nut about a page back in this thread.

                  https://picasaweb.google.com/lh/phot...eat=directlink

                  https://picasaweb.google.com/lh/phot...eat=directlink

                  https://picasaweb.google.com/lh/phot...eat=directlink

                  I had limited space to work with and also needed the nut to be aligned well with the screw after the molding as doing additional machining on the nut after the molding wasn't an option.

                  I made the shell with holes machined to closely fit the .625" diameter lead screw so that during the molding it would clamp down right on the screw on both ends so that it would be aligned well.

                  It worked out really nicely. The molding went pretty easily, I used a propane torch with a small tip and heated the screw evenly all around on both ends while tightening the screws to clamp the shells to together. At one point the acetal got much softer quickly and it was easy then to tighten the shells until they were fully clamped metal to metal, during this tightening the plastic squeezed out of both the shell splits and the end.

                  The acetal inserts were .375" thick, I machined them to be a tight slip fit in the shells. The shell pockets were both .378" deep, giving about 0.006" clearance for some plastic to be able to squeeze through and bond the two inserts together and that appeared to work well.

                  As Evan recommended with this .625" 10 TPI screw I made the hole size in the inserts .050" less diameter, ie .575". I'll have to admit that visually it appeared that this diameter was too big and there wouldn't be enough plastic to fully mold around the screw but it was just about perfect, just a small excess of plastic squeezed out of the shell ends and sides.

                  The nut was very tight on the shaft after cooling, I had put high temp lithium grease on the shaft prior to the molding but I think most of it melted away. Getting the nut off took around 30 to 40 ft-lbs.

                  After removing the nut I sawed a split on just one side of it. This allowed me to adjust the compression of the nut on the shaft by putting shims between the shell halves and as the nut wears I'll be able to compensate for wear by reducing this shim thickness.

                  So far the nut seems very tough and durable and with this shimming for wear I expect its going last at least as long as I do.

                  Thanks again to Evan and the other posters who added additional tips on using this method, its a great way to make low cost zero backlash nuts. In my case this tightly molded shell approach allowed me to make a zero backlash nut in a space were I wouldn't have been able to fit a ballscrew type nut.

                  The nut is part of a CNC conversion on my Clausing 5914 that is going to be pretty nice as it will also allow full manual operation for quicky jobs. The mechanics/motors part is all completed and I'm working on the electronics now and when its completed I'll post pictures on the Clausing Yahoo forum for other Clausing owners that might be interested.

                  Paul T.
                  PaulT
                  Senior Member
                  Last edited by PaulT; 08-13-2012, 02:33 PM.

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                  • Nice work! I might be copying that for a Clausing 6913 in a week or two!

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                    • Just signed up for no other reason than to say how awesome this idea is. Since I don't have a lathe I can't make pretty round things as shown in the tutorial, so I had to come up with something more square-ish. My only regret is chasing the threads a little too much which gave me just a hair bit of backlash, but nowhere near the .04" I had before.

                      Many, many thanks to the OP for bringing this method to the masses.

                      My version:

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                      • Another Evanut goes to work.
                        Free software for calculating bolt circles and similar: Click Here

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                        • Duuude, that looks pretty nice but I can't quite figure out how it goes together, are the sides slotted so that the aluminum frame retains the nut or is that done just with a clamping force?

                          What machine is the nut for?

                          Paul T.
                          www.springtest.com

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                          • Looks like the screw hold the piece in place.
                            Free software for calculating bolt circles and similar: Click Here

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                            • Hey George, would you consider making this one sticky???
                              I'm here hoping to advancify my smartitude.

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                              • It's in the favourite threads sticky. There's enough stickies already.
                                Free software for calculating bolt circles and similar: Click Here

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