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Nylon(instead of delrin) for a feed nut?

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  • Nylon(instead of delrin) for a feed nut?

    I have a RF 30 clone(chester E30) that unfortunately came with unhardened feed screws, which have now worn in an area to the point where they have to be replaced.

    Since I was planing on mounting a dro on both the x and the y axis I was thinking of replacing them with appropriately pitched(2.5 mm) acme all tread and making new nuts for them by making a tap out of some of the all tread.

    I know that lots of DIY cnc'ers use nylon feed nuts and they do seem to hold up quite well as far as wear is concerned(albeit with lighter loads), which got me thinking

    I can of course buy some delrin or other acetal but I have this chunk of nylon that is 70mm across and about 300mm long and I was wondering if it might have sufficient strength and wear resistance to be used instead.

    I have enough of it to make a much longer feed nut(spreading the load out over a larger area) to compensate for the increased load so I was wondering if this might do the trick.

    Does anyone know if this would be "good enough"?

  • #2
    make the nut by heating the screw and pressing the nylon around it. might be a little tight.

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    • #3
      Small note, a longer feed nut may start to reduce your travel.
      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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      • #4
        The way I figure it I have at least half the with of the y carriage as far as space for the x axis nut, less with the y axis but at least enough room to make a nut that is 2-3" long.

        I have enough space(and a second slightly smaller mill to re-machine mounting surfaces/clearances), provided the nylon proves to be a good enough material for a feed nut...........

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        • #5
          Originally posted by dian
          make the nut by heating the screw and pressing the nylon around it. might be a little tight.
          Might be tighter than you expect.
          Nylon (66) is one of a few materials that has a very sharp melting point rather than a melting range which most materials exhibit, and in this case it is 263deg C.
          The HDT - heat deflection temperature under load - or the point at which you can soften and deform it, doesn't really kick in until you're between 5-10deg from the melting point.

          So the upshot would be that you would probably need to control the temperature far more closely than such a process would allow, and require far more force.

          Whilst I don't actually agree that the same method using Acetals is a good thing (mainly due to the materials ability to re-crystallise itself and hence change it's size quite dramatically), it is however infinitely easier, as you have a melting range of around 20deg C to play with, and an HDT that starts around 100deg C.

          Peter

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          • #6
            Something to be aware of also is that any variations in the thread pitch (and there will be lots in anything less than ground rod) will cause problems in a longer nut. If there is 0.001" per inch of inaccuracy a three inch nut will bind and of course be re-machined by the rod. You'd quickly wear it out.

            This long nut problem was revealed in a recent conversation I had with the friendly and helpful Lars Romine of Horshpool & Romine in California, purveyors of everything acme to the gentry.

            Greg Q

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            • #7
              I made an acetal nut back when Evan put up his how-to thread, and although I didn't make a superb job of it (I got it too hot) it's still in service now. When I first made it, the action was quite tight and moreso at the ends of travel, but nowadays it's nice and smooth in operation and still has no backlash.
              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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              • #8
                Plain nylon has 1.4 times higher friction coefficient compared to acetal. It is also severely degraded by isopropyl alcohol and particularly propanol. Propanol is a component of many water mixed cutting lubes and coolants. It is also used in antifreeze.

                Nylon also has a high water absorption factor, around max 9% by weight for Nylon 6. At 50% relative humidity it will stabilize at a 1% change in dimension from the dry state. That takes a week or so. At 90% humidity it will grow by 3 to 4% after several weeks compared to the dry condition. As it dries out it shrinks back again.

                Acetal doesn't absorb water in any significant amount. It also has much better properties in some areas, 3 times higher abrasion resistance and 4 times higher resistance to deformation under load. It also unaffected by propanol.
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                • #9
                  Agree, acetal (Delrin) is a better choice than nylon. Size changes due to moisture absorption can be a problem with nylon. For a long nut, size changes may mean pitch changes which in turn means fewer thread in contact resulting in less stiffness and higher wear.

                  Magnitude of these effects may or may not be significant depending on the specifics of your application and the environment. High load and lots of humidity swings will be worse than low loads and constant humidity.

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                  • #10
                    How about a roller nut?

                    Minimum Friction and backlash, simple DIY job with a lathe:

                    RF30 mods

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                    • #11
                      Can you give us a synopsis, BillTodd? If I follow the links I end up on page 31 of a 67 page thread about something.

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                      • #12
                        Originally posted by Tony Ennis
                        Can you give us a synopsis, BillTodd? If I follow the links I end up on page 31 of a 67 page thread about something.
                        Ah they had a bit of reorganisation :

                        My contribution starts at post 429 page 36
                        http://www.cnczone.com/forums/linear..._screw-36.html

                        It's probably worth reading through it.

                        Basically it's a design of rolling form nut the rollers on the nut have grooves that engage with the lead screw tread; as the screw turns the rollers roll around the thread helix like a nut. The rolling motion removes most of the sliding friction allowing eccentric cam adjusters to keep the rollers in tight, back-lash free, contact with the thread.

                        I've had them on the X & Y axis of my drill/mill for nearly three years now and they work great.

                        Design PDFs of the X & Y nuts:

                        http://www.cnczone.com/forums/555769-post613.html
                        http://www.cnczone.com/forums/556324-post621.html

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                        • #13
                          Originally posted by BillTodd
                          How about a roller nut?

                          Minimum Friction and backlash, simple DIY job with a lathe:

                          RF30 mods
                          Very impressive Bill. Especially adding a Reeve's vari-speed drive to the mill/drill!
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                          • #14
                            Not tried it on any machine tools yet,but I have made some lead screw nuts out of MDS filled Nylon that worked perfectly for a screw actuator.

                            Antenna actuator for a boat,SS lead screw along with the MDS means no need for lubrication.
                            I just need one more tool,just one!

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                            • #15
                              Filled Nylon is an entirely different animal. It's available with molybenum disulphide, oil, graphite and PTFE, fibre glass and a few other materials. Each has very different properties compared to plain nylon and they all cost more too.
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