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Making Acetal leadscrew nuts the easy way

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  • Originally posted by Evan View Post
    Another Evanut goes to work.
    Yes sir!

    Originally posted by PaulT View Post
    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
    You got it, its slotted on each side and the top.

    The machine is a RF30 I picked up a couple of months ago. Its my first actual mill, before that I was doing extremely scary and dangerous things on a drill press. Fingers are not fixtures!

    Now that the table nut has been replaced, the other feels miserably sloppy. I'm not a fan of the way it anchors in there, nor how you've got to tear the table off to get to its bolt. I'm scheming something entirely different for that one.

    Originally posted by Evan View Post
    Looks like the screw hold the piece in place.
    There are actually two, one on each side, and they kind of serve a not-planned-for purpose. The block is a tight enough fit into the frame that they weren't really needed, but at some point I absentmindedly cut the block .04-.05" too short and had to find a way to get it back up to where it needed to be. To do that I notched a little deeper on the top side, drove it further up into the frame, then drilled and tapped for a couple of #6 button heads to lock it into place.

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    • This truly is the thread that keeps on giving!
      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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      • How about using Turcite acetal?

        I see on McMaster-Carr's website that Turcite rods (red and blue) are listed under Acetal, and that they contain a silicone-based additive that makes them especially slippery.

        Although the price of Turcite is much higher than that of the generic acetal, it's probably not prohibitive, given the small amount of material needed to make leadscrew nuts.

        Would this material work using Evan's technique?

        Are there potential problems with toxic fumes or high temperatures?

        In terms of slipperiness, would Turcite offer an advantage over generic acetal if it can be used for leadscrew nuts?

        Here's a link to the MMC listing:

        Self-Lubricating Chemical-Resistant Turcite Acetal

        -Chris

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        • I didn't see it mentioned, but it seems like it would be easier to heat the screw up in the oven to temp first and then use the heat gun to maintain it if needed. This is assuming that the screw is small enough to fit in your oven.

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          • You could do that. However, unless the oven is in your shop, the screw will cool too much before you can clamp it into the two halves. Plus the mass of the screw is really too small to hold heat for very long, so you are probably better off starting with a cold screw and heating it after you have it clamped up.

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            • Turcite is a brand name and no longer refers to a specific material. The original Turcite is a PTFE plastic with fillers. Technically PTFE is a thermoplastic but it behaves like a crosslinked plastic. Thermoplastics melt when heated, crosslinked plastics do not. PTFE variants do not melt in any usable manner.

              Edit: There are a couple of PTFE variants that are specially designed to behave like a thermoplastic and can be injection molded.
              Last edited by Evan; 10-02-2012, 10:10 PM.
              Free software for calculating bolt circles and similar: Click Here

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              • Originally posted by oxford View Post
                I didn't see it mentioned, but it seems like it would be easier to heat the screw up in the oven to temp first and then use the heat gun to maintain it if needed. This is assuming that the screw is small enough to fit in your oven.
                I had a 5/8" screw on my cross slide that I made the nut for. I was much easier to heat up to the required temp than I thought it would be.

                I used a small hardware store type propane torch and just heated the screw as evenly as I could around each end of the nut.

                It was ready to go before I expected and once its up to right temp things happen fast, giving me an "oh sh**" moment but I was able to clamp the two sides together evenly and it came out fine.

                Paul T.
                www.springtest.com

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                • Thanks Paul, I saw the nut that you made, it came out very nice. I am attempting to make some for a 5914 as well. I am going to try and do the cross slide a little different so there is a little less machining.

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                  • I don't remember if I saw it or not but when using the acetal/delrin nuts should there be provisions for or does it need lubrication?

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                    • Acetal will run dry as long as the surfaces are polished. It may be lubricated with any usual petroleum based lube as well and it reduces friction. Either way is fine. This does not necessarily apply to other plastics.
                      Free software for calculating bolt circles and similar: Click Here

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                      • ok, and to clear something else up is delrin the same as acetal? I gathered that Delrin is just a brand name of acetal but is there anything special about it? I can sometimes get drop offs and short pieces of various "plastic" at work. Some of it is always referred to as delrin, I have never heard the term acetal there.

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                        • I finally got my Clausing 5914 CNC conversion up and running.

                          Its working really well. As shown in some previous posts on this thread I made an acetal nut for the cross-slide. On this machine space is very tight and using a full ballscrew and nut would have been an ugly hack. The acetal approach allowed me to use the existing lead screw and make a nut that fit in the small space available for the stock nut.

                          I very pleasantly shocked on how well its working. I'm seeing less than 0.001" of backlash, even with the so-so stock thrust bearings that are in the machine on the cross-slide screw. What's also nice is they way I implemented the nut I'll be able to easily re-adjust it for wear so it will always give me low backlash.

                          Having a combo CNC-manual lathe is working out way better than I realized it would, its even a way better machine now for quickie manual jobs also.

                          This was a pretty low-buck conversion as it used both the original lead screws and the steppers I'm using have plenty of power and speed, I don't it would be any better with servos, it moves fast enough for me with the steppers, 40 ipm on the cross slide and 90 ipm on the Z axis.

                          I'll post pictures of the conversion after I finish the gang tool bar I'm making for it.

                          Thanks again to Evan and the rest that contributed to this acetal nut method, it really works.

                          Paul T.
                          www.springtest.com
                          Last edited by PaulT; 03-23-2013, 03:59 PM.

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                          • ok, and to clear something else up is delrin the same as acetal? I gathered that Delrin is just a brand name of acetal but is there anything special about it? I can sometimes get drop offs and short pieces of various "plastic" at work. Some of it is always referred to as delrin, I have never heard the term acetal there.
                            Delrin is the DuPont brand name for acetal homopolymer. Acetal is the generic name for a very similar but NOT the same chemical compound which is a copolymer. For many purposes they are interchangeable but not for all. They have slightly different melting points which affects injection molding. Delrin tends to develop core porosity when molded in large sections, acetal copolymer does not. Delrin has greater strength than acetal by about 20% or so. However, acetal copolymer is reasonably resistant to attack by acids, Delrin is not.

                            This is very important to parts made for food processing where the parts are exposed directly to the food. Delrin will be strongly attacked by foods such as tomato ketchup, vinegar, orange and lemon juice etc. Regular acetal copolymer is suitable for such uses. Both compounds are very resistant to oils including petroleum based oils and to alkali compounds. They both have excellent impact resistance, exceeding that of mild steel. They are used in gears that run in oil baths such as in washing machines and have been used for decades for the cams in Briggs small engines.

                            Many places that sell plastic are not aware of the differences although they should be. They are definitely not the same. For the purpose of making lead screw nuts either will do just fine.

                            Nice to read another success story Paul.
                            Free software for calculating bolt circles and similar: Click Here

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                            • Hey guys GREAT thread!

                              I am looking for suggestions for the repair of my Y axis lead screw nut. I want to do the acetal repair but I'm not sure what the best method would be in regards to the design of my nut. I'm posting some pictures hoping that some of the wizards on here give me a flake of wisdom. I have access to a worn out old Bridgeport and a 9 x 20 HF lathe.

                              I was thinking about milling out this nut to accept a square of Acetal, but now I am wondering if starting from scratch with a raw block would yield better results. Also, I don't have much headroom unless I mill out the bottom of my table, so that is out of the question.

                              Thanks for any response,

                              pics:

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                              • Ok.... I haven't done this yet, but I've given it some thought, as I have a sloppy feed nut to replace...

                                I was thinking I'd make up a pair of half-pipe sections in steel as a "press" to fit around the acetal, a little larger ID than the finished nut insert OD, turn the acetal blank to fit then bore to slightly smaller ID than the screw pitch diameter, and split longitudinally so it can be clamped around.the screw. Once all assembled, put in the vice or a press and heat the screw until the acetal flows and fuses. Once cooled, peel off the half-pipes (might be worth using a release agent, silicone?) and true the nut insert in the lathe, centring off the screw, finally bore the remains of the original nut and bond in the acetal insert.

                                Dunno whether it would work, but planning to give it a go!

                                Dave H. (the other one)
                                Rules are for the obedience of fools, and the guidance of wise men.

                                Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

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