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Question for the acetal nut guys

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  • Question for the acetal nut guys

    I just picked up an older Sheldon ten inch with a single half nut. The machine is sound but the half nut is worn.The lead screw looks fine.
    My question:do you think the acetal nut trick will hold up in this application?
    Or any other ideas?

  • #2
    Half Nut

    I think it would be worth a try. It might run for a long time.

    Comment


    • #3
      I am bumping this one to see if I can get some more responses.
      Just leery of plastic in this application.

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      • #4
        It isn't going to cost much to try. Briggs gas engines have acetal valve cams and most washing machines have acetal gears in the transmission.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          Used to install satellite dish actuators, rated between 600 and 2000 lbs. Most of them had plastic nuts. In the rare case where the leadscrews didn't rust (other failure mode developed) the nuts were relatively unworn. Once the leadscrews did rust though, it tore up the plastic nuts. Bronze nuts seemed to handle the rust better, but did not outlast the plastic ones when the leadscrews remained clean.

          There was one brand that was rated among the strongest in terms of thrust, and it seldom had a problem because the actuator rod was well sealed against moisture intrusion. It was the only one I believe that was made with aluminum tubing. It had an acme leadscrew, and when it was removed from service the plastic nut looked perfect. A new nut for another brand of actuator had more play on an unworn part of the leadscrew than this one did.

          Something else I noticed in this brand was that the grease was still there on the leadscrew. Whether is was a special grease, possibly something optimum for the plastic nut, I don't know.

          These actuators were designed to hold with constant pressure against the parts. In our part of the country (PNW) at the time, a few of the popular satellites were to the west. For the dish, this meant that the actuator had a hard job to do as the body of the actuator got close to the pivot point of the dish mount. If you drove it too far west, you'd have to help it out to get moving east again. The constant pressure on the nut, and powering the actuator with that pressure always on it would seem like a recipe for early wear and possible creep in the nut. Never seemed to be a problem though, except where as I mentioned, when the leadscrew started to rust.

          I can't fault the durability of the plastic nut in this application, and I doubt there would be a problem on a lathe or mill, unless swarf was able to contaminate the lube.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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          • #6
            Acetal is completely resistant to mineral oils and greases as well as most common fluids except for acids.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Originally posted by Evan
              Acetal is completely resistant to mineral oils and greases as well as most common fluids except for acids.
              'completely resistant' Seems a little bit of an oxymoron.

              Is it completely oil/etc 'proof' or unaffected, Or is it just 'Resistant'?

              Resistant to me is a lawyer term that means "It used to be water proof, But now its just water resistant, So don't blame us if its not water proof and happens to leak"
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                I seem to remember that Evan did a write-up on how he made some acetal-type half-nuts a while back?

                Just found it
                http://bbs.homeshopmachinist.net/sho...ead+screw+half

                Evan - It would be interesting to hear how that's been holding up for you?

                Cheers
                Batt

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                • #9
                  i don't think the object is its ability to withstand lubricants, but wether or not it can take the load of a heavy cut without stripping.

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                  • #10
                    The ability to survive heavy cuts is similar to the ability of a pinion gear to take heavy loads. If you accept that logic, Craftsman garage door openers use acetal pinions, and mine has had one replacement in 22 years operating a 14 foot door.
                    Even with couterbalancing springs, it represents a hefty weight.
                    I would expect the replacement half nuts to outlast the installer if this is a hobby-use lathe.
                    Duffy, Gatineau, Quebec

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                    • #11
                      I think that any load which could strip the thread from an acetal ACME nut would be bad for the machine altogether. It might be 'only plastic' but I wouldnt's fancy screwing an acme rod into an acetal nut and then trying to knock it out with a sledge hammer.
                      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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                      • #12
                        You might want to check with the company that has parts for Sheldon Lathes.

                        Sheldon parts: Sheldon Machine Company -Division of Acme Technologies Group-Po Box 949 2100 Cedar St. Fremont, OH 43420 phone: 800-553-2263 (parts)

                        You probably can get a parts manual from them if you ask nice.

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                        • #13
                          I had no idea that Sheldon parts were still available.I will call in the morning.
                          Thank you!

                          If I can't get the part,I have the acetal ordered.

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                          • #14
                            Originally posted by 1-800miner
                            I had no idea that Sheldon parts were still available.I will call in the morning.
                            Thank you!

                            If I can't get the part,I have the acetal ordered.
                            My memory is that this parts organization is being run by the son of the original owner. Based on your serial number they might be able to give you some historical info on your lathe.

                            Paul T.

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                            • #15
                              Can you use nylon 66 to make nuts as I have quite a bit of it?
                              MBB

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