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Question for the acetal nut guys

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  • Peter.
    replied
    The sliding-mesh gears in my lathe are acetal and haven't chipped so far.

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  • Toolguy
    replied
    Leadscrew

    The Acetal is pretty tough and the thread form is tapered so it will engage easily. A square thread might be tricky to get going, but not Acme.

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  • form_change
    replied
    Once engaged an acetal nut will probably work just as well. However, acetal is one of the more brittle plastics from memory. I'm wondering if the initial engagement of the nut on the leadscrew may cause problems and the nut eventually get shipped away?

    Another thought is that an acetal nut as described is a very close fit. While great for minimum backlash, the fit may be too good to easily engage on the leadscrew.

    Just a couple of thoughts

    Michael

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  • Evan
    replied
    Nylon changes size by up to 5% depending on humidity. Acetal doesn't absorb water and is very stable.

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

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  • PaulT
    replied
    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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  • 1-800miner
    replied
    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.

    Leave a comment:


  • JeffKranz
    replied
    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.

    Leave a comment:


  • Peter.
    replied
    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.

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  • Duffy
    replied
    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.

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  • Rustybolt
    replied
    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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  • batt-man
    replied
    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

    Leave a comment:


  • Black_Moons
    replied
    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"

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  • Evan
    replied
    Acetal is completely resistant to mineral oils and greases as well as most common fluids except for acids.

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  • darryl
    replied
    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.

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