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  1. #1
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    Default casting a brass nut

    Hi all .. Had this in the general section.. some may already have seen it..I need to reproduce this nut for a vintage vice I am working on.. thread diameter is 7/8" or 22.2 mm.. pitch is just over 4 turns to the inch..
    because of the mystery number of turns, and as it is brass, would it be possible to cast a new nut around the screw ???
    Ken100_3138.jpg100_3140.jpg100_3137.jpg

  2. #2
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    Default

    If you were to cast the nut around the bar, you would possibly have a dickens of a job getting it off, as when metal cools it shrinks, causing it to tighten on the shaft.
    The best way would be to make a sand plug of the nut. The hardest part would be making allowance for shrinkage, as normally the threads are machined afterwards.
    Would you be looking at getting it cast commercially? If so, contact them or a patternmaker, as they would know the shrinkage rate of brass.
    Hope this helps,
    Kryn
    To grow old is mandatory, growing up is optional.

  3. #3
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    As Kryn suggests, casting the nut around the screw would not be easy. Apart from getting it off (casting hot metal onto a 'cold' screw - natural thermal shrink fit), you would have to choose a length of thread to cast onto that was the most unworn with no surface defects for the hot metal to grab onto. Sealing off the surrounding thread so the liquid metal did not sneak down there is another thing, and you would also be hoping that the metal was fluid enough that it would accurately fill the space between the threads. Not impossible, but not easy either.

    From experience I've found that foundry casting is not cheap either. No fault of theirs, but things cost. As an example, I looked at getting a CI casting done recently. I would spend several days making a pattern, they would take some weeks to get to it then charge me a few hundred dollars for the privilege. I bought a billet of CI that I could machine the part out for around $60.

    Machining a nut like that from solid is not difficult. I'm doing a couple this weekend (I hope), and I did an ACME bolt/ nut combo last weekend.
    P1040581.JPG
    I would suggest cutting the thread then rough out the blank on a lathe. Finish with a bit of filing and the chances are no one will ever notice that it is not the original.

    Michael

  4. #4
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    To add to what Michael mentioned, if you want to be a real stickler for authenticity, when you've finished machining it, go crazy with a prick punch on just keep tapping it to give that cast look.
    Kryn
    To grow old is mandatory, growing up is optional.

  5. #5
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    Default

    Needle gun it is much quicker

  6. #6
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    Default

    True, but not everyone is into tattoos, plus not everyone has one for metal either.
    Kryn
    To grow old is mandatory, growing up is optional.

  7. #7
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    Default

    I think the issue here is the thread is not standard, at least it doesn't seem to be.

    Know anyone with a cnc lathe or at least electronic lead screw?



    Russ

  8. #8
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    Quote Originally Posted by russ57 View Post
    I think the issue here is the thread is not standard...
    Doesn't matter. On my lathe, with a combination of change wheels and the box on my lathe, just about any thread is possible. Some others would have lathes of similar abilities. If your lathe only has a QC gearbox you may be in trouble if the pitch needed is not native to the lathe but other than that, cutting a nut is not much more difficult than cutting an external thread.

    CNC or ELS makes it quicker but is not a deal breaker for reproducing a less common thread.

    This is a nearly completed 1", 4mm pitch LH nut being cut on a lathe with an imperial leadscrew. I could swap some cogs and cut 15.237 tpi just as easily.

    P1040587.JPG
    Michael
    Last edited by Michael G; 25th May 2019 at 10:29 PM. Reason: Added picture

  9. #9
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    Default

    There is some stuff online for lathe attachments to adjust the pitch of the thread being cut, but I never got around to making one, despite having a need for cutting odd threads on occasion.
    From the archives:
    jacquesmaurel.com/machining
    www.model-engineer.co.uk/forums/postings.asp?th=84148&p=1
    www.youtube.com/watch?v=3wULa5aTPd0
    www.mccrone.com/mm/an-adjustable-threading-feed-attachment-for-a-lathe-without-metric-threading-capability/
    Ted McDuffie's 'Variable Lead Threading Attachment' | Model Engineer

    Apparently the geometry of the setup gives quite consistent thread pitch, provided that the screw being cut is not too long.

    Cheers,
    Bill

  10. #10
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    Default

    Not a direct answer to the original question, but I recall a while back reading an article about forming one of the engineering plastics(name escapes me ATM) around a leadscrew to repair a flogged nut.
    EDIT: It was Acetal and the article was on homeshopmachinest forum.

    Might be an option if you're just looking to return the lathe to serviceability rather than an exact restoration.

    Steve

  11. #11
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    Default

    This is for a vise, no idea if plastic would be suitable. Love to know though!

    Russ

  12. #12
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    Default

    Quote Originally Posted by russ57 View Post
    This is for a vise, no idea if plastic would be suitable. Love to know though!

    Russ
    I'm not sure either, but I can tell you that they make the point sheaves on some cranes out of plastic, (my guess would be Acetal/Delrin) and the one I have seen was on an 80 tonne crane, and the sheaves would have been about 600 mm in diameter from memory. Of course on your vice, the loading may be much higher than it is on the crane (in terms of PSI say) because although the crane load was much greater than you would get on the vise, there would have been many more square inches to support it. Again a WAG, but the shaft through the sheave was probably around 70 mm in diameter.

  13. #13
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    Default

    Thanks guys.. I may have to cast a nut blank and machine it to suit a newly made screw of standard pitch.. either way i need a solid casting made of the nut..
    Is anyone interested ?
    Ken.

  14. #14
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    For a onesie you'll be better off just machining one from bar stock I would think. Pretty hard to lay eyes on a vice nut so noone will know.

    Sent from my Nokia 8 Sirocco using Tapatalk

  15. #15
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    Default

    If you haven't repaired it already perhaps this different Solution will work.

    Run a bit of soft solder into the nut, and sharpen the end of your threaded "bolt" as shown on the Practical Machinist website here: https://www.practicalmachinist.com/v...g-taps-187694/

    If the expected service is arduous, use silver brazing rod (silver solder) instead.

    In both cases a good cleaning would be required before you start.

    Regards,
    Alan.

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