Trapezoidal thread form nut fix





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  1. #1
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    Default Trapezoidal thread form nut fix

    I bought an old Rockwell radial arm saw. The only issue was that the blade height could not be set. I stripped it this morning and found that the thread in the alminium block that the lead screw runs trough is completely stripped.

    Anyone with and lead where I can get this fix?
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    Last edited by Tiaan Pot; 2019/10/12 at 09:47 AM.

  2. #2
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    Default Re: Trapezoidal thread form nut fix

    Fit a Wurth insert.
    Sent from my iPhone


  3. #3
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    Default Re: Trapezoidal thread form nut fix

    Finding a machinist who can cut an internal thread in an alu block like that, might be a challenge in today’s world....but they are still out there.

    As a temporary “fix” you could use length of threaded bar with a nut on each side of the block....be a bit of a pain to adjust blade up and down....also won’t work if shaft is enclosed in a tube like my Dewalt radial arm.

    Have a great day

  4. #4
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    Default Re: Trapezoidal thread form nut fix

    I doubt it is trapezoidal.Do rockwell not make spare nuts. ?Thats also a left hand nut.So its going to be hard to buy a thread for it. I would start by trying to measure what pitch and diameter it is.

    A couple of ways to do it.
    1)buy new one
    2) Find engineering firm who can make a nut.
    3) find a mate who could either make a nut by single point turning it or making a acme left hand tap so you can machine tap it.
    4)try to get a left hand threaded bar similer
    5) Use standerd threaded bar but then it will turn anti clockwize.
    6) google a thing called an EVANNUT. I dont know how many forces are involved here.

    I would check to see if its left hand thread?
    I think banggood sell left hand taps for acme at good prices.

  5. #5
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    Default Re: Trapezoidal thread form nut fix

    OK so I educate myself a bit.

    Seems to be a T16 lead screw with a 3mm lead.

    So I need a nut for that. I will phone around Monday but it seems like I will now have to buy a lathe to fix my radial arm saw.

  6. #6
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    Thumbs up Re: Trapezoidal thread form nut fix

    Quote Originally Posted by Rebel 4x4 View Post
    Fit a Wurth insert.
    I looked at their catalog, does look like they do lead screw nuts insets

  7. #7
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    Default Re: Trapezoidal thread form nut fix

    Quote Originally Posted by Andrepb View Post
    Finding a machinist who can cut an internal thread in an alu block like that, might be a challenge in today’s world....but they are still out there.

    As a temporary “fix” you could use length of threaded bar with a nut on each side of the block....be a bit of a pain to adjust blade up and down....also won’t work if shaft is enclosed in a tube like my Dewalt radial arm.

    Have a great day
    The Rockwell looks exactly the same as the Dewalt just older. Think this one if from 1980 something.

    The cast iron arm is heavy hence why this one stripped so I'm not sure a normal thread will not work to well.

  8. #8
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    Default Re: Trapezoidal thread form nut fix

    Quote Originally Posted by plunger View Post
    I doubt it is trapezoidal.Do rockwell not make spare nuts. ?Thats also a left hand nut.So its going to be hard to buy a thread for it. I would start by trying to measure what pitch and diameter it is.

    A couple of ways to do it.
    1)buy new one
    2) Find engineering firm who can make a nut.
    3) find a mate who could either make a nut by single point turning it or making a acme left hand tap so you can machine tap it.
    4)try to get a left hand threaded bar similer
    5) Use standerd threaded bar but then it will turn anti clockwize.
    6) google a thing called an EVANNUT. I dont know how many forces are involved here.

    I would check to see if its left hand thread?
    I think banggood sell left hand taps for acme at good prices.
    Thanks plumber.

    This saw is pretty old so spares are impossible to find. The bang good suggestion was almost there. They do have T16 lead screw nuts but for a 4mm lead an mine has a 3mm lead

  9. #9
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    Default Re: Trapezoidal thread form nut fix

    If its 3 mm Its trapezoidal.Whats the diameter

  10. #10
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    Default Re: Trapezoidal thread form nut fix

    ACME thread.
    Any fair machine shop can make up a new nut.
    What area are you in?

  11. #11
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    Default Re: Trapezoidal thread form nut fix

    I must check my stock, I imported ACME left hand rods and nuts about 8 years ago that I've never used. Same as the ones used in the Maggiolina tent. What's the chance it's the same size?? I'll check on Monday. email me a reminder please - [email protected]

  12. #12
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    Default Re: Trapezoidal thread form nut fix

    If its american or british and old it will be imperial.This is important cause then you can work out the tpi.i guess thats 8tpi.
    If its metric it will be a 30 degree thread not 29.i could try make it i have made a nut for my lathes tailstock..i dont think there is much force on this as it doesnthave to clamp

  13. #13
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    Default Re: Trapezoidal thread form nut fix

    Quote Originally Posted by plunger View Post
    If its 3 mm Its trapezoidal.Whats the diameter
    Please excuse my $3.99 bang good special Caliper but at least its better than my CNA ruler.

    These are dimensions
    30mm over 10 threads so 3mm per thread?
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  14. #14
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    Default Re: Trapezoidal thread form nut fix

    Quote Originally Posted by Jakiesespeelding View Post
    ACME thread.
    Any fair machine shop can make up a new nut.
    What area are you in?
    Johannesburg for the forseable future.

  15. #15
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    Default Re: Trapezoidal thread form nut fix

    Quote Originally Posted by Heinz Modricky View Post
    I must check my stock, I imported ACME left hand rods and nuts about 8 years ago that I've never used. Same as the ones used in the Maggiolina tent. What's the chance it's the same size?? I'll check on Monday. email me a reminder please - [email protected]
    Thats would be awesome. I'll definitely send you an email.
    Thanks you Hein

  16. #16
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    Default Re: Trapezoidal thread form nut fix

    15.8 (15.875) is imperial 5/8's. I think I would have nought metric 20mm, but it's worth a shot looking.

  17. #17
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    Default Re: Trapezoidal thread form nut fix

    Set your vernier to 25.4mm and count how many threDs fit in it.then measure ffrom the middle of one thread to the middle of another.or use a pitch gauge
    Tpi is threads per inch.metric will be from one thread to another.safer to measure from edge to esge

  18. #18
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    Default Re: Trapezoidal thread form nut fix

    Thank you everyone for all the advice.

    So I'm now pretty sure it's a 5/8 inch 8 TPI Acme nut that I need. It seems like I can get one easily from most local nut and bolt shops.

    Just one last question ( please don't laugh)

    Does it matter if the nut is right hand thread on my left hand thread screw?
    Last edited by Tiaan Pot; 2019/10/13 at 09:24 AM.

  19. #19
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    Default Re: Trapezoidal thread form nut fix

    If shaft is LH, then nut must be LH.

  20. #20
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    Default Re: Trapezoidal thread form nut fix

    I would be very suprised if you can get a left hand nut.
    Can you take a picture of your saw so we can see what it looks like.Sometimes you can split a nut and get a bit more life out of it. If you get a hacksaw and cut through the diameter of the thread and put a bolt through so you can pinch it then you may get some more life out. But if its completely stripped ,no chance.
    How much dismantling did you have to do to get the leadscrew and nut out.

    Does it look anything like my old rockwell?
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    Last edited by plunger; 2019/10/13 at 12:10 PM.

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