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Thread: Is There a Machinist in the House?

  1. #1
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    Is There a Machinist in the House?

    I have a question about Acme screws and nuts. Is there are standard chamfer angle used on the ends of Acme-threaded screws and on the opening of the mating nuts? Is there a standard for treating where the threads end? I had a request to show how to draw a detailed screw and nut in SketchUp. The requester is interested in drawing up some threaded thing for 3D printing so I'd like to show finishing the ends correctly. Here's the screw I've got so far.



    I put a 14.5 chamfer on the ends but it leaves the end of the thread quite sharp which I expect in reality would be problematic.

    Normally I don't care about such details because I only need to show that something is threaded. I never bother with internal threads since they don't show but, this is an exception.

    Thanks in advance.
    Irony: The opposite of Wrinkly

  2. #2
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    dave on my bench vice its a sharp end no bevel..
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  3. #3
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    As far as I know from years in the trade as a design and manufacturing engineer - there is no standard. I could look in the machinery data handbook later - but an internet search may be just as good.

    Yes - it will end with a sharp thread.

    If I were going to get really fussy, ans have the steel in my hand, I will walk up to a bench grinder with a fine wheel and break down the sharp edge. I may also grab a file - and some emery cloth.

    It would be most common to make a 45 degree chamfer on the end where the small diameter of the chamfer would be at or smaller than the root diameter of the thread.

    There are really no hard fast rules.

  4. #4
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    Thanks guys. Questions answered.

    Cheers.
    Irony: The opposite of Wrinkly

  5. #5
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    limited dealings

    Quote Originally Posted by Dave Richards View Post
    I have a question about Acme screws and nuts. Is there are standard chamfer angle used on the ends of Acme-threaded screws and on the opening of the mating nuts? Is there a standard for treating where the threads end? I had a request to show how to draw a detailed screw and nut in SketchUp. The requester is interested in drawing up some threaded thing for 3D printing so I'd like to show finishing the ends correctly. Here's the screw I've got so far.



    I put a 14.5 chamfer on the ends but it leaves the end of the thread quite sharp which I expect in reality would be problematic.

    Normally I don't care about such details because I only need to show that something is threaded. I never bother with internal threads since they don't show but, this is an exception.

    Thanks in advance.



    Dave,

    I have cut hundreds of valve stems from one inch acme threaded stock and also threaded hundreds of acme threaded hubs. Might run into thousands, no real count on how many of each I have made in short runs of a hundred or two at a time. Guess I have done low thousands of the stems when I think about it. I have cleaned up the ends on six or eight hundred stems of different lengths in a single day.

    Anyway, the stems are chamfered slightly as you have done and then touched to a wire wheel to remove the razor edge that can fold over and cause problems. The ends are quite sharp and will cut you if handled carelessly. The rolled acme threads themselves are often sharp enough to cut you also. The threaded stock was stainless, I think 304 or 316 depending on usage of the valve but I may be mistaken concerning the alloys, been years since I was doing this.

    On a one off job I would grind the sharp point back a little and grind a slight taper from the end back on the outside to make the threads easier to start and a little safer to handle. Short run production they just get cranked out, the people doing assembly are used to handling the stock and know the dangers.

    Since you are striving for accuracy I will comment on a tiny error that appears to be in your drawings. The external diameter on the ends should go away rather than flattening out and continuing around the arc. The issue is most obvious at the bottom of the vertical threaded stock. The ends will look asymmetrical when accurately portrayed. Overall an excellent depiction!

    I have long been a jack of all trades and master of none. Before an injury in '93, I checked all drawings produced by the drafting department at Waterford Three, the local nuke. Nit picking was my specialty. Pretty rusty now though.

    Hope this helps,

    Hu

  6. #6
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    Thanks Hu. The treatment of the end of the thread is one thing I was particularly asking about. I tried to find some photos of it but couldn't.
    Irony: The opposite of Wrinkly

  7. #7
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    i asked my acme specialist, but he had no reply....
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