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    Default Threads Skewed

    Newbie here. Hobby fabricator/machinist.
    My difficulty is that my thread shape is not to my satisfaction. The shape of the triangle formed has the apex shifted toward the headstock such that the headstock side angle is steeper than the tailstock side.
    Threading left to right, A thread, inverted 60* carbide insert, mild steel.
    The thread works on the tapped female thread, but I know it has a lot of room for improvement!
    I was considering taking lighter cuts once I get into the “meat” of the part as a possible way to improve on this aspect.
    Any suggestions welcomed.
    Appreciated

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    Quote Originally Posted by gtj View Post
    Newbie here. Hobby fabricator/machinist.
    My difficulty is that my thread shape is not to my satisfaction. The shape of the triangle formed has the apex shifted toward the headstock such that the headstock side angle is steeper than the tailstock side.
    Threading left to right, A thread, inverted 60* carbide insert, mild steel.
    The thread works on the tapped female thread, but I know it has a lot of room for improvement!
    I was considering taking lighter cuts once I get into the “meat” of the part as a possible way to improve on this aspect.
    Any suggestions welcomed.
    Appreciated
    wrong 29.5 degrees?

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    If your tool is truly a 60 deg form, then you need to adjust it parallel to the axis of the shaft.
    A fishtail works good for this.

    ^Also check what he said.

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    Quote Originally Posted by janvanruth View Post
    wrong 29.5 degrees?
    Yep. Probably this.

    Point the compound straight in to the work, then swing it to the appropriate side, by 29 degrees, not to the 29 degrees mark.

    Then use the fish plate gage to set the tool square with the work.

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    So it looks lie this but is about a half degree short (right of) of the big line. Not past the line.
    lathe turning threads compound angle - Yahoo Image Search Results

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    Quote Originally Posted by trevj View Post
    Yep. Probably this.

    Point the compound straight in to the work, then swing it to the appropriate side, by 29 degrees, not to the 29 degrees mark.

    Then use the fish plate gage to set the tool square with the work.
    OK, Lightbulb moment. Got it!
    Makes sense. 29.5 to the part, not the dial setting. Dial setting would be 60* if using a 30* angle.
    Thank You Kindly.

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    Default Thanks Men!

    Thanks Everyone.
    Much Appreciated.
    Can't wait to make some better threads.
    Cheers

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    Quote Originally Posted by gtj View Post
    OK, Lightbulb moment. Got it!
    Makes sense. 29.5 to the part, not the dial setting. Dial setting would be 60* if using a 30* angle.
    Thank You Kindly.
    Cool!

    Have fun! Learn stuff!

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    I made this drawing a few days ago for another thread. It explains it in pictures:


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    Can we make this thread a sticky?
    We went from problem statement to clear explanation in 9 posts.
    Awesome work.

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    I like to visualize an equilateral triangle looking down at the ways. The ways forms one leg of the triangle, and the compound the other. If what you visualize is not an equaliateral form, then stop and readjust.

    I made the mistake working on a lathe on which I'd never cut threads on before. Thankfully about 4 passes in I realized it was "shaped wrong" and had enough meat left to get the correct threadform by the end.

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    GTJ, nice to have you aboard PM. Where are you in Ontario?
    Buck

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    Quote Originally Posted by matt_isserstedt View Post
    I like to visualize an equilateral triangle looking down at the ways. The ways forms one leg of the triangle, and the compound the other. If what you visualize is not an equaliateral form, then stop and readjust.

    I made the mistake working on a lathe on which I'd never cut threads on before. Thankfully about 4 passes in I realized it was "shaped wrong" and had enough meat left to get the correct threadform by the end.
    I am always amazed more of this visualization or mind's eye responses are not far more common

    Just blow up the thread flank in your mind's eye and it will be very suggestive of where the compound needs to be to follow that flank

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    Quote Originally Posted by Erich View Post
    Can we make this thread a sticky?
    If this needs to be a sticky then we are fuckin doomed.
    This is honestly the first time all my years in this field that I've heard of someone using the wrong 29 deg angle for threading.

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    Quote Originally Posted by Mtndew View Post
    If this needs to be a sticky then we are fuckin doomed.
    This is honestly the first time all my years in this field that I've heard of someone using the wrong 29 deg angle for threading.
    Or so many guys having this problem...I think How to Run a Lathe gives advice on this. I will check.

    Yes it does, my copy on page 77 with a photo of the compound at correct angle, written text, and showing the tool bit advancing.

    With looking at that page one would never do it wrong.
    And the soft cover reprint is only about 5 bucks.

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    I hope this actually solves the problem the OP is having.

    If you look at his original description, though, it is opposite of what would occur from having the compound at 60 degrees to the ways. If he did that, the steeper flank would be toward the tailstock, not toward the headstock.

    And, OP, regarding your comment, "Dial setting would be 60* if using a 30* angle.", that is incorrect. The dial setting would be 60 degrees if you were threading a 120 degree included angle thread.

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    But 866 x p being so easy is perhaps why new guys want to go that way..

    I made a sheet that shows at 30* and at straight in (yes at 30 is close enough to use at 29 1/2*

    it would be nice if someone published such a sheet

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    Quote Originally Posted by Mtndew View Post
    If this needs to be a sticky then we are fuckin doomed.
    This is honestly the first time all my years in this field that I've heard of someone using the wrong 29 deg angle for threading.
    why do think i came up with the answer so readily?

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    Quote Originally Posted by Mtndew View Post
    If this needs to be a sticky then we are fuckin doomed.
    This is honestly the first time all my years in this field that I've heard of someone using the wrong 29 deg angle for threading.
    Pretty easy to figure out who has, and has not, taught newbs how to run a lathe, innit!

    The 'wrong' 29 degrees, is pretty much a go-to, for new operators.

    Next most common would be getting a massive step in the side of the thread, from not getting the half-nuts fully engaged, ending up with a stair-step thread profile.

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    I have seen operator manuals that give advice. One a not-to-mention lathe has very good treading advice.


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