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Thread: Threading confusion. A bit long.

  1. #11
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    Quote Originally Posted by gnm109
    (Are you quite certain that you didn't sneeze during your measurement of the leadscrew. )
    HaHa

    Yes quite sure.

    I can see you guys don't believe me and quite frankly, I don't blame you.
    Here's a pic.
    I hope it's good enough.
    You'll have to trust me that the calipers displayed zero when closed.


    Let's open bidding on an impossibly odd leadscrew(almost new). Start at say $2500.

    Mike
    Mike

    If you buy crap, be prepared to re-design and fix it.

  2. #12
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    Quote Originally Posted by Peter.
    Sure it's not a 6tpi and you're counting the crest on both ends of the inch to get 7?
    Yes, I'm familiar with wavelength and know that I need to measure between identical points on the curve. Also, an error like that would become quite small over 10".

    Mike
    Mike

    If you buy crap, be prepared to re-design and fix it.

  3. #13
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    I wonder how much it would cost to replace with a 8TPI lead screw?
    Could that be metric? I guess you can always thread by just leaving
    the dial engaged between passes.

    Beautiful picture.

  4. #14
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    Quote Originally Posted by Blueskys
    I wonder how much it would cost to replace with a 8TPI lead screw?
    Could that be metric? I guess you can always thread by just leaving
    the dial engaged between passes.

    Beautiful picture.
    If it was metric wouldn't that have shown up over 10"? I counted the threads over 10" and got 70 (exactly).

    I only had to leave the half nut engaged when cutting a metric thread. All the other threads were cut the easy way.

    If I changed the leadscrew I'd have to get different change gears and the chart would be all wrong and that seems like a really bad plan.

    It's just a Chinese lathe.
    I'm very impressed with it's performance and I'm really not complaining one bit. I just want to better understand the way the thread dial works.

    Thanks to everyone for the replies.

    Mike
    Mike

    If you buy crap, be prepared to re-design and fix it.

  5. #15
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    Louisville, KY
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    The only thing I can think of is for you to hit a yahoo group specific to your lathe and ask there.

  6. #16
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    Just out of curiosity, what is the make and model of the lathe??? Or did I miss that??
    Ernie (VE7ERN)

    May the wind be always at your back

  7. #17
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    Quote Originally Posted by dockrat
    Just out of curiosity, what is the make and model of the lathe??? Or did I miss that??
    Didn't say this time.

    I have a Craftex from Busybee. B2227L 10" x 18"


    Mike
    Mike

    If you buy crap, be prepared to re-design and fix it.

  8. #18
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    Fascinating, a 7 TPI lead screw!

    I guess there is no immutable law that a lead screw HAS to be 8 TPI (or some other easy to work with number) on an imperial lathe.

    Edit. For a company that makes metric and imperial lathes, is choosing a 7 TPI lead screw something to do with 18 x 7 = 126 which is nearly 127 which is the metric/imperial conversion factor?
    Last edited by bob ward; 01-10-2010 at 06:55 PM.

  9. #19
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    citrus heights, ca
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    Quote Originally Posted by MotorradMike
    Didn't say this time.

    I have a Craftex from Busybee. B2227L 10" x 18"


    Mike
    That's the same lathe that Airsmith has, and he has 250,000 hours on his. I'll bet He could tell You everything You ever wanted to know about that lathe .
    Well, everything except what a carrage stop is .
    Steve

  10. #20
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    Jun 2004
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    Anniston, AL
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    I agree that a 7 TPI leadscrew is unusual but there is no reason it should be a problem in regards to the thread dial. All you need is a 28 tooth gear to measure the same 4 inches that a 32 tooth gear measures on an 8 TPI leadscrew. Possible engagement points differ slightly since you can't engage the leadscrew at 1/8th revolution (1/2 inch) points there can be only 4 usable marks on the dial. The gearing to change the threading pitch would of course be different but easily accomodated.

    With a 7 TPI leadscrew all threads which are multiples of 7 (7, 14, 21, 28, 35, 42, 49, 56, etc.) can be cut without a thread dial. Any place the half-nuts will engage the leadscrew is okay.

    I wonder if the OP has measured accurately enough to tell that the screw is not actually 3.5 or 3.6 MM? Seven turns of a 3.5 MM screw is less than 1 MM from being an inch. (Edit: It seems he has since he measured over 10 inches.)

    Don Young
    Last edited by Don Young; 01-10-2010 at 09:36 PM.
    Don Young

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