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Thread: Threading confusion. A bit long.

  1. #11
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    Nov 2009
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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

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

  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

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

  3. #13
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    Nov 2009
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    Northern Michigan
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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

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

  5. #15
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    Oct 2009
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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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    Ashcroft, British Columbia
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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

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

  8. #18
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    Jun 2007
    Location
    Laidley, SE Queensland
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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 07:55 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 10:36 PM.
    Don Young

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