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Author Topic: lathe threading pitch error  (Read 10898 times)

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Offline RICH

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Re: lathe threading pitch error
« Reply #30 on: January 21, 2013, 07:15:04 PM »
fast89,
- Do scribe test's for reasons I mentioned. The scribe tests that i did were used to measure pitch to 0.0002" and
  you don't get that from comparison to a tap. The tolerances are noted in threading on the lathe manual, page 26.
  So for a 1/4-20 the error allowed for a 2A over .3" is 0.001". Said a different way.....one thread is 0.50", .3"/.050"=6 threads,
  thus 0.001" allowed. If 0.0008" per thread you are over by .0008 x 6= .0048" - .001"=.0038 lets just say 4X.
- Although I have a C3 board for the index never put it into use. I think Russ has used it so he may comment on it.
- How linear and accurate is your Z axis?

RICH
« Last Edit: January 21, 2013, 07:28:52 PM by RICH »
Re: lathe threading pitch error
« Reply #31 on: January 21, 2013, 07:54:02 PM »
You may be getting tired of hearing this, but .... Can you verify the accuracy of you Z steps-per ?
Early on you said it was exact by referencing a move of .010". That would be difficult to verify, try a much longer move .. as long as you can accurately measure.
With a move of .010", the .0008 in .050 error would only show up as .00016 which would require quite q delicate indicator.
No problems ever with the C3 here, just that one got dirty from belt dust.
Russ
Re: lathe threading pitch error
« Reply #32 on: January 21, 2013, 07:58:36 PM »
..and be certain that the backlash is taken out by first making a short move in the "verify" direction.

Offline fast89

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Re: lathe threading pitch error
« Reply #33 on: January 22, 2013, 06:59:48 PM »
Yeah, i'm a moron. I thought my screws were .2 pitch which would be 5000 steps per inch. I have 5mm pitch screws which is 5080.01 steps per inch. Which ends up being about exactly the error i was off. Changed the steps and the first thread was perfect. The error was too small to see when jogging .010" with a .0005 indicator. Thanks to all who replied, i much appreciate it. I'll try to be a little smarter next time lol.

Offline Hood

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Re: lathe threading pitch error
« Reply #34 on: January 22, 2013, 07:02:16 PM »
Has been done many times before but you were so convincing ;D
Hood
Re: lathe threading pitch error
« Reply #35 on: January 22, 2013, 07:11:26 PM »
NOW you're cookin' with GAS ! ;D
Russ
 :)
Re: lathe threading pitch error
« Reply #36 on: January 22, 2013, 07:54:33 PM »
glad you're sorted, we'll remember this one.

Offline RICH

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Re: lathe threading pitch error
« Reply #37 on: January 23, 2013, 07:17:07 AM »
Happy you found it.
We spent many hours with Art trying to get threading fixed and don't want to revisit testing. 
Hope you now understand why we are so adamant on rpm and axis accuracy.

RICH

Offline dresda

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Re: lathe threading pitch error
« Reply #38 on: January 29, 2013, 11:03:36 PM »
I just want a copy of his modified screen for the Lathe, don't like any of the lathe screens, most machine tool controls have the same screen for mill and lathe.

Offline RICH

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Re: lathe threading pitch error
« Reply #39 on: January 30, 2013, 05:35:23 AM »
Quote
a copy of his modified screen for the Lathe

What screen are you referring to?

RICH