Lathe acme screw threads

  1. spencer 427

    spencer 427 Member

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    Evening guys.
    Has anyone of you chaps made cross slide lead screws with acme threads.
     
  2. Pete.

    Pete. Member

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    Yep, it's not difficult. I made one with a 2-start thread came out nice.
     
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  3. Richard.

    Richard. Member

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    I remember seeing the tool you made for that twin start thread. Was impressive stuff.
     
  4. spencer 427

    spencer 427 Member

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    Ok. I might have a job for someone who would be able to make me one. I will explain. After close inspection and a removal of the cross slide gear cover I noticed that a cog was missing and the end of the cross slide shaft has been broke off. The cross slide works but I want it to work as was from factory. I am currently sourcing information on the size of the missing cog. 20171114_191849.jpg 20171114_191841.jpg 20171114_191831.jpg
     
  5. Spark plug

    Spark plug Member

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    You should be able to work out the size of the missing gear, first by working out the DP (pitch) of the existing gear then you can calculate the number of teeth require, from the existing gear and the spaceing of the shafts.
     
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  6. Pete.

    Pete. Member

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    Looking at the pic on the lathes website it seems like it had a star wheel which most likely had a spring-loaded sliding gear on the shaft. Looks like all that's broken is the thread for the star wheel. Drill and tap the cross-slide for a new thread.

    EDIT: actually I bet it was a star wheel and friction clutch.

    starwheel.JPG
     
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  7. spencer 427

    spencer 427 Member

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    The operating leaver and clutch all works. Just the missing star wheel / cog. 20171114_191849.jpg
     
  8. Pete.

    Pete. Member

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    Best I can tell the operating lever only works the sliding feed. Surfacing feed looks like it's engaged by tightening the star wheel. Lots of lathes have this but it's usually on the front of the apron.
     
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  9. spencer 427

    spencer 427 Member

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    Yes. The leaver just engages the sliding feed.
     
  10. spencer 427

    spencer 427 Member

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    Yes I see what mean now
     
  11. spencer 427

    spencer 427 Member

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    Just found this picture Pete. Think your right. img9.jpg
     
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  12. Pete.

    Pete. Member

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    In that case just make a star wheel, find a gear and use two bronze shims for a clutch, one pressed on the shaft and one loose under the wheel. Easy fix.
     
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  13. spencer 427

    spencer 427 Member

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    Yes. Got to get reading and suss it out so I understand it.
     
  14. Pete.

    Pete. Member

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    Work out the DP of your big drive gear (tooth count + 2 / diameter in inches). Get a piece of card and drill a hole in it so that it fits on the shaft and mark the card at the bottom of one of the teeth in the big gear. Now turn the card 180 and mark again. the two marks will be the diameter of the gear apart (ignoring clearances). From that you do (diameter x DP) minus 2 to get your tooth count for the small gear. Now you know the DP and the tooth count all you do is find a gear and bush the middle with bronze or cast iron to fit the shaft.
     
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  15. spencer 427

    spencer 427 Member

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    Got ya Pete. Awesome. Thanks for the information mate. Appreciated. Will do that tomorrow.
     
  16. Pete.

    Pete. Member

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    Just had a thought you could take a pen and stick it in the bottom of a tooth on the big gear then spin the card to draw a circle :)
     
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  17. Hood

    Hood Forum Supporter

    Am I missing something, why not just measure the distance from centre of shaft to bottom of tooth then double?
     
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  18. Pete.

    Pete. Member

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    Could do that aye. Kinda tricky with the shaft broken and poking out beyond the gear but I suppose you could go bottom of tooth to shaft Od then add the radius. Many ways to skin a cat etc. For getting the tooth count it need not be super accurate.
     
  19. spencer 427

    spencer 427 Member

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    Ok. Been doing some research so to get a better understanding. gear-termslessonrev3-4-638.jpg Sprocket16.png
     
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