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hopefuldave:
Oh, I almost forgot - Nice Harrisson, John! Didn't mean to hijack your thread!

doubleboost:
No
Problem
carry on lol
John

hopefuldave:
Some Proper Drawings of Graham Meek's very tidy design:

http://modelengineeringwebsite.com/Meek_screwcutting_clutch.html

And a description:

http://modelengineeringwebsite.com/Screw_cutting_clutch.html

Worth a read, if only to marvel at the ingenuity :)

mattinker:

--- Quote from: hopefuldave on March 06, 2015, 06:55:26 PM ---
 http://www.model-engineer.co.uk/forums/postings.asp?th=49358&p=1
Where a lot of quite bright, practical engineers describe the mods necessary on a number of different lathes. It's worth reading, but everything in there is also in Martin Cleeve's book, if you dig a bit!

Matt, take a look at that thread - the principles apply to a lot of lathes (the Emco shares a lot of features with them) and could put you at square 3 or 4 rather than square 1?

--- End quote ---

Hopeful Dave,

Thanks for the link to the thread and the links to the drawing and description, stored away for later!

Regards, Matthew

RussellT:
I'm not sure whether this will help, but if anyone is struggling to visualise why a single point leadscrew clutch won't synchronise for screw cutting then this example helped me.

Imagine a lathe with an 8tpi leadscrew.  The half nuts can be engaged every 1/8th of an inch along it's length and the single point leadscrew clutch can be engaged every 1/8 inch of carriage travel - even if the half nuts are left closed.

 If you're trying to cut a 1.5mm thread then it will only be right when 1.5mm is an exact multiple of the 8tpi thread.  In that example every that's every 7.5 inches along the lead screw.  (60 leadscrew threads and 127 1.5 mm threads).

Russell

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