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10 TPI LEAD SCREW

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RichardShute:

--- Quote from: Davo J on August 09, 2010, 03:20:08 AM ---Hi,
Rdg Tools have them for £8.51, I just gave another bloke from in the US the link the other day, he ordered 2 and cost him $55 US dollars delivered.
http://www.rdgtools.co.uk/acatalog/ACME_TAPS__LEFT_HAND_.html

Dave

--- End quote ---

I used one of those RDG taps to make a feedscrew nut for my little S&B Sabel. Beware that oversize is normal for an Acme tap, I can't recall, but it's in Machinery's, a 1/2" tap is to be expected to be about 1/32nd big ie 17/32 OD. Note that the RDG one I got was a chunk bigger still, played havoc with trying to work out why the damned thing wouldn't go up the hole.
Unlike 'normal' tapping, you will not be able to use an Acme tap to 'tap' the hole, you will need to rough most of the material out with a lathe tool and use the tap just to finish it off. In my case I was using some gunmetal which is a brilliant bearing material, but sticky as hell on the tap and it was a buttock clenching job. I wouldn't be near the front of the queue to volunteer to repeat the exercise. While I was at it, I modified the design to incorporate backlash adjustment by making the nut in two halves so I can take up wear in the future.

The tradtionally quoted material for a feedscrew would have been En19 (now known as 709M40 in BS970), but I don't doubt silver steel will be very servicable, especially as you got a decent surface finish on it. Nice job.

Richard

Chazz:
A Meteroligst (sp) told me once that when hardening a shaft or any item with a large length to diameter ratio to consider nitriding to minimize distortion and promote lubrisity (sp).

Cheers,
Chazz

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