Boxford Model C tailstock thread

Hopefully somene will know the answer to this...

Rebuilding the tailstock on my Boxford Model C and have found that the bronze/brass nut is pretty well worn out. Looks simple enough to make a new one, it's 12 tpi, but measuring the screw thread gives me 0.482" at one end and 0.495" at the other, less worn end.

I assume it is a 1/2" BSW thread when new, but can anyone confirm this, please? Edit - Left hand thread, of course.

Thanks in advance.

Rob

Edited By Grindstone Cowboy on 15/11/2022 00:31:34

A nominal 1/2" BSW male thread would be manufactured with an OD of about .495" or even a bit less to allow for clearance on the thread tips. Otherwise the thread would bind every time the tiniest bit of fluff got in there.

Likewise the bore of the nut would be made five or so thou larger than the theoretical size before cutting the thread in it.

You can buy a new Boxford nut (listed as Boxford Tailstock Sleeve) on eBay cheaper than buying the taps to make own. But being brass, could easily enough be single-point screwcut, which would allow you to fit it snugly to your worn screw to some extent.

Thanks Hopper. I'm thinking I might re-make the screw as well, given the amount of wear on it - 13 thou over two and a half inches seems a bit excessive! it'll be a challenge learning experience for me to get it exactly right.

Would EN1A be a suitable material?

Rob

EN1A will be easyr to machine and should give a nice thread finish,but not as durable as a higher-carbon steel. But for home hobby use, running in a brass nut it should work ok.

I made some years ago a cross slide screw using en1a leaded steel, the very good finish achievable with this grade of mild steel results in a reasonable long life, a screw made in a tougher material will probably have a slightly rougher finish and will no doubt cause more wear in the nut. The nut should be made from leaded bronze,plain brass is not suitable for bearings or nuts.

If you are going to remake both you might think of going for a 10tpi or even metric convenient number though non standard thread.

Thanks for all the advice, chaps, given me a couple of things to think about (and a shopping list). And a chance to try machining a thread between centres, possibly.

Rob

Just to answer my original question, I've had it confirmed that the thread is indeed 1/2" BSW left hand from new.

Rob

The LH 1/2" BSW will be easiest to remake, try Tracey Tools for a tap. singlepionting the new leadscrew would be straightforward, and being LH you can thread away from the chuck.

6 AND 12 TPI threads are not really compatible with scale divisions, but 5, 8 and 10tpi are, fortunately a tailstock does not usually need that degree of calibration, the scale in fractions of an inch or millimeters on the quill is good enough for most work.