Okay, it is checked – and I think I can see why you might have been having some difficulty with this, if it’s anything like mine…

 

Yes, the drawbar is clearly meant to have a 1/2″ Whitworth thread, and for all I know the thread cut into the M3 taper is correct, although since I can’t find my 1/2″ Whit tap to check this, I haven’t yet. But the thread cut onto the drawbar itself isn’t quite 12 tpi – it’s actually about 12.2 tpi, and that’s enough to bind the thread after a few turns, assuming that it’s cut correctly. But there’s the rub; it isn’t cut correctly at all – it’s a pretty loose fit, and after about an inch it’s slightly malformed anyway. The thread OD measures 0.495″, and whilst that’s only slightly undersize, I’d say from looking at it and running a thread chaser along it that it’s cut pretty deeply, and that’s why it goes in sufficiently. With a bit of effort at the end, I can just get it to screw in for about an inch by hand, which is how far in it’s tapped. I think that it should have gone in a lot more easily.

 

The overall dimensions of the drawbar are that the shaft is 15″ long, and the last 1.5″ of this are threaded. It has a 7/16″ Whit head on the end, and yes I’m pretty convinced that this is original.

Bit unlikely that they’d really be UNC – hardly anybody here was using UNC in the early 50’s, which is when my TS was built. I still think that it’s a badly fitting Whitworth, although I can see why a 1/2″ UNC would sort-of fit.

 

Since mine was clearly, erm, ‘mullered’ somewhat, I took a careful look at it, and then ran a 1/2″ UNC die over it anyway. It took off about as much metal as I would have expected to have come from converting a 55(ish) degree pitch to a 60… and it still jammed in the arbour. So I ran a tap down that, and now it’s slightly on the loose side. This doesn’t particularly bother me for two reasons; the drawbar doesn’t exactly need to be done up ridiculously tightly, and anyway it would be very easy to make a new one with a proper 1/2″ UNC thread, which will work much better – I tried an accurately cut thread in the arbour, and that’s fine. I will probably make a new drawbar anyway, because the other thing I’ve noticed about the old one is that it’s very slightly bent, and is in far worse condition than the rest of the arbour, which is in very good condition indeed.

 

But what size arbour have you got for it to have a 1″ UNC at the other end? Mine’s a 1″ arbour, and the thread at the other end is considerably smaller than that – the thread OD is only 3/4″, and it’s 12 tpi, and that makes it very clearly a 3/4″ BSF, because nothing else at that size uses that pitch.

The 30int arbours are definitely later ones, and if Boldminer’s is also a 30int, that might explain the difference in overall length of the drawbar. You have to be a tad careful with this 30int thing though, because the 3MT arbour also has a locking cutout in the end of it that makes it look suspiciously similar at first glance. I don’t really know why they changed this, because to all intents and purposes, a 3MT female with a locking slot cut across the end and 30int perform in pretty much the same way.

 

If I get time later, I’ll post a picture of my arbour, so you can compare.

Hi Ian,

 

That’s either a coincidence or plagiarism,  I’ve already pointed that out on another thread.

 

 

 

Hi Steve,

 

I’m not sure about your treatise on the  American spelling of arbour, according to Wikipedia a mandrel is:

“in American English also called an arbor (my emphasis),  is either an object used to shape machined work; a tool component that grips or clamps materials to be machined; or a tool component that can be used to grip other moving tool components.”

 

best regards

 

Terry

 

 

 ‘Two nations divided by a common language’

 

 

Hi Steve

School seen to be never out LOL…

I had a problem with another unknown thread, Taking the shaft to a nut and bolt supplier that is his name worth idenified the thread and order me the correct nuts and threaded section.

Eddie