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Hi Chaps, I’m after some help identifying a thread on a barrel jacket from the Browning 303 Mk2. The thread appears to be that of a 32 tpi 55 deg Whitworth thread 5/32 bolt but the jacket is 1.562” in diameter. Would anyone have an idea? Perhaps carried over from the American ANM2 .30 cal?
I would imagine that the thread would simply be a thread on a diameter BP. In this case, exactly as you say, a 55 degree (but I suspect it'll be 60 degree somehow...) 32TPI thread on the 1.56 dia.
If it was me I'd machine the thread onto a bar of mild steel and see how you go.
The 1.562" is a very odd diameter. But less odd if you think 1"17/32, which is 1.5625".
And 32 tpi threading gear? I have quite a bit. Admittedly not in that diameter, but 32 tpi Whitworth-form thread on various diameters is common enough for engineering piping applications that it does not surprise me. Just get yourself a Coventry die-head and the cutter inserts, and away you go!
Thanks Peter, a 60 deg Metric thread pitch fits too but I assumed being vintage British that it was more likely Whitworth. And you know what they say about assumption.... I also need to learn how to cut threads on the lathe rather than using a die on the lathe and turning the chuck by hand (I have been watching Utube vids to get the idea)
Thanks for the reply too Patrick, I think 1.562" is 1 and 9/16 though. I'm assuming (again) that the diameter of the jacket originates from the US Colt ANM2 .30 that the .303 was based on, I can't be sure though as I don't know anyone who has one.
I can see me taking my part finished replacement to a more competent engineer than myself. At least I can take it and not sound a complete idiot when I ask them to cut a thread on it.
Thanks, Chaps.
Quote:
Originally Posted by Brit plumber
Oops ! You're right :o
You shuld be able to cut that thread on a little Myford BP. Is yours a lever change gearbox or old cog-change gearbox? Either way, once you have done the simple maths/ratios it should be a simple matter. Just practice on a few offcuts from the fitter/turners shop. Especially easy if you are cutting an external thread
BP, I can give you a few pointers regarding threading on a lathe, one thing you need is the gauge below, cheap as chips and saves a lot of tears, used mainly for lining up the tool so its square to the job.Quote:
Originally Posted by Brit plumber
https://www.milsurps.com/images/impo...DSCF3301-1.jpg
I've got a good idea BP and Big Duke......... Next time you're up in that neck of the woods BP, you both come from/live in that part of the world, maybe you could join forces with Big Boy for a few hours on his machine and just run through a few valuable pointers.
Thanks guys, I may just have to have a go at this my self, the youtube vids make it look harder than I think it actually is. I have the kit, I just need to make sure that I can get the tube in the lathe bed. As its a slight cone, I don't think it will go in the chuck unless someone has another idea.
Big Duke, am I right in thinking your up Carlisle way?
Post a photo of the tube, marking where the thread should be cut, and I can advise you how to hold it and do the job.Quote:
Originally Posted by Brit plumber
Hi Patrick, Said cone is currently a tube, I need to make a mandrel and force the tube over to make the cone. The end result should look like this...I hope.
https://www.milsurps.com/images/impo...12_zps6b-1.jpg
The mandrel should be made somewhat longer than the workpiece, with center-drilled recesses at both ends, so that the workpiece can be turned and/or threaded while it is mounted on the mandrel, which itself is either mounted between centers, and driven by that almost-forgotten device, a lathe dog, or with the one end of the mandrel in the chuck and the tailstock end running on a center.
Of course, it would be easier to cut the thread before creating the taper! The trouble with tubes is that holding them in a 3-jaw chuck is a recipe for disaster for anything but very light facing cuts. A 3-jaw squeezes the tube into a 3-lobed cross-section and/or presses grooves into the tube, so the usual method is to use a collet, and the difficulty is typically to find a collet that has an adequate through-bore to take the tube body, leaving just the portion to be threaded outside the chuck.
If you have the patience, but no suitable collet attachment, then one solution is to turn up a special "one-off" collet. Fix a piece of suitable brass bar in the chuck, face it off, bore out to the outside diameter of the tube as closely as you can, so that the tube just slides in if it is greased. File a mark on the faced-off end of what is now a brass bush to mark the orientation of the tube with respect to the chuck jaws. Marking with a pen is no good - been there, done that - the mark is bound to rub off in handling!
Remove the bush and cut 3 equally spaced longitudinal slits at one end of the bush, about 3/4 of the length. Repeat at the other end, with a 60 degree shift, so that the slits from the other end lie between the first set.
You now have a hand-made "concertina" collet that can be reinserted in the chuck (observe the jaw orientation mark!) and squeezed up ever so slightly to grip the tube perfectly, without causing any distortion. You can now turn the thread on the exposed portion.
And if you think this sounds like theory, it most definitely is not. I have used such a device to remove the bell-mouthing from the last millimetres of a black-powder barrel. Very, very slow, but it worked!