Colchester student cross slide - what bolt threads?

I've got a round-nose Colchester Student. I'm looking to adapt a vertical slide to give me occasional milling capability. I hope to mount it to the cross-slide via the rear toolpost threads. Does anyone know what those threads are? They're round about M8 but I'm assuming Imperial. The manual itemises the bolts but doesn't say what they are. I'd be grateful for any advice.

Thanks in advance,

Dave.

Probably whitworth if not UNC as per my mk Ii

Steve

Not sure on the round head models but later Colchesters I used where UNF/UNC.

Many thanks - will look for some Whitworths and find out!

There's a list of "standard parts" at the end of the parts list for my Bantam (dated 1964) that lists all the fasteners. They are all either UNC or (a few) UNF.

Be aware that BSW has 55 degree thread angle, whereas UNC is 60 degrees. But the pitch is the same apart from the 1/2".

Murray

Happy news - the vertical slide came with four mounting bolts, which happen to match the threads in the cross-slide! I still don't know what they are, but they're 3/8" over the thread x 18tpi.

Edited By David Scothern on 11/05/2018 19:21:18

The only reference to 3/8" X 18 TPI that I can find is 3/8" NPT (National Pipe Thread) which is an American standard.

Brian

18 TPI doesn't sound right.16 or 24 perhaps but surely not 18?

In which case, I've obviously miscounted! I got 9 threads in 1/2". Definitely not 12, so let's go with 8, i.e. 16tpi.

David

might be a good idea to buy a set of thread gauges.........there are plenty of cheapo versions about.....

save a hell of a lot of time......

I've been back and found the longest of them - I'm still coming to 18tpi. I think it was my hasty measurement of diameter that was off - 5/16" rather than 3/8". 5/16x18tpi looks a bit more reasonable.

Thread gauges would be a good idea - and some basic competence with the calipers would also help!

Right, I've understood my rather basic mistake - my calipers are graduated in decimal parts of an inch, not eighths - so just over 0.3in (i.e. 5/16) rather than 3/8. Lesson learnt.

Anyway, aside from demonstrating my incompetence, and by way of rendering this thread useful for anyone searching in the future, the good people at Colchesterspares.com confirmed that the bolts are 5/16" UNC.

Thanks again to everyone for your patience and advice!