Boxford Screwcutting

I have a Boxford AUD with screwcutting box. It's not often that I do screwcutting and so have hit a snag.

I'm making a backplate so need to cut an internal 1 1/2 X 8TPI thread, which I've done before but many years ago.

I have read the book 'Know Your Lathe' and it says to put a 20T gear on the stud shaft which I have done, there is an idler gear which is of no consequence and then there is a gear on the gearbox input which is called 'the screw gear' but there is no mention (that I could see) of the number of teeth.

Now, there are two gears on my screw gear shaft instead of a gear and a spacer and so I don't know which gear should be in the train.

Any help gratefully received.

Brian

If your lathe is metric the screw gear is 50T. If it is imperial it's 40T. I'm guessing your lathe is imperial and you probably have both 40T and the 50T. The 50T can be swapped with the 20T idler to get the full range of standard threads.

Edited By Gavlar on 29/01/2021 19:08:17

Edited By Gavlar on 29/01/2021 19:10:29

Many thanks Gavlar, I'll check it out in the morning.

Brian

Further to the screwcutting thread (no pun intended!) The tools I will be using as shown in the picture, were to be thrown away when the local Dormer factory closed a few years ago. Fortunately, a friend worked there and rescued them from the skip.

These were used to produce taps and dies in the days before carbide tips came along. The cutting tools are made from tool steel with a common 1/4" shank to fit a holder and are for every conceivable thread form including light bulb and screw bottle top.

There are also boxes of chasers to finish the threads, one of which for MM is plainly visible.

Brian

Sorry, but the info. above is incorrect. For 8 tpi on an imperial lathe, the stud gear is 20 T, The screw gear is 56 T. The recommended idler is 80 T.Any small gear can be used as a spacer on the screw.

To get the coarse threads, 7 tpi and less, the screw gear is 40 T.

These arrangements are show as a diagram on page 65 of my copy of "Know Your Lathe".

Yes, you are right, sorry, trying to do it from memory!

Thanks for the clarification Clive. I have a copy of 'Know your Lathe' but, of course, the diagram on my copy is indistinct!

Brian

Just to let you know, I've cut a 1 1/8" x 8tpi thread to make a backplate for an ER32 collet holder and used the gears mentioned in the post from Clive.

Brian