19 TPI

It must be on this site some where, but how do I cut a 19TPI thread. The Norton box gives 18 and 20, but annoyingly not 19 for 3/8 BSP threads.
BobH

Not going to help you, but on my Norton box it sits right between 18 and 20

Play about with the gears between the spindle and gearbox input, don't really know what you have on te Boxford so can't help much more than that

You'll either have to tweak the gearbox drive train in the ratio 18/19, or 20/19. Alternatively, if you're near Cambridge come and borrow my lathe.

Andrew

I suppose the Boxford is very similar to a South Bend lathe I used to own. When faced with cutting 19 TPI I used 20 TPI cut a bit loose as most pipe fittings are short I got away with it, plus I have dies up to 1/2" BSP to correct things. My newer lathe does do 19 TPI.

If your lathe has 28 tpi on the gearbox easiest way is to double the size of the stud gear or halve the size of the gearbox input gear. For a SouthBend 9" I think doubling the stud (input) gear size is the recommended way as the gear required is one of the standard set for a non-gearbox version. Also part of the conversion set for metric threads.

Clive.

Clive would that not give 14tpi.

Might works if the box has an unusual 38tpi option

Edited By JasonB on 10/07/2017 15:35:37

Um, 38 tpi?

For a Boxford, if you happen to have either a 54 or a 60t change-wheel, replacing the 56t input gear will give 19.28tpi by setting to 20 or 18 tpi on the 'box.

That's been adequate for me for short lengths of thread.

Someone is selling 38t Boxford change-wheels, made of plastic, on Ebay, that would be a way to be spot-on.

Ooops. Need new glasses. John and Jason are right. Sorry I mis-read my reference.

Clive Brown has the answer. 38 tooth gear on gearbox input with standard 20 tooth stud gear with 28 TPI setting on the gearbox gives 19 tpi.

Clive

Thanks Clive and others, Yes, I have a 54 and a 60, so 19.28 tip would be good enough. Thanks for the offer Andrew, could you pick me up from out local airport - SW France ? Joking apart, thanks everyone.
BobH

Hello Speedy,

​Stud gear 20, screw gear 38 and gearbox set for 28tpi will give you 19tpi exactly

Regards
​Brian

Thanks Brian - I just need a 38 Tooth cog !
Bob

Make yourself a 19t by filing the teeth. Changewheels do not need to be very precise for making fixings, only when you are making a new leadscrew for another lathe.

Hello again Bob,

​I like a challenge! I've worked out some more gearings for you without knowing really what you have in the way of change wheels. You've already mentioned a 54 and 60 and I assume you have the standard 56 wheel

For 54 wheel as screw gear, with 16 as stud gear and 16tpi set in the gearbox you get 0.05185 inch pitch [19.29tpi]

For 56 wheel, 24 as stud gear and 23tpi on gearbox you get 0.05219 inch pitch [19.16]
and for 25 stud gear and 24tpi on gearbox you get 0.05208 inch pitch [19.2 tpi]

​For 60 as screw gear, 36 as stud gear and 32tpi on gearbox you get0.05249 inch pitch [19.05tpi]

Some options for you

​Regards Brian