Where in the country are you Simon ?

I have a Boxford spindle nose tap I would be happy to run through your backplate if we are close enough to meet up – I live In West Yorkshire.

Nigel B.

On 16 December 2023 at 10:47 Simon Ricketts Said:

…does anyone have any other suggestions given my lack of equipment.

What equipment do you have?

Let us say you only have the backplate.

Buy a soft Morse taper arbor that suits the spindle taper. Turn down a shoulder on it. Drill and tap it for a securing bolt.

Cut a circle of plywood and drill a hole in it to suit the diameter of the shoulder of the arbor. Bolt wood and metal together using some large metal washers sandwiching the plywood.

Mount in spindle and use a pen to draw a circle on it the same diameter as the backplate. Fix backplate to plywood concentric with the circle you have drawn. Woodscrews and plywood cleats will do for this.

Set lathe to cut 3.175mm pitch, put screwcutting tool into toolpost and chase out thread.

The likely point of failure of this setup is for the plywood to slip rotationally on the arbor so give it a good tug with your hand to see how secure the connection is and reinforce (glue, weld, pin) if necessary.

On 16 December 2023 at 14:27 Simon Ricketts Said:

…first time I’ve done internal thread cutting before…

Am I right in saying I’ll need a 60 degree tool angle for this thread?

A Boxford owner will be along soon but I am under the impression that Boxfords used a Whitworth (55 degree) thread form. The US South Bend, to which the Boxford owed many design features had a 60 degree thread form.

You are not really thread cutting, more thread chasing. Which means you need to pick up the existing thread. It is actually easier to pick up an internal thread than an outside thread.

With the halfnuts engaged (and as you have a metric lathe, they will need to remain so throughout the process), leave the tool slightly loose in its holder and slide it forwards and backwards until it fits the thread groove. Then tighten the tool in its holder. Blue up the internal thread* and take a scratch pass as the first pass. Examine the blued up thread after this pass and you can verify that the tool is correctly aligned and adjust if not. For what you are doing, I would be turning the spindle by hand.

*you could also blue up the tool and examine that after the first pass.

I understand that the Boxford thread is 55 deg. You face a problem with setting up to cut 8 tpi on your metric machine.

Boxford list 3.0mm and 3.5mm pitch as standard set-ups, neither are near enough for your need of 3.175mm. If you happen to have a Boxford 135-127T gear then you’re home and dry, otherwise you may get near by juggling the standard gears, but the gearbox complicates calculations.

If I may suggest, paying postage to take up Nigel B’s kind offer might be your best course of action.

I bought a Boxford faceplate for my South Bend 9″, all other Boxford parts fit it but I found a similar problem with it not screwing on all the way, I found my lathe dated to 1939 and from 1940 on they made the slight alteration to the thread  at 55 degrees as mentioned above. So I never did anything to fix the faceplate

I hesitate to raise this, but when you screw it on and it jams up after half a turn, is the plain register on the backplate still clear of the register on the spindle?

If the two are already in contact at this point, could it be a tight register on the backplate rather than a problem with the threads?

Simon –

I’m retired so most days are fine. Parking near my home can be a bit of a doo-dah at weekends and in the evenings, though.

I’m near Weymouth. PM me with ‘phone number or e-post address.

I’d suggested my visiting you so we can actually test the thread there and then, but if it’s just a matter of running a tap through to ease the thread, as RDG advised, it ought not matter.

O.K. you seem to be fixed up now but for future reference you might find the little change wheel calculator NthreadP useful for cutting imperial threads without a 127 wheel.

http://www.lathes.co.uk/latheparts/page14.html

Russell