Boxford spindle nose specs

This topic has 8 replies, 7 voices, and was last updated 30 April 2026 at 09:04 by Oldiron.

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19 April 2026 at 22:03 #845116
Paul Relf-Davies
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@paulrelf-davies37806
I hope someone here can help me out. I have a pre-war (1933) Colchester Bantam lathe. It’s spindle nose has an inch and a half 8tpi thread, with a 1.562″ diameter registration surface, about 3/4 of an inch long.

I’m looking for a chuck backing plate for it and I believe Boxford lathes use a similar inch and a half x 8tpi thread.

Would a backing plate for a Boxford lathe (such as from RDG tools) successfully fit and properly register on my ancient Bantam…(or be modified to do so)?

I appreciate that the thread would probably need chasing as mine will be a 55° thread and I believe the Boxford used a 60° thread. I’m also not averse to machining the register surface, if necessary.

Thanks

Paul
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19 April 2026 at 22:07 #845121
Grindstone Cowboy
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@grindstonecowboy
Well, the good news is, that apart from the very early ones, Boxfords (at least the South Bend clones) used a 55 degree thread. I have a dimensioned drawing of the spindle nose somewhere, I’ll post it when I find it.

Rob
19 April 2026 at 22:25 #845123
Grindstone Cowboy
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@grindstonecowboy
19 April 2026 at 23:30 #845126
Bazyle
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@bazyle
SouthBend are UNC 60 degree and BoxFord are Whitworth 55 degree. If you get a premade backplate and it is a little tight give it a good clean and also try it on backwards – oddly that freed one up for me (but 20 years ago so not a reflection on current stock).
20 April 2026 at 07:54 #845146
Paul Relf-Davies
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@paulrelf-davies37806
Marvellous! Many thanks, both. I’ll order a plant from RDG and see how it goes. It’ll be good to get my 97yr old machine back to making chips.

Paul
29 April 2026 at 20:16 #846259
martian
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@martian
I bought a backplate recently from RDG, just been machining it this evening for use on my Mk 3 Boxford.
They are 1 1/2 x 8 BSF, so 55 deg. It was a bit tight on the spindle but after running a tap through it and it fits nicely.
30 April 2026 at 06:32 #846312
Speedy Builder5
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@speedybuilder5
Is my memory playing tricks – I had a Southbend and replaced it with a Boxford. I kept the faceplate and the 4 jaw chuck and they fitted the Boxford without changing the thread form.

Ie the 60degree threaded plates fit the 55 degree spindle nose – is that possible or is my memory playing tricks ?

Bob
30 April 2026 at 07:28 #846316
DC31k
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@dc31k
On 30 April 2026 at 06:32 Speedy Builder5 Said:

Ie the 60degree threaded plates fit the 55 degree spindle nose

Draw a picture of a theoretically exact male Whitworth form thread.

Draw a picture of a theoreticaly exact female UN form thread.

Overlay the two and appreciate the issue at a theoretically exact level.

Adjust one or both* until there is no interference and an amount of clearance that looks right to you.

Assess whether the new dimensions fit within one of the standard thread classes for that thread form.

Whitworth and UN can be made to interchange if the tolerances are large enough. Commercial nuts and bolts do so by observation, so their tolerance is an upper limit to this calculation. Your calculation above would give the lower limit to this.

* Measuring your spindle with proper thread wires to determine its actual pitch diameter would give a reference for your own situation.
30 April 2026 at 09:04 #846327
Oldiron
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@oldiron
Very early Boxford’s used a 60 deg thread but later ones used 55 deg so you should be OK. I have used several RDG back plates without issue.
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