Chuck fitment to dividing head

[Matt Stevens 1Participant @mattstevens1]

So i have a Southbend 9" lathe which has a spindle thread of 1.5" x 8 TPI. I have 3 and 4 jaw chucks for it.

Recently i got a dividing head which also has theoretically the same thread. The problem is that the chucks do not screw onto the dividing head?! They go tight within a quarter turn or so….

Any ideas? It would be a pain to have to machine new backing plates and keep switching them between chucks etc.

[Matt Stevens 1Participant @mattstevens1]

[Michael GilliganParticipant @michaelgilligan61133]

I suspect that one is Whitworth thread-form and t’other is Unified.

… easy to check, at that size, with thread pitch gauges.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

It could be that the thread forms differ, or even worse, the pitch.

Reading lathes UK, it looks as if the Mandrel thread is 1.5 x 8 tpi USF, so would expect to be 60 degree thread form.

If the Dividing Head has a 1.5 x 8 tpi WHIT form (55 degree ) thread, that might account for your problem.

Male Whit form threads do not screw easily into Unified female threads, even of the same pitch; they jam!.

I would check the thread on the Dividing head with thread gauges, to establish the thread pitch and form.

Howard

[DC31kParticipant @dc31k]

If it does turn out to be as Michael suggests and if you can live with the increased stick out, make an adapter that is 1 1/2" – 8 Whit. form internally and 1 1/2" – 8 UN form externally. The chucks will then screw on to it and project a bit further from the face of the head.

Does the dividing head have an internal taper? It is possible to buy 2MT to Myford spindle nose thread adapters, so you could make something that does the same job (but nothing can poke out the back of the chuck).

[Pete RimmerParticipant @peterimmer30576]

Offer the dividing head spindle thread up to the South bend spindle thread. If the pitch is the same then the threadform must be different. Get a 1.5" – 8 TPI UNS die and run it down the thread on the dividing head, then your chucks will fit, and so will any Whitworth ones.

[Dave HalfordParticipant @davehalford22513]

Posted by Matt Stevens 1 on 18/01/2021 17:58:08:

So i have a Southbend 9" lathe which has a spindle thread of 1.5" x 8 TPI. I have 3 and 4 jaw chucks for it.

Recently i got a dividing head which also has theoretically the same thread. The problem is that the chucks do not screw onto the dividing head?! They go tight within a quarter turn or so….

Any ideas? It would be a pain to have to machine new backing plates and keep switching them between chucks etc.

I've heard that one too. My Rockwell Delta 10" takes Boxford thread backplates, but not my BS0 dividing head backplate

[Matt Stevens 1Participant @mattstevens1]

Hi All,

I will check the threads against one another per your suggestion…thanks.

I suspect ordering a 1.5" 8TPI UNS die will be pretty expensive for a one time use, assuming i can find one. ANyway, i will get to the group with my findings.

P.S. It does have an MT2 taper.

[Pete RimmerParticipant @peterimmer30576]

You could remove the spindle from the dividing head and single-point the thread, so long as it's not hardened.

[Dave HalfordParticipant @davehalford22513]

Are we sure this isn't the problem ?

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