Help Identifying a chuck back plate

[Mark Davison 1Participant @markdavison1]

I have a threaded back plate for lathe that is looking for a new home. It came on a 6″ Pratt 4 jaw independent chuck that I bought off eBay a few years ago.

It appears to be a 2″ x 4 TPI 60 degree thread. It could be 6mm, it is hard to get my short thread gauge in and to see at the same time.

The plain register is 2-1/16″ (if it’s imperial).

Any ideas as to what lathe this make/model lathe it would fit?

[Nigel Graham 2Participant @nigelgraham2]

If it narrows things down a bit –

 

60º suggests metric or American thread.

4tpi X 60º suggests American (Unified) thread although the standard 2″ UNC is of 4.5tpi.

2.1/16″ = 52.39 mm, which does not seem a logical metric size. Even if allowing for wear, 53mm is not very logical either; but it would have a metric thread anyway.

So the original lathe could be of US manufacture.

[DC31kParticipant @dc31k]

[Michael GilliganParticipant @michaelgilligan61133]

As I have stated repeatedly … it is a simple matter to take a wax impression from a thread, and [at the scale being discussed] it  should be a trivial task to distinguish between the Whitworth and Unified thread-forms

.

.

MichaelG.i

[JasonBModerator @jasonb]

OP says he is using a thread gauge and at that sort of pitch the gauge should easily show it is 60deg not 55.

[Michael GilliganParticipant @michaelgilligan61133]

Agreed … but he specifically states:

it is hard to get my short thread gauge in and to see at the same time.

MichaelG.

[Mark Davison 1Participant @markdavison1]

I tried both 60 and 55 degree thread gauges.  It is definitely not 55.  I could see enough of the first thread to be sure but it is hard to get a good view of the fit with the 3rd and 4th threads to see a subtle difference between 4TPI imperial 6mm metric.

[Michael GilliganParticipant @michaelgilligan61133]

Then Nigel’s logic seems sound to me

It is most likely for  an American spec. lathe.

MichaelG.

[old martParticipant @oldmart]

There is a possibility that it is not from a lathe, some dividing heads have threads.

I will ask about it on the Home Shop Machinist forum over the other side of the pond.

[Andrew CrowParticipant @andrewcrow91475]

[Mark Davison 1Participant @markdavison1]

Andrew, if it fits you can.have it. PM me.

[cedric 1Participant @cedric]

[Andrew CrowParticipant @andrewcrow91475]

<p style=”text-align: left;”>Hello Mark, I think “old mart” has probably got the right idea, although not the same as my Brown & Sharp, having just measured it as 2.5 diameter × 4.5 tpi and almost certainly of American National form.</p>
Because of the awkwardness of it,  I made an adaptor to suit the chucks and face plate I used on my old Colchester Student (also with an adaptor to suit a D1 spindle taper) so I could transfer between the two  without disturbing the job.

[Mark Davison 1Participant @markdavison1]

Based on this thread

KERRY TYPE A.G. LATHE

by

@steveambler1

It sounds like it may fit a Kerry A.G. lathe.

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