Subject: Pratt & Whitney Lathe

From: [email-masked] (Henry Kroker)
Date: 30 Dec 1994 02:10:07 GMT

I recently purchased a really old Pratt & Whitney lathe.
I have not located any model info on it but most parts have "22"
stamped on them.

It came with a taper attachment, has an 11 inch swing, and runs 36"
between centers.

The question I have concerns a box of "backoff cams"
They consist of circular cams with one and four lobes of varying rise.

Can anyone hazard a guess as to what these could have been meant for?

Since gear changes on this machine are required for threading operations,
 and I don't have manuals I have been trying to derive some equations based 
on test samples, but this does not appear to be accuarate enough. 
(the ratio in the carriage does not appear to be what I guessed at)

Does anyone Know a proceedure for determining the correct gear ratios for
threading operations?

The last question concerns availability/ interchangeability of spare
parts? a manual? (a long shot)

Thanks

Ps this has got to be the best news group out there. I've enjoyed reading
for a long time.

henry

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From: [email-masked] (Mike Rehmus)
Date: 30 Dec 1994 19:02:56 GMT

In <[email-masked]> [email-masked] (Henry Kroker) 

>Ps this has got to be the best news group out there. I've enjoyed 
reading

Measxure/count everything in the gear train and then read the section in 
Machinery's Handbook on treading / gear selection.  It has all the 
answers if you can just wade through all the detail.

Backoff cams sound like a device to retract the toolbit when moving back 
to the beginning of a cut.  Seems like I saw someting about this in the 
book series on mechanisms.

Best,
Mike

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From: [email-masked] (Ron Ginger)
Date: Fri, 30 Dec 1994 14:49:44

In article <[email-masked]> [email-masked] (Henry Kroker) writes:
>From: [email-masked] (Henry Kroker)
>Subject: Pratt & Whitney Lathe
>Date: 30 Dec 1994 02:10:07 GMT
>Keywords: lathe

>I have not located any model info on it but most parts have "22"

..........

>Can anyone hazard a guess as to what these could have been meant for?

Ive seen a cam arrangement used to back off cutters. That is, to make cutters 
that are not round, but lobed. I think there was an article in Model Engineer 
a few years ago about making an adapter and backoff cams.

A form of gear cutter can be made by turning a four sided shape, kind of a 
square with arcs for its sides- by making 4 eccentric cuts.

Ron Ginger
my signature is http://www.ultranet.com/~ginger

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From: [email-masked] (ChrisB1981)
Date: 30 Dec 1994 14:58:43 -0500

You should be able to find the TPI on the leadscrew without too much
trouble.  The rest is just math.  So if the leadscrew is 10 tpi and the
mandrel is geared to it on a 1-1 basis, it will cut a screw of 10 tpi, if
the mandrel is rotating twice as fast, it will cut 20 tpi etc.  
"The Amateur's Lathe" by L. H. Sparey,  has a short, clear explanation of
this. 
This is a British book, published by Argus, I received my copy from
Campbell Tools.  No doubt other vendors will have it also.

Reg Barron