pick-o-matic metric thread?

I have an Atlas 10 in. lathe with the Pick-o-Matic gear change setup. There is a wheel on the inside cover that has a listing for the various
feed rates and TPI available. My problem is that I now need to do some metric threads, 1.0 and 1.25 mm pitch. Does any one know if this possible on this lathe?
The lathe dates from 1945 or so and has worked well so far. But perhaps obsolescence has overtaken it.
Thanks Dave Scott
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I don't know this lathe. But if it has a wheel with 127 teeth, chances are very high. If not, she can't.
HTH, Nick
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Dave Check into the Atlas_Craftsman Yahoo group. Very active group, 3500 members, lots of posts. Search the archives, and the files section, as the question comes up regularly. In short, you can do it with the right change gears.
- - Rex Burkheimer
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On 24 May 2005 21:29:34 -0700, " snipped-for-privacy@aol.com"

This question comes up every so often here. To generate an absolutely correct metric thread [assuming a perfect inch lead screw] a 127-tooth change wheel is indeed required. The problem is this is a large gear [relative to the other change gears] and may not fit.
Because the thread engagement of most lathe parts is only two or three diameters, a thread that is "close enough" is all that is required.
The ideal metric/inch ratio is 127:100 or 1.27000
Other smaller gears can be combined to give very close approximations of the ideal ratio.
For example
47/37 = 1.27027023 or +0.02128% lead
80/63 = 1.2698127 or -0.012498% lead
There are of course other combinations.
An additional benefit is that generation of a 127 tooth gear requires differential/compound indexing which is beyond the capabilities of most inexpensive dividing heads, while 47,37,and 63T gears can be generated with the typical home shop equipment, and you are likely to already have an 80T gear.
Remember if you are using a metric/inch change gear, you *MUST* keep the half nut engaged as the thread indicator does not work with these odd thread fractions. A spindle crank can be a lifesaver if you need to thread to a shoulder.
GmcD
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Thanks for the info. I'll try with the 47/37 combination and see if it works with the gears I have. A 127 tooth gear would be too big for the space available anyway. Dave Scott
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