Gear Selection Question

pbiYoung

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Dec 21, 2020
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I'm unclear as to the correct order for the change gears on my lathe based on the thread chart diagram that i have attached. The lathe has a 120/127 tooth transposing idler gear.
If i want to cut 1.5mm pitch metric threads would the 35 tooth upper drive gear mesh with the 120 tooth idler and the 127 idler with the 60 tooth lower gear ? Or the the upper 35 tooth engage the 127 tooth and the 120 mesh with the lower 60 tooth? Either configuration is possible with my lathe but betting only one will cut the correct threads. Many lathes have a picture of the gears so that this is not ambiguous. Thanks to anyone that knows the answer.
MetricThread.2.jpg
 
The upper (stud) gear goes on the 127 tooth gear, the lower gear (screw) goes on the 120 tooth gear.
 
I made all the change gears for metric and DP and other leads for my 19" Regal Leblond lathe from a sheet that appeared in American Machinist Magazine, with further info from a LeBlond manual, I don't think that I have cut any metric threads since I retired, but I can!
 
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