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Threading odd pitches in the lathe

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benmychree

John York
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#1
When faced with cutting a thread pitch that is not on the lathe's chart, the thread may be cut by the use of change gears; a good example is 27 threads for 1/8" pipe thread, which very few lathes will cut. You first select a position on the quick change box that is close to the desired pitch, say 30 TPI; place a 30 tooth change gear on the shaft driven by the lathe spindle and tumbler gears, to mesh with the large idler gear, then place a 27 tooth gear on the input shaft to the quick change box, or other gears that may give the same ratio, like 60 and 54 teeth (and still set the QC to 30). I have done this several times on my 19" Regal Leblond. I made a set of change gears to cut most all metric leads, special "imperial" pitches and diametral pitch leads and long leads.
 

benmychree

John York
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#2
Here is a picture of all the special change gears described in my original post; the metric transposing 120 and 127 gears stay on the lathe. This box full weighs about 70 lbs; most of them were cut on my automatic gear cutter, for which I had to make a whole set of change gears in order to use the machine; they were cut on my milling machine, which takes 14P gears, the lathe takes 12P. The 127 tooth change gear was divided and cut by differential indexing on a universal dividing head.
 

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magicniner

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#3
When I bought my lathe I chose the one with change gears rather than a gearbox knowing that I would be cutting a wide range of Imperial, Metric and Odd-Ball threads and that a gearbox can be a limitation ;-)
 

benmychree

John York
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#4
When I bought my lathe I chose the one with change gears rather than a gearbox knowing that I would be cutting a wide range of Imperial, Metric and Odd-Ball threads and that a gearbox can be a limitation ;-)
It would depend on the lathe, whether or not the QC box is a hindrance; on my Regal, it is not a hindrence to setting change gears for special threads; however on the 14"Monarch that I sold with my business it was a near impossibility due to its construction.
 
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