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.
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