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Not seen it done that way before, most people turn the main shaft first and then just hold by that in a keats plate or similar homemade jig to turn the pin/form pin hole, far easier than working between two webs an no need to drill pairs of ctrs at each end of the bar.J
part of the reason for doing one of these tiddlers is to learn if and why machining them might be different than bigger engines and if there is any advantages or disadvantages of those techniques.
JoPlease use a either a properly ground HSS tool or a proper threading insert with the correct anvil to get the helix angle correct in your threading endeavours That tool shown may be the correct angle but a threading tool it is not
set both dials to zero move the carnage to the left off the work ,
The other thing that discourages me is the confusion of change wheels, gear boxes and leadscrews. The Prazimat/Cowells have metric lead screws and no leadscrew indicator and talk about using the complete reversal method. The Myford and the Colchester have imperial lead screws and have indicators.Jo