My Harrison lathe has a qc gearbox which will cut metric or inch threads. The leadscrew is 4 TPI. Looking at the qc gearbox parts assembly, I do not see any multiple gear ratios which would give the 127 factor needed for "perfect" metric off the inch leadscrew. Putting a digital scale on the carriage and measuring over 20, 30 or 40 threads, there is ZERO error.

Does anyone know what sort of gear combinations the Brits used in these things to get this (perfect??) conversion. I can see where a multiple ratio scheme might work where one ratio is on the low side but the next is on the high side ... but perfect cancellation ??

Paging Marv Klotz ?

Den

Does anyone know what sort of gear combinations the Brits used in these things to get this (perfect??) conversion. I can see where a multiple ratio scheme might work where one ratio is on the low side but the next is on the high side ... but perfect cancellation ??

Paging Marv Klotz ?

Den

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