With lathes that can only drive the tool towards the headstock the procedure can be described as follows: advance the tool, watch the thread indicator and engage half nuts and make a cut. At the end of the cut disengage the half nuts, retract the tool, wind the carriage manually back to the start point, advance the tool again to a slightly deeper cutting depth and repeat the sequence. It is clear from this description that this is a complicated sequence and forgetting to retract the tool or failing to engage the half nuts at the exact point indicated by the thread indicator has ruined many a thread.
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