The lead screw of a lathe is used to advance the carriage of the lathe in time with the rotation of the spindle. It is used to make threads by having different gearing between the spindle and the drive for the lead screw.
Advantages & Disadvantage:
Some lathes also use the lead screw for fine feed, so you don’t have to sit there and crank the handle. This has one advantage, and a couple of disadvantages.
Advantage – Cheaper to make.
Disadvantages – the lead screw, and the half nuts take extra wear and the fact that SOME lathes that have separate feed screws and lead screws allow you to set the rates separately, and almost ALL have the feed screw running much more slowly, so even if you have the lathe set for a fairly coarse thread, the feed screw is in a “somewhat useful” range.
How to use?
Lead screw in the lathe is used while cutting threads on a job. For thread cutting the feed of the cutting tool should be in correspondence with the rotational speed (rpm) of chuck/workpiece which is different for different threads spec. The RPM of the spindle is based on the gear settings in the gearbox.
Thus for a particular thread type, the gear set is done than half out of the carriage is engaged with the lead screw, which enables the carriage to move /take power from the lead screw.
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