Leadscrew vs power feed shaft?

[Wheat.Millington]

What's the difference between the leadscrew and a power feed shaft, and when/why would you use each?

My little import lathe only has a leadscrew, no power feed shaft. So when I want to power feed I engage the half nuts on the leadscrew. It also has a separate crossfeed and powerfeed controls that engage a slot in the leadscrew - I don't understand why I would/wouldn't use this power feed versus the half nuts.

Because I've uinstalled an electronic leadscrew with its ratio based on the leadscrew pitch I don't use this power feed at all, however obviously I use this system for cross feed. Thanks.

 

[MrWhoopee]

The half-nuts are for threading. Cheap lathes use that for power feed, but that results in excessive wear on the half-nuts and leadscrew. Better lathes have a keyway in the leadscrew that drives a gear in the apron for power-feed. Even better lathes have a separate shaft parallel to the leadscrew which drives the power-feed.

 

[epanzella]

The power feed also has additional gear reduction in the apron which is too slow for threading. The half nuts grab the lead screw directly to bypass this stage of gear reduction so the carriage can move fast enough for threading.