Originally Posted by
adbuch
....1. It was pointed out to me by the local machine tool dealer that the lever type collet closer allows one to open the collet while the spindle is turning. Under what circumstances would the lathe operator want to do this?...
When you are parting off from bar stock and have a bar feeder sometimes it is much quicker to open the collet and let the bar advance against a live stop instead of stopping the spindle. Similarly if you are doing second operation work with a stop inside the collet sometimes it is quicker to load and unload with it spinning; so long as your parts don't have sharp edges.
Regarding quality you need to look at the way in which the lever actuation is transmitted to the rotating parts. Some closers just have cast iron sliders running un a groove; much like the selector forks on a gearbox. These can wear rapidly. Other types have a thrust bearing to take the rotating force.
An open mind is a virtue...so long as all the common sense has not leaked out.