Cutting grooves on a manual lathe often produces chatter that transfers into workpieces and causes poor surface finishes. And the larger the groove, the more chatter.
I initially tried adjusting speeds and feeds and the cutting tool's geometry to combat this problem. Now, I run the lathe in reverse and rotate the cutting tool 180 degrees — cutting on the upswing rather than down into the tool — to eliminate chatter.
I believe this method works because most, if not all, of the lathe's bearing wear is from cutting counter clockwise down to the tool as opposed to clockwise up into the tool. Since implementing this procedure, I have cut many grooves in a multitude of different shapes, materials and depths with no chatter.