Scott S. Logan wrote:
Actually, it's 900 pounds of THRUST on the carriage.

900 lbs! So, if you rigged some pulleys, the lathe could lift itself
off the ground? That might be convenient for getting it onto skates for
moving BG

As far as lead screw torque: an 1/8" pitch, 3/4" diameter leadscrew has
a PI*3/4 / 1/8 mechanical advantage. About 19:1. So 900 lbs thrust
means 900/19 = 47 lbs tangentially on the screw. 47 * 3/8 (radius) = 17
in-lbs torque. I've ignored the friction between the leadscrew and its
half nut, as Mach. Handbook gives a value of .04 for worm gear at 250 fpm.

I don't know how big a "PL92" lathe is, but a clutch slip point of 17
in-lbs seems pretty low. The slip point is surely well above the normal
operating force. I measured 15 in-lbs on my leadscrew, but there is no
claim of precision or accuracy. Also, my assumption about the leadscrew
pitch could be wrong. The larger the pitch, the larger the torque for
the same thrust. (The assumption about the leadscrew diameter is
irrelevant - the diameter cancels out in the calculations.) If the
pitch were 1/4", the torque required to generate 900 lbs thrust would be
34 in-lbs. Or, my reasoning could be all wrong!


Bob