I think Harry is right about the torque labeling. It is holding torque rather than driving torque. As a fer instance on my mill, I initially used 270 0z motors with a Xylotex driver. They did drive the axes well. I was using linear bearings and ground ball screws. They really lacked speed and holding torque though. Especially in the Z axis.
Ultimately I have went with 495 oz motors with Gecko 203V's. Now I have plenty of speed and holding torque, but I find I need a little more on the Z to be able to peck drill faster. I have a belt system that I am going to install on it. The screws I am using have a high helix too, so these motors would work better with a lower pitch. The pitch on these is 10 mm. Makes for a pretty fast and accurate machine, but could be even better with either larger motors or a belt drive on all three axes. I am satisfied with the other two though. It can rapid @ 300 IPM but that is crazy fast for a mill this small. I rapid @ 200 IPM on X and Y and 125 on Z.
Back driving is what its called I think when the motors don't have enough holding torque to keep the still axis from moving away from the cut. Bigger motors or gearing are the fix. Drivers have a lot to do with getting the most out of the motors too. Gecko's out preform Xylotex simply by supplying more amps and voltage to the motor. Other reasons too, but you pay for that output. Very well worth it though.
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Lee |