Fixitt: Point taken with metal-on-metal wear

Irving: The problem is not so much whether the G540 can take the voltage as is there any benefit (the filter capacitors start getting pricy as the voltage increases)

CarbideBob: Thanks for the feedback & suggestions, I did some calculations and the bulk of the torque requirements appear to come from the leadscrew / motor rotational intertia.

Warning: Calculations follow...

Motor rotational intertia: 480 g.cm²
Leadscrew rotation interia: 687 g.cm² (includes coupler and handwheel)
Total rotational intertia: 1167 g.cm²

Screw ratio: 1 mm = 2 pi radians
Assuming an acceleration rate of 100 mm/sec² => 628.3 rad/sec²

Torque due to rotational intertia = Inertial x rotational acceleration
Torque = 1167x10^-7 kg.m² x 628.3 rad/sec² = 0.0733 N.m
[10^-7 is the conversion from g.cm² to kg.m²]

Force due to acceleration of load = Mass x acceleration
Force = 16.3 kg * 0.1 m/sec² = 1.63 N

Converting the leadscrew axial force back to a torque is complex, see http://www.engineersedge.com/gears/s...alculation.htm for details (includes friction losses).

For the Sherline leadscrew the relationship is approximately:
Torque (N.m) = Axial force (N) x 0.001
Torque = 0.00163 N.m

16.3 kgs is the weight of the entire mill, this is way larger than anything that I would intend to cut but I am using this to prove a point. Even for this "worst case" scenario, the rotational intertia is approx 45 times larger than the acceleration of the load.

Factoring in the load due to cutting (see original post) the total torque numbers are as follows for an acceleration rate of 100 mm/sec²

Cutting force: 0.090 N.m (12.8 oz-in)
Rotational intertia: 0.0733 N.m (10.4 oz-in)
Mass intertia: 0.0016 N.m (0.2 oz-in)

Total torque: 0.165 N.m (23.4 oz-in)

From various stepper motor charts, at about 4000 steps/sec you should only expect 15 to 20% of the holding torque (most of the curves were for a 24 volt system). In the above case the total torque is 8% of the holding torque so there is a nice safety margin but not hideously excessive.

That was quiet a bit of an eye opener that the rotational inertia is one of the largest torque contributors

David Campbell