Re: [CAD_CAM_EDM_DRO] Re: Servos', what type, what torque?

dpresto3@... wrote:

> My mill uses an R8 spindle taper. I will be using the machine for
> hobby work mainly, but I want to set it up so that the machine can do
> some fairly heavy work if required. The torques mentioned in the
> other posts in this thread, would they be peak torques? Would they be
> set up with a drive reduction of 2:1 or something similar?

Well, then, the 1000 Lb number sounds more appropriate. I've broken
3/8" end mills off in the collet wile carelessly jogging the table around,
so no more than 1000 Lbs is needed, I'm pretty sure.

Most of the ratings bandied about are continuous ratings. For steppers,
those are the max, too. Servos can generally produce peak torques of
about 4 - 5 times the continuous. I am using a 2.5 : 1 reduction on my system,
as that was what came in the axis drives I refitted.

You really need to work out the characteristics. It is not hard. A 2:1
belt reduction doubles torque, and halves speed. So, you should figure out
what speed and torque you require, and then work backwards through the
leadscrew and belts to the motor. The leadscrew throws most people.
Treat it as a drum with a string wrapped around it. For instance, a 5 TPI
screw can be treated as a drum with a .2" circumference, ie. a diameter of
.2" / Pi, or .06366". The radius is .0318". So, a full ratation advances the
table .2", and a torque of one in-Lb gives a linear force of 31.42 Lbs, if I
calculated that right. If the motor had a 2:1 belt reduction, then you'd get
62.84 Lbs linear force for each motor in-Lb of torque.

As for speed, 60 IPM equals 300 RPM for a 5 TPI screw, or 600 RPM for a
motor with a 2:1 belt reduction. IF you had a motor rated for 1000 RPM at
100 Volts, then it would need at least 60 Volts to make the 60 IPM speed.
Actually, it would need more, to overcome motor resistance.

Jon