Re: ATM Mirror Grinding Machine

["Bill T." <twentiethwave@hotmail.com>]

mjc5 wrote:
> In my research on the drive systems for mirror grinders, I notice most
> are belt driven devices. I've seen some mention of DC motors, but not
> much detail beyond that. It seems that a slow DC motor (preferably 2 for
> directly driven use) would simplify construction a lot, and the variable
> speeds might be of utility during the grinding and polishing process.

Many DC servomotors can achieve full, smooth torque down to just a few rpm
and even less, when driven with an appropriate DC servo amplifier.  At the
big solar observatory here in New Mexico, many hundred tons of telescope are
rotated by a servomotor which doesn't even make one full rotation during the
course of day.  The motor system was costly, but elegantly simplified the
mechanics of the system.

When balancing the costs of building machines of many types, I have often
opted to reduce the amount of mechanical components (and the associated
machining) by using motors capable of high torque at low rpm.

Most servo amps can be wired so that a simple potentiometer can act as a
high precision speed control.

Surplus servomotors and amps are often available through surplus sources
such as http://www.servosystems.com.  Even from surplus this kind of stuff
is not truly cheap, so dust off your spreadsheet program.  As you add up
belts, pulleys, welding, pillow blocks, nuts, bolts, time etc. a low speed,
high torque motor can start to look pretty good.

Each person also needs to balance electronic vs. mechanical complexity in
proportion to his knowledge of both.

Bill T.