Re: ATM hydraulic grinding machine

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

>Nice idea, but the hp required to drive a power steering pump is a lot
>higher than what you would need with straight electric drive. Why not
>shop around for some linear actuators. Or build them yourself? Chicago
>Gear has a wonderful collection of bits for building up stuff like this.

Linear actuators tough enough to take the extended duty cycles of polishing 
are pretty hard to find surplus, and very expensive new.  The most common 
satellite-dish-aiming actuators aren't rugged enough, and the gear ratio is 
way too fine.

The required reciprocating motion could also be obtained from a puck moved 
back and forth captured in something like a "U" channel, driven by a chain 
loop.  My next Gort machine will capture the arms on "Dual V" bearings and 
loop driven shuttles obtained from Bishop Wisecarver.  In fact, it is 
probably possible to build an adequate reciprocating arm carrier with with 
sliding door components obtained at -- you guessed it -- Home Depot!  Not 
the household stuff, but the heavy duty barn door stuff.

One disadvantage of the enclosed ball-screw cylinders I use now is that it 
is time consuming to disassemble them for lube and maintenance -- an exposed 
dolly-type mechanism would be much easier to maintain (and more dangerous!).

Gort experience suggests that for a 30" machine using polishing laps up to 
20", about 1/4 hp. per arm actuator would be adequate, or about 1/2 hp. per 
arm actuator for full sized laps.  This assumes a transmission that lets the 
motor run comfortably within it's optimum performance envelope.

While CNC is nice to have, it is also possible to rig up "dumb" 
reciprocating devices with relays and impact switches at each end of travel, 
that cause the motor to change direction each time a switch is encountered.  
Of course, the same could be obtained by a standard circular-reciprocating 
system as on most Zeiss, Draper, and similar polishing machines.  But I have 
found that "linear velocity profile" polishes is faster than the "sinusoidal 
velocity profile" of traditional machines -- the motor speed stays high for 
a larger percentage of the total stroke, and the effect carries out to the 
edge faster.

Bill T.

relatively cheap reciprocating motion stuff:
http://www.bwc.com



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