[chris trublic]

anyone have any plans for wiring the complete system, i have two ways i can go either 38 v dc servo motors or i also have stepper motors, what would be the best way to go. also rack or screw what would be the best here, power supply what do i need.

[jcc3inc]

Sir,

I used to be in the business of making plasma cutting machines (C & G Systems). We used all dc servomotors with all rack and pinion drives. Some of the reason was "We have always done it this way" but all our competition did that too--! Anyway, the CNC package we used, Burny, had outputs for DC servos and provisions for encoder position feedback.

In the hobby range, I see no problem with using steppers. I have made a "test" machine (to try out my CNC software) where I use steppers. They run 250 IPM and can go 1000 IPM if needed. They are simple to implement and with 10x microstepping, they run smoothly.

As to drives, there are many scenarios suggested. Since my experience has been rack and pinion, that's what I used. The rack can be 24 dr, 20 degree pressure angle, 1/2 x 1/2 (unless you are making a small machine). The 20 degree pressure angle pinions should have more than 18 teeth to avoid undercutting. (14-1/2 degree need something like 32 teeth minimum!) You should spring load the drive pinion into the rack. The loading force can be found as F = (max driving force) x tan(20 degrees); for a 100# force, that turns out to be 100 x .364 or ~37#. When you locate the pivot for the motor/gearbox drive, be sure that the axis of the pivot passes thru the rack pitch line; this assures that the engaging force when driving one way will be the same as when driving the opposite direction.

If you want to email me, I'll send you pix of my test machine. Uou can get some ideas from those.

Regards,
Jack C. jccinc AT owc DOT net

[chris trublic]

i would like to see some of your drive to get an idea. please send to [email protected]

[Weldtutor]

Chris
Do a search here on CNC Zone for: free plasma table plans

These can be downloaded & printed.

A section on wiring is part of the plans, or soon to be added.