[plasmaics]

Hey all . First I don't know too much about the tuning or servo motors.... I looking to change my 5x10 cnc Plasma table Y axis from crappy roller motion to Linear Rail ..I was hoping to also change the drive from
belt to Rack and pinion ..I wanted to know if I can run the servo motor with the gear on the rack without a gear reducer ..Can I tune the motor for that ratio?

Thanks
Bob

[alan_3301]

You could, but it would be horribly matched. Any decently sized rack you find will need a pinion around 1" pitch diameter.
That would give you 3.13159" per rev travel.
If you want to utilize all the power your servos have, they should be at max rpm, when the machine is moving at max velocity.
assuming 3000rpms.
With no gear reduction, that would give you max speed of 9300 inches per minute. No way you are going that fast. Your resolution is limited also.
If your machine will be going 500 ipm max speed you would want around 18:1 reduction.

You could get tiny rack with a smaller pinion, but the load capacity would be reduced.
You could get a gear reduction box, but they are very expensive if you expect low backlash.
You might get around 6:1 with single stage belt reduction, gt2 2m belt, 15tooth motor, 90t pinion. that is probably not a good idea though, the 15tooth pulley is 9mm OD
You should research belt reduction to see what is reasonable.

[ger21]

And actually, you'll get smoother and quieter motion with a larger pinion, which would require even more reduction. People only use 1" pinions because higher reduction gets expensive.

Ideally, you want to gear it so your maximum target speed is with the servo running at about 80% of it's rated speed.

[louieatienza]

I think that being this is a plasma table, and there are no "cutting forces" to speak of, you probably could get away with a 10:1 planetary gearhead. I don't even think resolution comes too much into play here really. Nor power - you just have to push each axis around with good speed and acceleration. You might be able to drive the pinion directly with a direct-drive servo, but they're expensive even used, and you'll need the matching drive.