cnc for marble

[JAZZCNC]

Don't get me wrong rack and pinon is great for soft material routers that need high speeds but I don't think it's correct for your application. Of course you could probably make it work but it wouldn't be the ideal solution.

Sorry but your wrong R&P is the perfect choice in this application. Just about every industrial Stone cutting machine uses Helical R&P.
Your also Wrong about the Resolution and Micro steps because no one who runs steppers would run at FULL step 200ppr. WHY.? . . . Because Resonance and the affects it has on the motors is crippling to motor performance when full stepping. Infact you'll be hard pressed to find decent quality drives that provide Full step mode. Half Step(400ppr) is usually minimum. In real world use then between 800 and 2000ppr are used to give best balance of performance/smoothness.

In this application cutting hard material and Steel framed machine the resonance will be high so using higher micro steppping would be used to help smooth motor performance. Micro stepping however shouldn't be thought of as way increasing resolution, though it does to some degree dependant on motor quality.

Resolution should be calcualted based on pitch. R&P will minimim ratio of 3:1 (typical 5:1) dependant on several factors like Pinion size, motor Rpm, desired Rapid speeds etc.

Lets look at it again with realistic figures using same pinion size. Lets start by applying a minimum Ratio 3:1 with minimal 400ms setting and seeing the speeds, resolution this would give.?
With an affective pitch of 79.833 / 3=26.611mm pitch which based on usable RPM of typical motor used being 700rpm this would give 18627mm/min or 18.6Mtr/min which is ridiculous speed for cutting stone that would never be used.
The resolution would be 26.611 / 800=0.066 which is still more than enough resolution.

Now lets go to more likely setup that would be used. 5:1 ratio still giving a speedy 15.966 Pitch and using 1600Ms which is often optimal for motor smoothing.

Rapid speed: 15.966 * 700= 11,176mm/min or 11.1Mtr/min still a nice healthy speed which you'll never use cutting stone other than for positional rapid moves.
Resolution: 15.966 / 1600= 0.009 far more than needed.
Now the Resoultion figure isn't exactly true figure but rather theoretical figure and in reality there will be some mechainical loses but the higher it is to start with the higher it will balance out to in the real world.

Also the higher ratios have increased torque which will be needed with R&P because it's quite inefficient compared to ballscrews so will need more power.

Helical R&P it's better than straight cut and provided you protect it from debris and keep pinion tensioned into rack properly then it's the perfect solution for long machine like this.