help with servo motors Please.

[JAZZCNC]

What I did was work out the HP/Watts I needed then added some extra to cover any eventual loss.
I thought to drive a Cutting head through the stone Extra Torque is needed. and so higher Watt which also means Faster machine,
Profi stone machines cut 300mm per minute cutting granite shapes and cutting straight lines with High head 6 metres per minute.
im looking for comparable speeds to use the machine in a working environment cutting limestone which is about 2/3s the force needed

I'm not into cutting stone so don't know the speeds and feeds but what I can tell you is you'll need one hell of powerful spindle to cut Stone at 6mtr/min.!!

There's a huge differance between 300mm/min and 6000mm/min and I don't know of any cutting situation or material where you'd go so Much faster for straight cuts than you do for curved cuts other than slowing down for corners.!. . . . Are you sure they cut at these feed rates.?

Also if you running R&P I doubt you'll want to run it direct drive because the pitch will be high and resolution lower.? Chances are the Servo or larger stepper will have shaft size around 16-19mm so looking at my Ondrives catalogue this will mean Pinion size around 29T Minimum.
This will give Diameter of 43.5mm x 3.141=136mm. This will be the pitch so with 3000Rpm servo direct drive you'll have rapid speeds around 408mtr/min.!!!! . . . . . With a 2500PPR Encoder the resolution will be 136mm/2500=0.05mm
Even with Steppers you'll be at 136mtr/min (1000rpm x 136mm=136) and with 2000micro steps resolution will be 0.07mm.

To be honest I'm not sure 400W servos with heavy gantry with direct drive will be enough anyway so you'll want some ratio to increase torque.
Another thing you should be aware of with steppers is that higher Power(watts) motors doesn't always mean higher speeds, often larger motors spin slower than smaller motors. They will carry the torque higher up the rpm curve before stalling but will spin slower.

Now the other problem with servo's comes from the Pulse rate needed to get full speed is far higher than the parallel port can handle. So then your into expensive Motion control boards and Breakout boards that can handle the high pulse rates needed.
It's for this reason I feel steppers are better because the Cost doesn't just stop at buying the servos/drives. Then you have all the extra tuning setup etc that goes with them, where steppers are pretty much Fit with quick setup and forget.

For simplicity and reliabilty I'd go with Steppers and High Voltage drives with a 2 or 3:1 ratio using R&P. This setup will still give high rapid speeds and good resolution with good torque where it matters which is when cutting.