[DennisCNC]

I am building a bridge saw to cut granite slabs and how would I estimate the horse power needed to move the gantry around? I will use 3 phase gear motors with VFD's and chain drive. The system will ride on very BIG THK rails. Weight of the bridge will be ~1,000 lbs, size 12 feet by 12 feet.

I went to a expo and they had a KOMO router there moving around at ~3,000IPM and I asked the guy what size servos they are using and he said they had 4KW on each side of the gantry.

I don't need it that fast.

This will be a manual machine for cutting straight lines with a diamond saw.

Any tips welcome!!

[Al_The_Man]

It all depends on how much gearing, how fast you want to go etc, for point-to-point positioning the constraints are not as high as for interpolated axis, also you will need to factor in the cutting forces, which if you have a present set up can be measured.
4kw is a liitle over 5hp.
I saw one gantry about this weight that ran on light railway rail and had a rack&pinion for drive. Remember that maximum torque usually occurs at acel and decel. Minimum generally occurs at rest and at-speed.
Al.l

[DennisCNC]

I will probably build the entire machine and then meassure approx. force needed to move it while cutting and not cutting and then find the motors. Not a engineering approach but will work for this time.

[jimbo]

Roton has a handy formulas

http://www.roton.com/web/application.6.jsp