SFA

We've recently started using a CNC machine, and we've just been practicing edging and polishing straight edged slabs. Nothing fancy. Everything seems to go well with the first four bits. Our issue is with the last three polishing bits. We're noticing that a diameter difference of .01" will either mean the slab isn't being polished (no contact with the bit) or the bit is too close and becomes cracked. We've cracked two #5 polishing bits in the past 2 weeks.

Does anyone have any advice? Do I need to calibrate and reallign the polishing bits before running each template? Anyone else have similar issues with the polishing bits?

I hope I've been clear enough. This machine is new to us.

.01 is huge
try adjusting .oo1 or less
With polishing there should be very little amp draw

Also please go in to your profile and fill out you signature so we know who we are talking to.

It sounds like your polishers need to be reset up. As Chris said, adjust them in increments of 0.001". They need to be barely touching the stone. If you have any resistance when turning them by hand, it is too close. Patience is the name of the game when setting up polishers, which is not my best trait, but very important to not rush. Rushing is how you blow up polish wheels.

Thanks for your replies.

Follow up: What should the HP load be for the polishing bits? When the bits were alligned correctly, we were seeing .1 HP.

Randy
The horsepower will really depend on the style of polishers. With my polishers, running the correct RPM, they run at about .5 horse. Now this really depends on the torque curve of the spindle also, and I know the Park torque curve well. At 2600-2800 rpm thats where they should be. If you are running them at 4000 rpm(for example), the torque is going to be different and the horsepower needed will be much lower.
But from what you have said, I don't know if polisher setup is your only problem. You might be moving parts around with your metals and bringing your polishers into and "undefinable" tool path, and tearing to polishers up. There are a lot of variables that come into this.
I might be way off, but the fact that you are running with a .1 horsepower factor, and burning tools up, raises alot of red flags.

Feel free to call me if you want to talk about it.