[fatoldman7]

I work in a research lab, and we have been milling tissue samples imbedded in plastic. We have been using a Taig CNC mill as a proof of concept device, but we would like to build our own machine. The process goes like this: Place sample in vise, take a .0003 cut across sample with a 1.500 shell mill, stop spindle to lessen vibration, move over to microscope to image, turn on spindle, and repeat. This can take over 24 hours, depending on sample size. In the end, the images are stitched together to create a 3D image of the sample
What I need help with is what type of bearings to use for our spindle? We would like to run the spindle at least 10,000 rpm, and for long periods of time. There are no real cutting forces, and the greatest load I can see the spindle taking, is the torque it would see getting it up to speed.
Any help pointing me to the right type of bearing to use would be appreciated. I've tried talking to a few custom spindle manufacturers, but they seem to want me to supply the designs, not them. I tried looking at the various bearing manufacture's web sites, but I can't seem to find the information I'm looking for and get bogged down, start feeling dumb, and get the urge to nap.
The other issue is how to drive the spindle. We have been thinking that a belt drive would be best to lessen vibrations from the motor being transferred to the spindle, is this sound thinking? Also, what is the maximum speed a small belt drive can run at? Or should we be using a direct drive motor?
In the end, I was hoping that a simple aluminum block, with two of the right size/spec'd ball bearings, running by belt to a motor, would be good enough to get the job done.
Thanks for your help!

[awerby]

The bearings in your Taig spindle can run at 10,000 RPM all day long if they were properly run in to start with. It is already belt-driven and mounted on an aluminum block. That large a shell mill is not what I'd usually recommend for this machine, but given the very small depth of cut, it's probably not an issue. Getting a repeatable .0003" cut, though, might be asking a bit more than the stock Taig configuration can deliver. If it were my project, I'd leave the spindle alone and mount a precision actuator platform to the mill bed to do those tiny vertical moves. If the spindle motor is vibrating the mill bed too much, you might think about separating the column from the mill and mounting it independently, on something isolated from the rest of the assembly. Then you wouldn't need to stop the spindle and wait between each cycle, and things would go a lot faster.

Andrew Werby
www.computersculpture.com

[fatoldman7]

Thanks Andrew for your reply, we are building an all new machine, and plan on isolating the spindle, motor, and microscope from each other. The Tiag spindle has run for several days at close to 10,000RPM with no problems, other than getting a bit hot. The finish could be a bit better, whether this is a problem with the spindle, or the machine structure, or both, we are not sure. We are hoping that a larger spindle will give us a better finish, allow us to experiment with higher speeds, and control any heat issues. Another idea we have been discussing, is to use a electric motor from an large scale RC car to turn the spindle. Anyone have thoughts on that idea?

[mactec54]

fatoldman7

Will you always be using the same cutter 1.5" This is a big cutter for something like a Tiag, there spindle is not suitable for that size cutter, For motor some are using the RC motors, these motors don't like what you want to do though, they like to run at near there max RPM

Have you looked at the shear Hog cutters, they will do a better job than the shell mill, & need less power to drive It

http://abtoolsinc.com/prod/shear-hogs-shank/