[Daedalus308]

Hi Everyone, I'm with a student group and we are building our own cnc milling machine to gain experience in engineering and we are having some troubles converting our spindle. We have received a 15k rpm 40 taper belt driven spindle that we believe to be out of a haas mini mill and we are trying to convert it to direct drive so we can use our machine for rigid tapping. The tricky bit is that since the drawbar is in the center (shown in first pic), and the drive is on the outside of that, that means that we have to have some interesting intermediary system between the motor (intended to be a high speed servo) and the spindle to allow for automatic tool changes and minimal backlash to allow for rigid tapping. My question is, does anyone know how industry direct drive spindles in machines capable of rigid tapping accomplish this? In a different haas machine I see a pin and slot method (shown in pictures) that would work but I am worried about the clearance between the pin and slot being too large too accommodate rigid tapping. I have thought of using a tapered slot and a trapezoidal cross section to reduce backlash, but that's fully custom and hard to manufacture. Do y'all have any suggestions or industry knowledge that might help?

[mactec54]

Hi Everyone, I'm with a student group and we are building our own cnc milling machine to gain experience in engineering and we are having some troubles converting our spindle. We have received a 15k rpm 40 taper belt driven spindle that we believe to be out of a haas mini mill and we are trying to convert it to direct drive so we can use our machine for rigid tapping. The tricky bit is that since the drawbar is in the center (shown in first pic), and the drive is on the outside of that, that means that we have to have some interesting intermediary system between the motor (intended to be a high speed servo) and the spindle to allow for automatic tool changes and minimal backlash to allow for rigid tapping. My question is, does anyone know how industry direct drive spindles in machines capable of rigid tapping accomplish this? In a different haas machine I see a pin and slot method (shown in pictures) that would work but I am worried about the clearance between the pin and slot being too large too accommodate rigid tapping. I have thought of using a tapered slot and a trapezoidal cross section to reduce backlash, but that's fully custom and hard to manufacture. Do y'all have any suggestions or industry knowledge that might help?

You would use the belt drive and an encoder on the spindle for rigid tapping there is not much to it

[Daedalus308]

You would use the belt drive and an encoder on the spindle for rigid tapping there is not much to it

somehow that was actually something that we hadn't considered and i feel dumb for that. although we also want to do direct drive for a few other reasons (we will have a funky machine layout) so I think we'll stick with it

[maxspongebob]

A timing belt with 1:1 ratio is basically direct drive.
The benefit is a lot less complexity.

[spumco]

Direct drive spindles that I've seen - and there may be other layouts - are either:

1. Integrated spindle motors, or
2. Hollow-shaft motors.

Integrated means the machine builder buys a rotor & stator set from a motor mfgr with a specified bore & mounting arrangement. The rotor is slid over the spindle OD and fixed in place with the spindle bearings mounted outboard of the rotor. The spindle becomes the motor 'shaft' if you will, and any through-spindle features (drawbar, coolant/air/bearing lube/etc.) is passed though the spindle as usual.

The SKF Bearings web site has some excellent spindle arrangements - demonstrating their bearings, of course - but they show diagrams of integrated motor spindles as well.