Mill Spindle Feedback and Position Sensing

[macona]

I want to add spindle feedback and position to my vertical mill. I want to be able to home the position of the collet screw for operations like back facing or reverse counterboring a hole. Also having feedback would be nice for tapping. For velocity sensing I figure I could paint an encoder ring onto one of the pulleys. But this wont work for sensing the position of the spindle because the first time I put it in back gear the synchronization would be lost.

So heres what I am thinking. I have some Keyence FS-V1P fiber optic sensors with coaxial reflective leads with a little 3mm sensor head. They have a 250us response time. http://www.keyence.com/products/sens...ications_1.php

For the velocity feedback I could either read off the motor or spindle pulley. Its a varidrive setup so I would have to read off one of the fixed flanges of the pulleys. For the spindle I would pick off right at the nose. I figure I could could make a ring that attaches to the spindle cap that would hold the sensor head to the spindle. I could use some black lacquer or the like and make a mark in line with the collet screw. The ring would hold the sensor and protect the mark from swarf and coolant. I may have to make a seal or flange but the sensor should work even through oil from the spindle. With all of this it would still leave me with at least 3/4" of nose sticking out to hook my indicol.

I can mount the trancievers remotely and protect the fibers with some silicone fuel line or metal armor and some guides will keep them out of the way but still allow for quill travel. Its z axis is the knee so there is no quill travel during milling.

What do you guys think? Any better ideas?