Thinking about rebuilding my mill turn spindle soon to get more rpm out of it. Right now it's geared 1 to 1 with a 1.8kw dmm servo using a timing belt which gives me a bit under 3k rpm. I'd like to get closer to 4k. Since im geared 1 to 1 right now, I'm able to just use the z pulse from the servo drive for both homing and index pulse when turning. Once I gear it up 1 to 1.3 or so, z pulse will obviously no longer work for home when switching back and forth from turning and 4 axis indexing.

So what type of switch is gonna give me the best repeatability for homing? Mechanical switch is ruled out since it needs to turn continuously. I've heard optical switches are very accurate but not used often on cnc since a small chip can trigger it, but the belt and sprockets on my mill turn are completely enclosed so I don't think that will be an issue. Is an optical switch gonna be the most accurate choice? Any recommendations for a specific kind? This is run on mach3 and I will be writing a custom homing macro for best speed and accuracy for homing. 2 or 3 stage. First home at high speed, then back off and home again at very low speed, possibly again a third time at ultra low speed. Not sure how exactly these sensors work, but I'd like it to sense out on the edge of my disk brake which is 7 inch diameter. To get the accuracy I want, it needs to be able to repeat within less than a thou, preferably 5 tenths out at this diameter.

Also to make things more complicated, I might want to use these to improve accuracy on 90 degree indexing. Right now 90 degree indexing accuracy is only as good as about 0.1 degrees because of belt backlash, belt variance, and encoder error. So aside from home, I want it to reference a switch for each 90 degree index. I already edited my post processor to handle the disk brake automatically before and after each A axis move, so I should be able to implement something in the macro used to lock the brake after a move. Before locking, it can back up a couple degrees and index to the switch, then lock. This would require either multiple switches, or multiple pick ups. Either way, each point needs to be adjustable and it needs to know which is home. I'm thinking maybe 2 switches, one of them only sees one pick up for home, the other switch can be at a slightly different radius with 4 90 degree pick ups.

So really I'm just curious what would be the best choice of switch for this application, how to use it, and what kind of repeatability i can expect.