I currently have roller micro-switches for home/limits on my knee mill, and they work OK. Repeatability seems to be at least 0.001". However, the little roller arms are delicate, and easily damaged, and, of course, they are not coolant/oil/chip friendly. I am switching to fully enclosed optical limits, which I expect to give much greater accuracy, and, being completely sealed, will be oblivious to all the nasty stuff flying around a mill. This also allows me to have separate home and limit switches in a small space, by putting two optos next to each other, both operated by the same flag.
You normally want to connect home switches as normally closed, and simply connect them all in series. There's no advantage whatsoever to having separately wired switches. Also, using normally closed, you'll know immediately if one fails. If wired normally open, you won't know if one has failed until you try to home, and the axis sails right past the switch and hits the hard stop. Similarly, all my optical switches are normally conducting, and turn off only when the home/limit is hit.
Regards,
Ray L.  |