Hall Effect Limit Switches

I've been playing with PMDX-171s (www.pmdx.com) as limit/home switches, and spindle speed sensors. They work remarkably well - much better than I would have expected. Properly setup, they seem repeatable to within +/- 0.0002". Unlike optical switches, they are tiny (0.6" x 1.575" x ~0.3") there is almost no risk of contamination by swarf or coolant. I plan to mount mine totally enclosed within UHMW enclosures, removing the screw connector blocks for the cable to minimize the height, and provide rubber wipers to clean off any ferrous debris than might interfere with their operation. Seems a much nicer solution than optical to me.

Regards,
Ray L.

I have used the Honeywell ones in another application.
http://dkc3.digikey.com/PDF/C091/P2479.pdf
The only thing to watch is that this type need a permanent magnet to operate, which can collect metal dust.
As opposed to the type that will detect a ferrous metal flag.
Al.

Today I made 4 axes worth of enclosures for the PMDX Hall Efect switches, to become my home/limit switches. I elected to remove the screw-terminals, for making the wiring connections, from the PCBs, as that allowed me to make the housings considerably smaller. I'm also de-soldering the Hall sensors from the PCBs, and re-orienting them, so the PCBs can be aligned to the axis, making them long and skinny, with the long side parallel to the axis motion, and easier to mount in a tight place. As it is, they are 0.8" wide, 2.55" long, and 0.6" tall.

There's a two-piece UHMW housing, with a recess the PCB snaps into. The two pieces of the housing fit together snugly enough, they should be completely water-tight when installed. The cables will come out through the angled sides, and be sealed with adhesive. The two circlular dimples on the inside are for the LED on the PMDX board, which lights up when the Hall sensor triggers. The dimples are cut almost through, so the LED will show through the UHMW, and should be clearly visible from outside. The smaller piece holds the magnet, which is a 1/4" diameter cylinder, 0.130" tall. You can see a magnet slipped into one of them in the photos. Two of these magnet brackets will be mounted on each axis one near each end, with a single Hall switch mounted near the middle of the axis. The magnet just needs to pass within about 1/4" of the Hall switch. A wiper will be provided to wipe off any ferrous debris that might be attracted to the magnet. With the UHMW housings, any debris wipes off VERY easily and cleanly.

The X axis switch will be mounted to the middle front of the saddle, just below the way, with the magnets mounted to the underside of the front tray of my table enclosure. The Y axis switch will be mounted under the side of the saddle, with the magnets mounted on the knee. The knee switch will be mounted on the side of the base, with the magnets near the opt and bottom of the knee. The quill switch will be mounted on the ballnut carrier, with the magnets fastened to the ballscrew housing.

These are VERY cool little devices, and remarkably accurate. In testing their accuracy and repeatability, they seem pretty consistently good for +/- just a few tenths. That probably increases if you test over temperature, but I'm not too concerned about that.

Regards,
Ray L.