[Marwell]

Does anyone have a decent source for some 12mm prox switches. I need about 6 - 12mm NPN 4MM range 300m/a 6-36 volts..

Thanks,

Martyn.

[Mr.Chips]

This is a posting from Vince here on the Zone. I looks like a good idea.

Hall Effect Limit Switches
http://www.cnczone.com/forums/showth...t=31601&page=5

Z axis limit switches

My mill has been running great except for one thing. The Z axis limit switch trips at certain RPMs and cutter feed rate. It happens about once every 30 or 40 minutes of cutting. When the switch trips, Mach does and e-stop and I loose my X, Y and Z positions which then requires me to re-zero everything then do a “cycle start from here”, a pain in the butt. The limit switches are high end Omron (about $100 each). I tried varying the debounce interval, but it still did it when I passed 5,000 on the debounce.

Since completing the mill, I started on a Hardinge CHNC lathe. The Hardinge uses Hall effect switches for all limit switches. Once I saw how well the Hall switches worked, I figured they would great on the Z axis of the mill since they would be immune from vibration. I purchased several Hall switches DigiKey:
http://search.digikey.com/scripts/Dk...e=US5881LUA-ND
These switches are only $2.30 each. I made some switch mounts out of Delrin and epoxied the switches to the Delrin. Kirk had given me some 1/8” diameter magnets that are some special material and very strong. I epoxied one of these magnets to the Delrin piece mounted to the Z axis ball screw (see pictures).

The switches are three wires, 0V, +3.5 to 24V and output. I wired two switches in parallel (one for Z+ limit and one for Z- limit) to a CNC4PC C11G board with a 1K resistor across the +5V and pin 12 input. I then set up Mach for pin 12 active low. I lined up the switches so the magnet would pass about 1/8” away from the Hall switches. I ran the Z axis to both upper and lower limits and they worked perfectly!

After getting the switches adjusted I ran some test on the repeatability of the switches. I used a Mitutoyo digital dial indicator that reads to 0.00005” and is accurate to 0.0001”. I was amazed at the results. The Home Z axis repeatability was +- 0.00015”. No wonder Hardinge used this type of switch on their lathe. Just for the giggles I checked the back lash and found the Z axis to have 0.0004”. I kick myself for waiting so long to fix this problem. The total cost was less than $5 and some scrap Delrin, wire and a 1K resistor.

In the pictures of the switches, the white stuff over the wires is and epoxy putty to hold the wires in place.

Vince
Attached Thumbnails

[DareBee]

Are you anywhere near me?
I have MANY, MANY used ones and cables (cut you a cash deal).

Otherwise - I pay about 60 for Omron prox and maybe 25 for a cable.

[Marwell]

Darebee,
What I am looking for is some 12 mm proxes but I would like to change the ones on the machine I have. They are all sealed units with the 3 wire cable spliced into the main cable that goes back to the board. I have one switch busted right now but would like to change the cables as well, to a cable with an end that I can screw the new prox switches into. Much easier if I have to change a prox.

Send me an email [email protected] Maybe we can do a deal.

Martyn.