Turning off limit switches

[daniel]

Hey Guys, My limit switches keep coming on even thought there no where near the little metal piece that they normally activate at. Is there a way to shut them off? What would cause them to light up and stop at random?

[richards]

Daniel,
Welcome to the world of electrical noise. Don't worry, you're not the first one to experience it. There is no cure. Believe me. I just finished re-wiring my Alpha about an hour ago, using every proper wiring practice that I've picked up in twenty-five plus years of building process control computers, and I still had a couple of small jerks (the machine, not the people around here), when I ran the spoil-board flattening program.

What I have found to help is to run a THICK ground line to all axes. I drilled 1/4-inch holes in the rails on each axis and then used a 3/4-inch spade bit to remove the paint from around the hole. Next I used some 12-guage insulated speaker wire from the local Home Depot and crimped on lug terminals. Finally, using 1/4-inch bolts, washers, lock-washers and nuts, I securely fastened the ground wire to each axis, the control box, the computer's case, and the ground line to the power panel. There is no measurable resistance anywhere on any part of the steel table, the axes, the control panel or the computer case.

In the past, I replaced all of the Shopbot supplied switch wiring with shielded cable with the shield connected to the ground point listed above. Be sure that only one end of any wire is connected to ground so that you don't create a ground loop.

Most of the time everything works; however, there are some electrical gremlins that just refuse to die. The cold dry winter air doesn't help. Sometimes I can run for several days without any kind of hiccup. Other times I get a little random jerk. Most of the time that little random jerk doesn't do any damage to the piece being cut, but other times it leaves a little divot that either has to be sanded out or filled in with bondo.

Good luck.