Newbie- Limit switch Error

[friklin]

Hi there.

I just finished my first cnc mill. I run it an emc2 and ubuntu. The hardware is a 3axis set bought from Probotix. The problem I have is that I keep getting a limit switch error while running the cut. It seems to be random times and axis. I never come close to hitting any switches. Any ideas on what could be wrong.

[Gir]

There's either a lot of vibration causing chatter or a lot of noise in the line. Try using a shielded cable to run the limit switch.

[Richster]

Yes you either have a loose connection somewhere (assuming switch is normally closed) or you have noise in the system.

I had big problems with this. All my electrical lines are close together, so just activating the steppers was enough to trip the swithces, due to the electrical noise going into the parallel port. I know shielding can help in theory, but this didn't work for me.

I connected everything to the parallel port via opto-isolators in the end, which completely fixed the problem. There are probably other solutions too, but this one was relatively inexpensive and did the job for me.

Good luck - R

[Karl_T]

If you want top shelf, move up to Opto isolation. This would be easy with used parts off eBay. Get opto22 input modules that use 5V logic and a board to mount them. Hook your computer inputs to the computer side of this board. Use a higher voltage on the other side of the opto inputs. 24 Volt DC is most common.

Karl

[friklin]

Thanks I`ll try isolating the wiring first.

[blackbeard52]

Hook your computer inputs to the computer side of this board. Use a higher voltage on the other side of the opto inputs. 24 Volt DC is most common.

Karl
Take it a little easy on the newbies..... Could you give a diagram and maybe some part numbers for comparison as an example of your hookup. Most new machine builders dont know what a opto isolated anything is.

Bob

[mc-motorsports]

Wire your limit switches normally closed if you can, problem solved. Worked for me.

[Cartierusm]

Are you cutting wood or metal? I have some good cable but it's bunched together, but it's shielded. When I cut wood no problem, when I cut aluminum I have to turn the limits off because, I suspect, of noise.

[Gir]

Are you cutting wood or metal? I have some good cable but it's bunched together, but it's shielded. When I cut wood no problem, when I cut aluminum I have to turn the limits off because, I suspect, of noise.

Sounds more like a vibration issue. Wiring your switches normally open will fix chatter issues (unless you're getting some really bad vibes), and wiring your switches normally closed will help with noise issues (but might not completely fix them).