Mach3 user - how do home switches work?

Yeah. Limit switches should cut the electrical power to the motors by means of relays, not computers, precisely so confused CNC cannot break the machine.

Joe Gwinn

There are two reasons to put switches at known locations in the travel of an axis:

If your software is really using the switch as a _home_ switch and not a _limit_ switch, then it will only pay attention to the switch when it is homing -- and the homing algorithm will be something like "move the axis toward the home switch at a known safe speed until the switch opens, reverse direction and move _really slowly_ until the switch closes, then call that spot 'zero'".

And, if your software is really _just_ using the switch as a home switch, then it'll happily go "past zero" in normal operation.

Trying to implement a "don't crash" limit switch when you've got a motor that takes a while to stop even at maximum opposite current is a pain in the behind, because the mechanism _will_ keep moving for a while after you slam on the brakes when its going fast, but if you approach the switch slowly you'll need to power it in the desired direction to get it to finish up. About the only way out of that quandary is to have a normally-unused "shut-down lane" -- and who wants to pay for unused travel in their machine?

IIRC you also have to enable the home switches in the axis or motor setup dialogue.

MikeB

I'm not much help at all really but, I just finished setting up limit for z and homes for x, y and z, I went around a couple times in circles, I ended up not having the correct number in the port settings, so "I'm not sure if that helps you or not, I had to go to the manufacture for help, which they were a great help and I can only hope I remember everything they did in the future

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I don't know Mach3, and it is probably a configuration in there somewhere. Something along the lines of "When you sense this -- STOP!", instead of "When you sense this, make a note in a logfile or on the screen and keep on truckin'. :-)

Or is there a "E-stop override" in Mach3 somewhere? Could this be engaged?

But first -- are you using steppers or servos? Steppers stop as soon as the computer stops talking to them. Servos keep moving at the last commanded speed until the computer says to change to zero inches per second (0 V command input to the servo amp).

And in either case, the stepper driver or the servo amp should have a separate input to inhibit motion. This really should be connected. (Some servo amps have separate inputs to inhibit motion in the two directions, so you can have two limit switches, and still be able to feed it commands to back it off the limit switch. It would proably be easy enough to add those to stepper drivers too, if they don't already exist.) The "stop in any direction" input connects to the E-stop red mushroom button.

Good Luck, DoN.

Did you start here?

There is a difference between home switches (used for homing, which means precisely determining the coordinate system), and limit switches, which are used to activate the E-stop relay. The best practice is not to combine these functionalities in one.

Many thanks for all the suggestions guys - for now I've given up!

The switches work and the software senses them in diagnostics mode but I cannot get them to work as limit / end of travel switches.

My machine is generally working & other issues like getting a better spindle than the existing Dremel are higher priority at the moment.

Cheers

When you ask something again, I'd consider a forum with a large Mach3 user base. CNCzone.com is one example.

Karl

Thanks Karl, I will.

or the machsupport group

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Thanks