Proximity switches or limit switches

**chillybo** · 21-12-2019

Cropwell I've just been playing with the homing function and guess what? I did manage to run into the proximity switch. No damage though because I had my cursor on the reset button in Mach 3 and the switch mount wasn't fastened down. What I can't understand is why is the proximity switch detecting the gantry, stopping and backing off as it should but then moving forward crashing into the proximity switch. Could it be because I haven't set my steps per mm properly yet?

**pippin88** · 22-12-2019

Long time since I've used Mach 3, but likely you have the direction of the final homing move or the position of the switch (in software) set wrong.

Mach 3 thinks it needs to do a final move in that direction.

I could solve it if you were using LinuxCNC.

**cropwell** · 22-12-2019

Jogging seems to ignore home switches.

**Kitwn** · 22-12-2019

Originally Posted by cropwell

Jogging seems to ignore home switches.

Time to set up the soft limits before bolting that end-stop in place.

**chillybo** · 22-12-2019

Ive changed homing settings in Mach and it woks fine now. Other problem was the steppers were stalling but I've increased the current output on the drivers and its flying along now.
Just need to learn how to work out steps per mm with my 2005 ball screws and 26 teeth driver pulley to 22 teeth driven ratio.

**chillybo** · 22-12-2019

Motion
https://www.youtube.com/watch?v=1iJ4v9MIKRA

**JAZZCNC** · 22-12-2019

Originally Posted by chillybo

Ive changed homing settings in Mach and it woks fine now. Other problem was the steppers were stalling but I've increased the current output on the drivers and its flying along now.
Just need to learn how to work out steps per mm with my 2005 ball screws and 26 teeth driver pulley to 22 teeth driven ratio.

Don't fry your noodle trying to work it out just let mach3 do it.! . . Go to the Settings tab, just above Reset there's a button says "Set Steps per unit" this will work it out for you by moving a distance you tell it and by measuring the actual distance it moved it works out the Steps per required.

**chillybo** · 23-12-2019

Thanks for that information Jazz. My noodle is easily fried. I used a digital calliper and let the gantry push it up against a stop on the rail. Ive unwired it all now because my control enclosure was delivered today. Im going to use the proximity sensors for homing and mechanical switches for limits. I'l position the limit switch so the gantry just touches it without switching when its detected by the proximity sensor. That way if the gantry goes to close the sensor it'l trip the limit before it damages anything.

https://www.youtube.com/watch?v=HZF8jKtbkvo

**JAZZCNC** · 24-12-2019

Originally Posted by chillybo

Thanks for that information Jazz. My noodle is easily fried. I used a digital calliper and let the gantry push it up against a stop on the rail. Ive unwired it all now because my control enclosure was delivered today. Im going to use the proximity sensors for homing and mechanical switches for limits. I'l position the limit switch so the gantry just touches it without switching when its detected by the proximity sensor. That way if the gantry goes to close the sensor it'l trip the limit before it damages anything.

Your setup is not a good one.? Often when you crash into limits it's not slow like your doing in testing, it's usually at rapid feeds or higher cutting feeds when machine loses position
by missed steps due to things like Sticktion or binding, etc. In cases like these, the gantry doesn't stop instantly and you get over travel which will smash your setup to pieces.

You need to ride over switches, not into them.!

**chillybo** · 24-12-2019

Point taken I'l change it when I put it back together. If what you say is a possibility of happening then how do we guard against other things getting damaged like BK / BF bearing blocks? Is it therefore wise to leave a good margin of rail / ballscrew for stopping distance?