Proximity switches or limit switches

[JAZZCNC]

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]

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?

[JAZZCNC]

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?

Well BK/BF blocks are not easily damaged so wouldn't be too worried about them, stepper motors will stall before doing any damage. However, if you have anything that can be damaged then it's best to fit Sturdy bump stops after the limits. Skateboard wheels work well.!

[chillybo]

The plastic mounts for the limit switches I printed will actually slide down the rails and the extrusion if the gantry goes up against them (provided i use plastic slot nuts that I've designed and printed that will secure the mounts in place up until a certain amount of force). I could modify the print so that the rail carriages come into contact with the mounts after the limit switch is activated so it would slide the mounts and activated limit switch out of the way without damaging them. Behind this I could put a buffer as you suggested. I think this would work and if things did go tits up I'd notice it happening if I was looking. The mounts are cheap to reprint if they do get damaged. Next question is... is it worth using one off those PILZ relays to cut PSU/mains voltage off and does this stop movement quicker?
Thanks for all the advice.

[JAZZCNC]

The plastic mounts for the limit switches I printed will actually slide down the rails and the extrusion if the gantry goes up against them (provided i use plastic slot nuts that I've designed and printed that will secure the mounts in place up until a certain amount of force). I could modify the print so that the rail carriages come into contact with the mounts after the limit switch is activated so it would slide the mounts and activated limit switch out of the way without damaging them. Behind this I could put a buffer as you suggested. I think this would work and if things did go tits up I'd notice it happening if I was looking. The mounts are cheap to reprint if they do get damaged. Next question is... is it worth using one off those PILZ relays to cut PSU/mains voltage off and does this stop movement quicker?
Thanks for all the advice.

Then you have all the hassle of setting back up again and I don't think you realize just how many times or how easy it is to smack a limit when new to CNC and setting a machine up for the first time. To be honest I don't see the problem with making them slide past and do away with the hassle.? They also work better IMO but that's open to debate which I'm not getting into.

Regards the Pilz then you don't need it at a hobby level and while it might detect a mili sec or two quicker that won't change anything because it's inertia you are dealing with and couple of mili secs of movement is nothing.

[chillybo]

Probably won't bother with a Pilz then at least for now. I could make it so the limits / home are sideways on. I'm still a fair way off sussing out how to position the other axis switches but i do have options. I'm new to this lark and my preconceptions and concerns about damage have been more focused on the machine frame / bearings and ball screws etc as this would be more catastrophic and expensive. I really appreciate advice based on actual experience and I'm in no doubt that i haven't done enough research to get things right first time. Which ever way my machine turns out i'l certainly be keeping an eye on it especially when I'm cutting stuff that goes near the edges of the bed.

[Kitwn]

One of the main dilemmas with any DIY project is working out where best to direct the inevitably limited funds. Having never heard of a PILZ relay before I did a quick search and seeing what you have to pay for one, I agree with Jaz. You don't need one!

[chillybo]

OK guys so the plan now is to go with 3 proximity switches mounted sideways and now underneath the table one for homing two as limits. This looks like suitable place to put them.

[chillybo]

WiringDia_compressed.pdf

So this wiring diagram is how the home switch works. Next question is how do I wire two of the same NPN NC switches in series to act a limit switches.
Regards Chris

[JAZZCNC]

WiringDia_compressed.pdf

So this wiring diagram is how the home switch works. Next question is how do I wire two of the same NPN NC switches in series to act a limit switches.
Regards Chris

You are using an IP-M why would you wire them in series you're not short of inputs surely.? Wiring prox switches in series slows there reaction time so it, if not needed, wouldn't do it.

However, if you must do it then simply take the Signal wire (black) from first switch to the (0V) on the second and repeat for any further switches in wired series. On the last switch take the Signal to the IP-M (-)input.