Limit and Home Switch Choice

[Wobblycogs]

As always Dean a couple of very good points. I knew as soon as I said I was happy with the e-stop circuit that there would be something wrong with it , it's my super power.

As you suggested I've put in a relay and run 24V through the switches. Can I just check that my understanding of how this works is correct. I think this is a suitable relay. Since the voltage is 24V and the coil resistance is 2.8k will this portion of the circuit draw 23/2800 = 8.6mA? It can handle 2A across the contacts which must be about 500* what the PMDX will put through it.

I was using PNP sensors because I had a 24V supply already in the system. That's a really stupid reason to make life difficult for myself though so I've switched them over to using NPN. I assume 12V is sufficiently noise immune for this to not be a problem?

Is the two e-stop button arrangement a good / bad idea? The one at the top left will completely kill everything by removing power. I only envisage using that in "hand-being-eaten-by-the-machine" emergency and it will be on the control box (probably). The e-stop button connected to the PMDX is for "uh-oh-that's-not-good" type emergencies and will be mounted on the machine.

[JAZZCNC]

Okuma Howa Mill AC2 Okuma 5 Pin Limit Multiple Switch 5 Pin Limit Okuma | eBay
Recommend this style of switch as they work almost as a scraper of the Dog as it travels over and very high position accuracy

Ah ah this is DIY CNC.!!. . . I can buy all the ballscrews for a Small machine for less than that.!! . . . . . . Completely OTT in this case.

E-Stop are EMERGENCY stops, so should be wired for YOUR protection. When you've got your hand wrapped around a cutter, you won't have time to ponder on which E-Stop to press...

Very very true I ounce got my T-shirt caught in the Long timing belt that runs across back of my machine and I can tell you I shit myself.!! . . In the Split seconds it happened It Didn't even enter my head to hit the E-stop.!! . . Looking back it was very Funny.!! . . Belt grabbed it and started pulling me into the pulleys I fought back pulling away and we wrestled until it had half peeled the tea shirt off my back before the material thru the belt off the Pulley. . . Looked like something from a Cartoon. . .Lol (didn't learn from it either has there's still no covers on belts. . Lol)

I've put my axis limits in series with the E-Stops because a near-crash IS an emergency. As for your feedback, you simply use another spare aux contact on the relay to make or break the BOB com/5v link.

Don't Agree but Know what your saying. Hitting the limits isn't really an emergency it's a machine positional error and no different from missed steps which you wouldn't hit the E-stop for, or should say want to Kill power for.
Really it comes down to how you want to stop the machine if some thing goes wrong, that could be a serious situation or just because you see something like it's going to hit a clamp etc.? There's several ways to look at it.!

When it's Minor then you just want to Halt the machine movement so Feed hold is best, you don't always want the Spindle or Coolant, Vacuum etc to go Off. This could be the case with the Limits has it's only lost position why would you want the spindle off or Vacuum.? Turning the spindle off could damage the tool if it's still in the material, same goes for vacuum no need for it off.

When it's serious has in E-stop you want every thing OFF all power Killed.!

Is the two e-stop button arrangement a good / bad idea?

Yep I would drop the E-stop in the limits circuit and just have E-stop Kill power. The PMDX has feature to MACHINE HOLD just wire this in with the limits relay and let it do the work.

[birchy]

Don't Agree but Know what your saying. Hitting the limits isn't really an emergency it's a machine positional error and no different from missed steps which you wouldn't hit the E-stop for, or should say want to Kill power for.
Really it comes down to how you want to stop the machine if some thing goes wrong, that could be a serious situation or just because you see something like it's going to hit a clamp etc.? There's several ways to look at it.!

When it's Minor then you just want to Halt the machine movement so Feed hold is best, you don't always want the Spindle or Coolant, Vacuum etc to go Off. This could be the case with the Limits has it's only lost position why would you want the spindle off or Vacuum.? Turning the spindle off could damage the tool if it's still in the material, same goes for vacuum no need for it off.

Soooo, should the limit switches be in series with the E-Stops or not? I've essentially got 2 mains supplies - one direct to the PC, Monitor, 24V PSU, etc and one switched through the safety contactor. When a safety switch is activated, it kills the power to the 42V steppers PSU. I haven't fitted the spindle VFD yet, but it will use the "safe" supply as I'll want the spindle to stop when I hit an E-Stop. But with the limits in series, an overshoot will also cause an emergency stop. Is there a better way of doing this? I don't want to rely on software to handle E-Stops.