Of course you should have at least one limit switch per axis, unless you just set your X0,Y0 in the middle of your table, but then you'd really just not be getting the maximum out of your table, right? I've got two typical roller limit switches on the X- and Y-axis, and a tiny micro limit switch on the Z-axis. I set the limits on the X- and Y-axis to be both Minimum and Home, while the Z-axis is just Maximum. In EMC I can set the height of the Z-axis to wherever I want and then click the Z home button and it automatically sets it to zero.
Getting the limit switches mounted in the right place was a little tricky. I had to custom build the brackets and plates that would activate the rollers, but once they were set, they did fine. I also opted to put the X-axis limit actually on the gantry, that way all the limit cables come off the gantry in one bundle.
I found some really slick cable carriers online made by Nylatrac, but they are incredibly expensive and I was pushing the limits of my budget already. So after digging around a while online I found them on McMaster-Carr. Go figure. I bought two 3' lengths, with the Y-axis length being wider due to extra motor and limit cables. Nylatrac and the makers of my plasma torch cable (Thermadyne, incidentally, makes the torches for Miller machines) said the minimum bend radius was 8". Eight inches? I asked are you sure you don't mean diameter? Nope, radius. That meant my carrier would have to have a 16" diameter loop and that was way too big for anything I could have used. So after looking at pictures online of commercial rigs and many home-brew tables, I said to heck with it, I'll make it work, and ordered the biggest radius carrier I could get that would still fit on my table. And it ended up working perfectly.
The first picture is the X-axis limit switch. Note that bracket I had to weld in place to trip the roller.
The second picture is the Y-axis limit switch. Since that picture was taken I had to shift the Y-axis +2", so there is a little piece of steel to push it up.
The third picture shows an up close fo the Z-axis limit. I accidentally ran the sled up into it before I got it wired in and bent the little spring roller so I had to go back and rebend it and then watch more carefully to what I was doing. Live and learn.
The fourth picture is of the Y-axis cable carrier. It has two motor cables, three limit switch cables, and the plasma torch cable. I think they look pretty slick, and they certainly add to the "professional look" of the whole table.
The fifth picture is the X-axis cable carrier. I've seen a lot of people that get a cable carrier long enough to go all the way across the axis, but what for? If you can properly support the cable bundle while it heads for the other end, there's no need to spend the money for that length. So I didn't.
The sixth picture shows the completed Z-axis. I've got a removable plate that the torch clamp sits in (it's actually the clamp ring from the Miller circle and line cutting guide) and the whole thing can be unbolted and removed. If I wanted to make an adapter that held a Dremel or a wood router or even a pen, I could bolt it on right there. |