home, limit, e-stop

[drafterman]

I am very new to the whole scene, but during my reading I see very little discussion about home/limit switches or e-stop buttons. Does not everyone use these? I also have read that the interface wiring of limit switches to motor driver boards can be tricky so as not to damage the drivers. Any schematics or advise would be appreciated. I am going to use xylotex boards with my stepper motors.

Also, on the z-axis for plasma torch height (non digital controlled)...how do you set your zero height? Do you just design in enough over travel in the axis that the transfer balls allow for this?

[Weldtutor]

Originally Posted by drafterman I am very new to the whole scene, Also, on the z-axis for plasma torch height (non digital controlled)...how do you set your zero height? Do you just design in enough over travel in the axis that the transfer balls allow for this?

Hi & welcome to CNCzone

To zero your plasma torch Z axis, jog the transfer balls down to lightly contact the work surface, then "zero" your z axis in the control software (Mach or other.)

Your g-code will then use this zero to offset for pierce & cut heights.

You might get more response to questions in the plasma "discussion" area rather than the project build log.

[GaryCorlew]

Here you go: http://www.solsylva.com/cnc/xylotexdrive.html

[drafterman]

Thanks for this. I notice from the Xylotex website that the ports are not isolated on their board. This is why I wonder if a breakout board is recommended? Also, I know you can wire an e-stop in the same method, but shouldn't the e-stop also shut down AC power in addition to signaling the software to stop movement?

[jon..duke]

An inexpensive E-stop button can be made using the headlight switch from any of the autoparts stores. The AC power to outputs controlled by the computer e.g. relays controlling router motor, blower, coolant etc is killed with an estop.

[massajamesb]

I have a breakout board that has all the inputs for limit, home, and Estop switches. A trip of the Estop tells the software to stop, puts an electronic brake on the motors, and turns my plasma off, all immediately. It is instantaneous, really.

All of these inputs are isolated through the breakout board.

[Pete Stenabaugh]

Originally Posted by drafterman I am very new to the whole scene, but during my reading I see very little discussion about home/limit switches or e-stop buttons. Does not everyone use these? I also have read that the interface wiring of limit switches to motor driver boards can be tricky so as not to damage the drivers. Any schematics or advise would be appreciated. I am going to use xylotex boards with my stepper motors. Also, on the z-axis for plasma torch height (non digital controlled)...how do you set your zero height? Do you just design in enough over travel in the axis that the transfer balls allow for this?

The interface for limit switches and e-stops is easy. To hook up home switches is also not bad, but it depends upon how accurate you need the home switches to be.

I would suggest that you check out www.cnc4pc.com, and check out their break out boards. I have recently installed the C-11 board, for use with Mach 3 and gecko drivers. It supports all of these features and the hook up is pretty straight forward. The designer Arturo Duncan is also very willing to help you out with information. Check him out and/or send him an email. He is located in Florida.

Pete

[davidmb]

just be careful what you turn off with an estop, just killing the ac power maybe ok but if you use vacuum or hydraulic clamping you dont want the workpiece loose, some spindles take time to stop.

[Pete Stenabaugh]

David you are quite correct. With the C11 board, the way it is wired up the incoming +5vdc goes directly to the board. There is a splice on this line that also goes through the limit switch first, then after the limit switch the +5 goes to the board and thru the limit switches (nc contacts wired in series). It all works very well. I forget the actual schematic but it is available from cnc4pc for the asking. Hitting the E-stop will not cause the power locks to disengage. The C-11 board has also got a safety charge pump for this purpose if you need it.

Wired this way, in Mach 3 you initialize the auto limit override in the settings screen, so that when you hit a limit switch, the machine will stop, the 'reset' button in Mach will flash. You then reset the button in Mach and you are then able to jog your machine off the limit switch, then hit the reset button again, and away you do. You may or may not need to reset the machine location when doing this. I have my digital readout running at the same time, so it gives me an easy way to reset the location if needed.

Pete.

[Torchhead]

The Mini-IO Breakout card has a direct connect ribbon cable for the Xylotex 3 or 4 axis drives buffered step & Dir for 4 axis, 2 high current relay drivers and opto isolated inputs. The basic unit will provide for all of the inputs and outputs for a single parallel port and it's self powered. Other options canbe added with the unit or at a later date.

The manual for the MINI-IO and expansion products is at:
http://www.CandCNC.com/Mini-IO-2-Manual-REV2.pdf and has information about hooking up limits and homes.

Tom Caudle
www.Candcnc.com/Mini-IOProductsChart.htm

[scheek]

I have a free "How I build my own CNC" somewhere on this site. (scheek). It may help. You can see the limit switches I used. Yes, you must have them. I've used mine and estop numerous times. I hooked all my limits switches in series and wired them to (I think the Y limit on the breakout board. It doesn't matter which one...just pick one). Mainly because it's obvious to you as to which one is hit during operations. I'm trying to remember, but I think I removed the installed estop jumper (which bypasses all limits switches) on the breakout board and then just hooked the the new limit switch wires to the one of the XYZ limit switch connectors. This replaces the Estop jumper (to me this should have been called the limit stop jumper). When a limit switch is hit, if using Mach, then the RESET on your monitor will start blinking and the operation stops.

Estop is a must. It runs through the power supply for a quick shut down. On my setup don't confuse the estop on the breakout board (that we just talked about) with the manual estop located on the sides of my CNC. I've hit that rascal many times before I broke a bit or ran the darn gantry off the end of the machine. There is no way to shut your machine down quick enough when searching for your curser on your monitor.
Put one on both sides of your CNC. Once your learn your machine you'll avoid many errors, but you still will use the EStop from time to time.

Bob Campbell CNC designs has a schematic of how to wire the powersupply for the ESTop and limit switches. < www.Campbelldesigns.com>

I may have misnterpeted the diagrams and wired mine all wrong but it works!
I too, was a noovice in powersupplies. Be careful. A powersupply will kill you!

Your best money would be to buy a powersupply from Bob Campbell ready to go. It will have the right size transformer, caps, drivers, breakout board that you will need.

Good luck.

Originally Posted by drafterman I am very new to the whole scene, but during my reading I see very little discussion about home/limit switches or e-stop buttons. Does not everyone use these? I also have read that the interface wiring of limit switches to motor driver boards can be tricky so as not to damage the drivers. Any schematics or advise would be appreciated. I am going to use xylotex boards with my stepper motors. Also, on the z-axis for plasma torch height (non digital controlled)...how do you set your zero height? Do you just design in enough over travel in the axis that the transfer balls allow for this?

[skiddaw]

A dead microwave oven will get you up to three microswitches a couple of relays and two magnets for your next wind generator project.