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Setting up safe limit switches
« on: December 09, 2010, 09:45:49 PM »
Hi all  I am a new user to Mach3 and have built a homemade 3 axis CNC router. I would like to set up limit switches in case somthing goes wrong.
My question! micro switches have a common and a NO and NC terminal. I am using a TB6560 driver .
Where do I place the wires to me if I have the 5v wire as common where does the ground wire connect as I do not want a dead short between the two.?
Keep it as simple in plain language please.
Jim ???

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Re: Setting up safe limit switches
« Reply #2 on: December 10, 2010, 05:20:30 AM »
Use the N/C side then if a wire breaks it stops the machine instead of only finding out when the machine crashes through the limits.

I've only got homing switches and they are in series, mach can sort out the homing order and only looks for the trigger for the axis it's homing at the time.
So you should be able to put all your limits in series and set one as home or have seperate home switches if that's how you want it.

I just home each time the machine is switched on and make sure the soft limits are on, this seems to take care of everything for me BUT my mill is only smallish and not very fast, same with my router.

Re: Setting up safe limit switches
« Reply #3 on: December 10, 2010, 04:51:59 PM »
Thanks Jeff and Steve
Still clear as mud.
When I look at the wiring diagrame if shows GND as common and the NC OR NO as the switch. So I assume the controller terminal goes low and activates the axis stop.
I will check it out in greator depth at a later date, I am only runing very slow at the moment and doing test cuts to see what accuracy I am getting.
Re: Setting up safe limit switches
« Reply #4 on: December 11, 2010, 09:59:25 PM »
1 ) Mount the switches. You may want to wire them before mounting them. Choose the wiring path carefully.

2 ) Connect the three home limit switches in series (X-NC to Y-C, Y-NC to Z-C) using the switch common (C) and the switch normally closed contact (NC).

3 ) The remaining X-C and Z-NC terminals will be wired to the input port. Nothing will be connected to the normally open (NO) contacts.

If you have a multimeter, use the ohms or continuity setting, test each switch and the three switches wired in series. The two wires coming from the switches to the port should appear shorted until you press any of the three switches. Then they should indicate an open.

4 ) Wire the switch X-C wire to the port ground.

5 ) Wire the switch Z-NC switch wire to one of the inputs. The input should be set-up for stopping all three axe (X, Y, & Z) with a positive signal.

6 ) Now get a 4,700 ohm (1/8 watt or 1/4watt) resistor. Any resistor value from 500 ohms to 20,000 ohms will work just fine. Lower ohms draws more current, and higher ohms allows more sensitivity to noise. If you need to buy one fast, Radio Shack has them locally for under $2. for a set of 5.

7) Connect the resistor between the switch input port (Z-NC) and the Plus 5 volt supply.

8 ) Monitor the port on the diagnostic screen, it should indicate that the port is at ground. When you activate any of the switches, it should go to plus 5 Volts and turn on the port indicator, as well as E-stop the machine.  

9 ) If any of the daisy-chained switches or any of the wires are defective, the circuit will open and do an E-Stop.

10 ) Set the software de-bounce timing so that the switches do not trip under normal use from vibration. (try 200 & 100)

Hope this helps,
Re: Setting up safe limit switches
« Reply #5 on: December 12, 2010, 10:03:42 PM »
Thanks Bill
Now it all makes sense.
Regards Jim
Re: Setting up safe limit switches
« Reply #6 on: December 12, 2010, 11:12:59 PM »
I forgot two things.
1) Your driver board may not need the resistor (mine requires it). The photo of the board appears to show that the inputs are optically isolated, this means that the resistor is probably built in. You can check this by checking the voltage on the input pin with respect to the ground pin. If it reads above 4 Volts it is in there. If you add one anyway, it should not hurt anything. (Another clue that it is in there is that the connector diagram does not show a plus 5Volts available on it for connection).

2) On the Settings screen, turn ON "Auto Limit OverRide". This allows you to reset the E-stop and move off of the limit switch with manual motion control (arrow keys). 

Good luck,