Remote Control Cutoff for CNC Equipment

Ideas for solving a unique problem: shutting off a CNC router while programming and observing the machine remotely. August 21, 2006

How could I wire my safety mats so that I can stop my router from 180 ft. away while I watch it on a closed circuit monitor?

Forum Responses
(CNC Forum)
From contributor V
I wouldn't wire my safety mats so you can stop your router from any distance.

From contributor M:
The intent of the mats is to stop the machine in the event that an operator or passer-by inadvertently gets too close to the operating section of the equipment. This is very sound, rational safety procedure. I do not understand the why would want to stop the machine from a remote location. Please give some more information and there may be another way of trying to accomplish what you want.

From contributor W:
You don't actually have to wire it to the safety mats. You could have a simple switch like your emergency switch that is run to the safety relay in your CNC.

From contributor Z:
I recently purchased a four button industrial garage door opener and receiver that I added to one of my customer's machines. The receiver has four outputs that can be wired normally open or normally closed. The output voltage on each one of the four outputs matched the control voltage of the machine. Here is how I wired the system:

Button #1= Emergency Stop
Button #2= Feed Hold
Button #3= Cycle Start
Button #4= Reset

I purchased the unit from an industrial electronics supply company for about $90 and so far it works great. It only took me about 45 minutes to wire it up and other than a limited range, it is awesome. The usable range could be extended simply by adding a long wire to the receiver's antenna.

From contributor M:
Some routers have features which keep the vacuum engaged during shutdown or loss of power to a circuit; some do not. My concern would be shutting down via the remote switch while the spindle is cutting, if this is a machine that does not have protocol to maintain vacuum in that state - part is being engaged at 18,000 or so rpm with *no* hold-down method! This could sling a sheet not feet, but yards, at high velocity.

You could have the best of intentions, but there may be other considerations which you have to know if you intend to modify safety devices in any way. You owe it to yourself for legal and liability protection and more importantly, you owe it to the employees that are effected and their respective families who loan you their mothers, fathers, sons, daughters to *make sure* you are not taking any risks with their safety. I am sure the original poster has a specific intent, but there may be a more viable method of achieving what he wants without even running the risk of compromising safety.

From contributor W:
I have hit my emergency stop many times on our CNC while cutting and have never had a piece fly off the pods. I'm sure it takes longer for the vacuum pressure to drop than a tool to go from 18000-0rpm while in the wood.

From contributor M:
That is with your machine, your vacuum, your router spindle. We do not know what the questioner has. It could be a 1985 model with a Shop Vac machining aluminum. When you hit the E-stop, you had the advantage of being at the machine, weighing the alternatives, assessing the situation and making the best decision at the time, drawing from all your senses. If I were to install a switch on your car where I could place it into neutral or apply the parking brake remotely, those two independent acts, in themselves, may not cause you to wreck. However, the act of me doing it unexpectedly while you are driving may cause you to react in a manner that causes you to wreck.

Too many variables here for me to bless this, sorry. I respect everyone's initiative and knowledge on this forum, but quite frankly this is something that rightfully deserves long and hard consideration prior to implementing.

From contributor W:
I do agree that we need more info, but I can remember one time on the AXYZ I used to run with no vacuum, I forgot to tighten the clamps to hold down the 4'x8'x.25" aluminum sheet. I cut the whole sheet of 12" high letters and the sheet barely moved, so even if it's a 1985 with a Shop Vac, I still don't see that being a problem.

From the original questioner:
When I step on the safety mats, the spindle stops. My new office is 160 to 180 feet away, downstairs, and we don't have an operator.

From contributor S:
My 20 year old son runs our machine, so I asked him what he would do to be able to stop the machine from further away. He wondered if you could install the same type of mat in your office that is connected to your machine. If there is a problem, just step on the mat, but in your office. He figures you need some wire and a small section of mat.

From contributor Z:
It sounds like when your mat is stepped on, your machine just goes into a hold state and nothing else happens until you get off the mat and tell the machine to resume. If this is correct, then most likely your mats are wired on a normally closed circuit and your restart button is a momentary switch that reengages the contacts on the safety mat. If you are unable to find a remote control with a receiver that matches the control voltage on your machine, you could easily buy some 2 pole shielded cable (2 lengths of 180') and a couple of push buttons and just add two switches in your office. Having the ability to remotely stop your machine from a distance should not pose any safety issues and if the restart button is wired correctly, you would not be able to restart the machine after remotely stopping it if someone was standing on the safety mats at the machine.

From contributor E:
Check with your machine manufacturer, but on my 3 axis, there is a slot on the control board where we can wire in an emergency stop switch. It could be hard wired the distance you're talking about. I have the option of using a normally closed or open switch. It can be set up in the software.

From contributor I:
I am a little hesitant about giving electrical wiring advice without seeing a wiring schematic, but here goes. I would suggest inserting a relay/contactor in series (not parallel) with the emergency button. The switch in your office would energize the relay/contactor and open the circuit. You could also wire in an indicator lamp at the machine, to show that your office switch is activated. The reason I did not mention the mat is because I do not know how it sends a signal to the controller or PLC.

From contributor L:
The easiest method would be - provided your machine has a hand held remote with an emergency stop button - to extend the length of the cable. This would give you the ability to control feed as well as stopping the machine. Also check to see if your control picks up at the same line of code and continues on or if it has to start all over when E stop is pushed. This could be a real hassle in 5 axis machining if not. Another possibility is to have the machine connected to the internet, connect to the machine through its IP address using Netmeeting and access the monitor and you may be able to hit the stop button with your mouse when needed.