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IndustryArena Forum > Manufacturing Processes > Safety Zone > Wiring Limit, Home and E-Stop Switches
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  1. #1

    Wiring Limit, Home and E-Stop Switches

    I found this diagram, mentioned in an old thread, that seems to be a good way to wire up limit, home and E-Stop switches.

    My question, is if I can just put the E-Stop switch in series with the limit switches and free up a parallel port input? I assume so.

    Also, should the home switches be in the same location as X--, Y-- and Z++ limit switches or offset from each other?

    I am using Mach3, if that matters.
    Attached Thumbnails Attached Thumbnails Switch_wiring_3.png  

  2. #2
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    Hi Race man!

    NO! Wire the Estop to its own separate input.

    If you want to save inputs, just wire ALL of the switches NC in one big series loop, connect one end to PSU ground and the other end to one input. Mach3 knows what switch is what. You can use 3 of the switches as both home and limit switches.

    CR.
    http://crevicereamer.com
    Too many PMs. Email me to my name plus At A O L dot com.

  3. #3
    Quote Originally Posted by Crevice Reamer View Post
    NO! Wire the Estop to its own separate input.
    OK. Help me understand the reasoning behind that.

    Quote Originally Posted by Crevice Reamer View Post
    If you want to save inputs, just wire ALL of the switches NC in one big series loop, connect one end to PSU ground and the other end to one input. Mach3 knows what switch is what. You can use 3 of the switches as both home and limit switches.
    I guess that I wanted to leave one free for some future use.

    I know that 3 of the switches can be used as both limit and home switches with Mach3, but I assume that you cannot wire them in series to do so. Seems that I can put the X++, Y++ and Z-- switches in series and tie those to one parallel port input, but leave the combo home/limit switches as separate inputs.

  4. #4
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    Nope! Wire all six Normally Closed switches in series and forget about it. Three of them will also be combo. Mach3 will know which switch is which and for what.

    CR.
    http://crevicereamer.com
    Too many PMs. Email me to my name plus At A O L dot com.

  5. #5
    Quote Originally Posted by Crevice Reamer View Post
    Nope! Wire all six Normally Closed switches in series and forget about it. Three of them will also be combo. Mach3 will know which switch is which and for what.
    I guess that I am having a hard time grasping that. If all 6 limit switches are wired to the same parallel port pin, how does Mach3 really know it is in the home position and not at some other limit?

    I'm a noob to Mach3 and CNC in general, so it helps if I have a little more explanation of things for me to understand. I just got my first CNC machine this past week.

  6. #6
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    Mach3 knows where all the switches are. During a cutting operation, if it encounters a switch, it assumes it to be a limit and shuts down. During homing, it first moves the Z until encountering a switch, recognizes home, and backs off a trifle to close the switch. Then it will home the X, and then the Y. Because limits and homes are used in two completely separate operations, it has no trouble doing this.

    Limit/home/Estop switches use very low Voltages and are easily subject to crosstalk from other wires nearby. You MUST use shielded wire and try to route it not close to other wires.

    Combining Estop with the homes/limits just multiplies the chances of having spurious signals interupting your CNC program.

    You may find some of this info to be helpful:

    http://crevicereamer.com/Page_2.html

    CR.
    http://crevicereamer.com
    Too many PMs. Email me to my name plus At A O L dot com.

  7. #7
    OK, I believe that I understand now. So, I can simplify that diagram and just use two parallel port inputs. One for E-Stop and the other for all of the limit switches in series (3 of those doing double duty as home switches).

    Can I get the +5V off of one of the other parallel port pins?

  8. #8
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    That is correct about the switches. Regarding the 5v, I believe you want to keep the power on the pc side seperate from the machine sides power. A cheap wall wart will supply the 5v (most cell phone chargers are 5v, check first). You could try the 5v from the PP and if it starts throwing faults get power elsewhere. I have had many problems with grounds and such. Nothing causing any release of the magic smoke but tripping estops and such. In fact it has happened every time I have added something new and electrical in the system, such as probes, relays and limit switches. Good luck and enjoy. Btw when you see it home the first time it is too cool. It works exactly like CR said.
    Quote Originally Posted by gpraceman View Post
    OK, I believe that I understand now. So, I can simplify that diagram and just use two parallel port inputs. One for E-Stop and the other for all of the limit switches in series (3 of those doing double duty as home switches).

    Can I get the +5V off of one of the other parallel port pins?

  9. #9
    Quote Originally Posted by Fastest1 View Post
    Regarding the 5v, I believe you want to keep the power on the pc side seperate from the machine sides power. A cheap wall wart will supply the 5v (most cell phone chargers are 5v, check first). You could try the 5v from the PP and if it starts throwing faults get power elsewhere.
    I was hoping to avoid yet another external wire to deal with. So far, it seems I have a spaghetti factory going on and haven't yet added the limit switches or the E-Stop, which will add to it. If I can get that +5V off the parallel port, is there a specific pin or is there something that I need to do in Mach3 to turn on an output pin?

    Quote Originally Posted by Crevice Reamer View Post
    You MUST use shielded wire and try to route it not close to other wires.
    I guess that precludes bundling them with stepper motor wires, even if using shielded wire, correct?

  10. #10
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    Quote Originally Posted by gpraceman View Post
    I was hoping to avoid yet another external wire to deal with. So far, it seems I have a spaghetti factory going on and haven't yet added the limit switches or the E-Stop, which will add to it. If I can get that +5V off the parallel port, is there a specific pin or is there something that I need to do in Mach3 to turn on an output pin?
    Ah, how simple life becomes when you use a G540 and avoid all of this spaghetti.

    I guess that precludes bundling them with stepper motor wires, even if using shielded wire, correct?
    YES, if motor wires are unshielded, Not necessarily if motor wires ARE shielded. Either way, the drain wire of the shielding must be grounded at the BOB end only.

    CR.
    http://crevicereamer.com
    Too many PMs. Email me to my name plus At A O L dot com.

  11. #11
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    Now, if you want to cut down some of the wiring complexity:

    I don't USE limit switches with steppers. IMO they are unnecessary. Worst case if you exceed a limit, steppers will just stall harmlessly. Soft limits set in Mach3 work just fine to prevent this though.

    I consider HOME switches to be mandatory though.

    CR.
    http://crevicereamer.com
    Too many PMs. Email me to my name plus At A O L dot com.

  12. #12
    Quote Originally Posted by Crevice Reamer View Post
    Ah, how simple life becomes when you use a G540 and avoid all of this spaghetti.
    That is a very nice controller and something that I considered. I'm not sure that I would have less of a spaghetti issue with it though. I went with the control box that Zenbot offered. Most of the spaghetti is actually all of the cords and cables for the computer and monitor that I am using. I was considering a SmoothStepper so I could use my laptop, but thought that I'd give the desktop a try. I had a recently retired XP machine within easy reach.

    Quote Originally Posted by Crevice Reamer View Post
    I don't USE limit switches with steppers. IMO they are unnecessary. Worst case if you exceed a limit, steppers will just stall harmlessly. Soft limits set in Mach3 work just fine to prevent this though.

    I consider HOME switches to be mandatory though.
    I appreciate all of your assistance. I guess I'm a bit paranoid of messing up the machine as I am learning to use it. I'll just worry about the home switches, make sure the wires are shielded and not run them with the stepper motor wires.

    Do I really even need to worry about an E-Stop?

    I do have some soft limits set in Mach3, at least for X and Y (until I get the replacement for the Z head that was damaged during shipment).

  13. #13
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    Quote Originally Posted by Crevice Reamer View Post
    Mach3 knows where all the switches are. During a cutting operation, if it encounters a switch, it assumes it to be a limit and shuts down. During homing, it first moves the Z until encountering a switch, recognizes home, and backs off a trifle to close the switch. Then it will home the X, and then the Y. Because limits and homes are used in two completely separate operations, it has no trouble doing this.
    CR.
    Plan on using EMC2 when I finally get my "new" mill up to speed. Does EMC2 also know where all the switches are?

    Thanks

    Tom

  14. #14
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    Quote Originally Posted by gpraceman View Post
    Do I really even need to worry about an E-Stop?
    That big red mushroom switch is the last chance panic button. IF you are there, and you see that everything is going south, a push of the Estop should stop all axis movement.

    If you have the spindle controlled through Mach3, Estop will also halt that.

    I personally, like to HAVE that Emergency Stop button handy.

    THT: I cannot answer anything about EMC2. I'm a Mach man.

    CR.
    http://crevicereamer.com
    Too many PMs. Email me to my name plus At A O L dot com.

  15. #15
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    Quote Originally Posted by Crevice Reamer View Post
    THT: I cannot answer anything about EMC2. I'm a Mach man.
    CR.
    Thanks.

    I bought the Sherline CNC kit (lathe and mill) which came with EMC2. And we've spent millions in tax money developing EMC, only to have a bunch of open source guys finally make it work.

    But since I've got EMC2 running on one machine, it makes perfect sense to me to put EMC2 on the the third machine.

    Sherline doesn't have any limit switches, or a big red eStop switch, so I can't just follow their lead.

    Tom

  16. #16
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    No Estop on EMC2? What do you do when everything is going wrong? Pull the power cord? If no estop is available I am not sure it would be safe.
    Quote Originally Posted by TarHeelTom View Post
    Thanks.

    I bought the Sherline CNC kit (lathe and mill) which came with EMC2. And we've spent millions in tax money developing EMC, only to have a bunch of open source guys finally make it work.

    But since I've got EMC2 running on one machine, it makes perfect sense to me to put EMC2 on the the third machine.

    Sherline doesn't have any limit switches, or a big red eStop switch, so I can't just follow their lead.

    Tom

  17. #17
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    Quote Originally Posted by Fastest1 View Post
    No Estop on EMC2? What do you do when everything is going wrong? Pull the power cord? If no estop is available I am not sure it would be safe.
    There is a power switch on the controller box, and a power switch on the spindle motor, and a power switch on the outlet strip everything is plugged into. This is apparently adequate for a small benchtop machine. For instance, the mechanical travel stops will stall the steppers on a Sherline.

    The same would not be adequate for a larger mill. The Bridgeport I'm currently reworking had an eStop button with the original BOSS computer, and will have the same eStop button, at a minimum, after I finish configuring it to run on a PC. In addition, power to the computer and drivers comes through an air conditioning contactor, and power to the VFD for the spindle comes through a second air conditioning contactor. I've got a convenient wall switch which will kill the 24 volts to the contactors, which will make the mill get real quiet, real quick.

    Tom

  18. #18
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    I was scared you were going to say that. Though i do understand these benchtop machines are smaller and theoretically less dangerous. I dont think that is the best way to approach safety. In fact if it was mine, something (A BIG RED BUTTON) would be wired to the relay or contactor that killed power to all 3. Kind of like your pulling the power just safer and more obvious. Me being only a hobby machinist and not trained might be where my ignorance comes in but at times I freeze in absolute disbelief when the cutter starts going the wrong way after 4000 correct lines or so. At those moments the Estop is never close enough. In fact I am still trying to figure out how guys in the youtube videos never have torn up clamps LOL. Anyway I know the machines can take stalling as I have done about everything wrong you can do with a Sherline and it still works! I am sure if it was a BP or such it would be broken, or the table would have milling grooves, or drill marks, or a broken screw, the list would go on!
    Quote Originally Posted by TarHeelTom View Post
    There is a power switch on the controller box, and a power switch on the spindle motor, and a power switch on the outlet strip everything is plugged into. This is apparently adequate for a small benchtop machine. For instance, the mechanical travel stops will stall the steppers on a Sherline.

    The same would not be adequate for a larger mill. The Bridgeport I'm currently reworking had an eStop button with the original BOSS computer, and will have the same eStop button, at a minimum, after I finish configuring it to run on a PC. In addition, power to the computer and drivers comes through an air conditioning contactor, and power to the VFD for the spindle comes through a second air conditioning contactor. I've got a convenient wall switch which will kill the 24 volts to the contactors, which will make the mill get real quiet, real quick.

    Tom

  19. #19
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    Quote Originally Posted by Fastest1 View Post
    I was scared you were going to say that. Though i do understand these benchtop machines are smaller and theoretically less dangerous. I dont think that is the best way to approach safety. In fact if it was mine, something (A BIG RED BUTTON) would be wired to the relay or contactor that killed power to all 3. Kind of like your pulling the power just safer and more obvious. Me being only a hobby machinist and not trained might be where my ignorance comes in but at times I freeze in absolute disbelief when the cutter starts going the wrong way after 4000 correct lines or so. At those moments the Estop is never close enough. In fact I am still trying to figure out how guys in the youtube videos never have torn up clamps LOL. Anyway I know the machines can take stalling as I have done about everything wrong you can do with a Sherline and it still works! I am sure if it was a BP or such it would be broken, or the table would have milling grooves, or drill marks, or a broken screw, the list would go on!
    Well, there is an eStop button on the screen with EMC2, and of course the escape key works as an eStop button also. But since I didn't design and build the Sherline, I can't take responsibility for their design.

    But both my Sherline mill, and my BP have some minor gouges in the table. Those on the Sherline were not caused by being out of control, and the ones on the BP got there in its previous life in a commercial shop, so can't comment on how they got there, as I just don't know.

    But, I do spend a fair amount of time running simulations before I actually power up the mill itself. And I'm still looking for a nice rubber pencil or such that I can use as a cutter simulator so that I can actually run the steppers and watch the cutter path in real life before starting to spin the spindle.

    And, knock on wood, I've not yet broken an end mill, and I've worn out several of them.

    Tom

  20. #20
    I have one last question on the E-Stop. Should the E-Stop be connected to the driver board as well as the parallel port, to tell both the hardware and the software to stop things? The E-Stop buttons that I have seen look to have two sets of terminals. I don't know if these are electrically isolated from each other, since my driver board is working off 24VDC and the parallel port uses 5VDC and those shouldn't mix.

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