[gpraceman]

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.

[Crevice Reamer]

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.

[gpraceman]

NO! Wire the Estop to its own separate input.

OK. Help me understand the reasoning behind that.

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.

[Crevice Reamer]

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.

[gpraceman]

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.

[Crevice Reamer]

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.

[gpraceman]

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?

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?

[Crevice Reamer]

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.

[gpraceman]

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.

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).

[Crevice Reamer]

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.

[TarHeelTom]

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

[gpraceman]

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?

[Fastest1]

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.

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?

[Crevice Reamer]

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.

[gpraceman]

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.

[TarHeelTom]

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.

There's probably no one right answer to your question. However, seems like that interrupting the 24V supply to your driver board, you remove the power supply to the steppers or servos.

My BOB has a 120V input, so I could interrupt that. But it also has a dedicated eStop terminal, which must be grounded to enable the BOB.

I would assume that the fact that there are four terminals on your eStop switch, there are probably two isolated sets of contacts. But this is easy enough to check with an ohmmeter or a battery and bulb, or test light, or whatever you have available. But DO check first.

There do exist devices which have multiple terminals available for a single point of contact. For instance, the AC contactors I use to power my mill have a minimum of three, and sometimes more connections available for each terminal. This is handy, as I run a piece of #12 wire to the clamp screws on the power in and power out terminals on each circuit, then have additional spade lugs available for running, for instance, a #18 wire to an indicator lite for that circuit.

Tom

[gpraceman]

Tom,

I haven't purchased an E-Stop switch yet. I just have been looking at several on the web and eBay.

I don't have a BOB but my driver board does have a terminal for the unused parallel port pins. Separate from the parallel port, it also has one terminal for each set of axis limit switches. I was not intending to use those, since I wouldn't be able to jog off of the limit switches. I was wondering, though, if I could wire the E-Stop to those. Either that or just switch the incoming power.

This is the driver board that I have. http://www.easy-cnc.com/3axisdriver.html

I guess my question is if it is preferable to have both the software and hardware stop when the E-Stop is hit or if stopping just the hardware is sufficient.

[TarHeelTom]

Tom,

I don't have a BOB but my driver board does have a terminal for the unused parallel port pins. Separate from the parallel port, it also has one terminal for each set of axis limit switches. I was not intending to use those, since I wouldn't be able to jog off of the limit switches. I was wondering, though, if I could wire the E-Stop to those. Either that or just switch the incoming power.

I guess my question is if it is preferable to have both the software and hardware stop when the E-Stop is hit or if stopping just the hardware is sufficient.

Don't know why you can't jog off the limit switches. If you use only one pin for all of the limit switches, for instance, three NC limit switches in series, to break continuity to the pin, but with a separate push button to override the limit switch as you jog back.

It would be nice (is it possible?) to use an input pin to tell the software that the eStop has been triggered. Certainly it's possible to send the eStop signal to the pin. Have no idea if either Mach3 or EMC2 will recognize that software. That quote seems to indicate that Mach3 will recognize the eStop input.

Remember that even if you tell the software that you've hit eStop, the software has no way of knowing where the steppers are NOW, as they coasted to a stop. Which means you've got to rezero all the axes.

Basically speaking (and I've not ever used Mach3) you have a configuration table which you use to tell Mach3 or EMC2 what function each pin has, and whether it's a positive or negative input.

Although the capacitors can keep running the motors for a while if you switch the AC to the power supply, cutting the DC supply FROM the power supply would result in nearly an instant stopping of the motors, after the normal slowdown time.

Tom

[gpraceman]

Don't know why you can't jog off the limit switches. If you use only one pin for all of the limit switches, for instance, three NC limit switches in series, to break continuity to the pin, but with a separate push button to override the limit switch as you jog back.

The driver board manual does say that you have to move off the switch to re-enable the axis, if using the board's limit switch inputs.

It would be nice (is it possible?) to use an input pin to tell the software that the eStop has been triggered. Certainly it's possible to send the eStop signal to the pin. Have no idea if either Mach3 or EMC2 will recognize that software. That quote seems to indicate that Mach3 will recognize the eStop input.

Seems quite possible. I just am not sure how to wire things up to let both the driver board and the software know that an E-Stop has been hit. The driver board operates off of a higher voltage that the parallel port, so it doesn't seem straight forward.

Remember that even if you tell the software that you've hit eStop, the software has no way of knowing where the steppers are NOW, as they coasted to a stop. Which means you've got to rezero all the axes.

That seems to be a given as the Mach3 manual also states

It will not generally be possible to continue machining a part after an EStop but you and the machine will at least be safe.

[TarHeelTom]

Seems quite possible. I just am not sure how to wire things up to let both the driver board and the software know that an E-Stop has been hit. The driver board operates off of a higher voltage that the parallel port, so it doesn't seem straight forward.

You've got 24V available. One easy way is to use the contacts on a very small 24V relay to tell the pin that things are normal. You power the coil routinely with the 24V line to the driver board. Use the NC eStop switch to interrupt the 24V to the driver board and the relay coil, which either opens or closes the relay contacts to send your message to the input pin to the computer.

Actually, you could use either a relay with multiple contacts, or multiple relays to send the same signal to other receptors, as needed. One might be spindle power. In my case, I'll use some contacts, relay or switch, to break the common return line from the run contacts on the VFD. VFD's don't like to have any contacts between the VFD and the motor.

Another simple method to send the message to the pin would be an opto-isolator. These are very simple chips, and are readily available. My BOB has an opto-isolator on the board for every pin, except for the pins feeding the geckos, which have their own built-in opto-isolators.

As an aside, this is a benefit of buying a slighly more expensive BOB, as it has more features, such as relays and opto-isolators already installed on the board, making the installation of lines for other purposes so much easier and simpler.