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Question about micro switches and emergency stops

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  • Question about micro switches and emergency stops

    I have a question about micro switches and emergency stop switches. The picture below is of the two micro switches that start my lathe (one for forward, one for reverse).

    The cheesy plastic cover that was guarding them let a lot of chips and oil in and they don't work anymore. I'm looking for a better quality replacement and I found some at McMaster-Carr that I think might work, but I'm electrically challenged (parts 7090K41 and 7090K51 at I know they would fit in the space and have the same mounting hole locations, but will they work electrically?

    Likewise, the emergency stop button doesn't work (it actually broke in half). I couldn't get a good picture of that switch, but the only markings on it are "Ui 660V Ith 10A". The selection at McMaster-Carr ( is pretty small, so I'm guessing there's not a whole lot of variance among e-stops? The one on the machine has four terminals (2 circuits?), but only two are being used. Do I need a DPST switch, or would a SPST do the job in this case? Are there any other good places to look for these things besides McMaster? I don't mind paying a bit more for quality, so any and all recommendations would be appreciated.

    Thanks in advance!
    Stuart de Haro

  • #2
    I think McMaster switches are OK/
    ebay has same part#

    Much cheaper.



    • #3
      well more information plz

      They aren't that expensive so buy a couple of them. Even the expensive ones break. The micro switches you are looking at SHOULD work for you, but the motor size and voltage would really help. Wiring diagram is a plus.

      Stop button. There are a whole mess of them. Basically you might have a Normaly close (n/c) and/or Normaly open (n/o) on your stop button. A wiring diagram would help (yes again). Up here the stop buttons are measured in mm's for the mushroom (red part) and the holes where they go in are usually standard.



      • #4
        This looks like a disaster about to happen.
        You need to enclose the switch to keep the metal and "crud" out if the switch and off electrical terminals. If you move down the McMaster Carr page, there are several enclosures shown. In addition, if one of those doesn't suit you. there are still others sold by other suppliers.
        It is your project, not mine, but I wouldn't operate the machine without a cover around the switch.


        • #5
          The motor is 1.5hp single phase, 220v. Here are scans of the wiring diagrams.

          JCD, as I mentioned in my original post, the switches don't work. They are not connected to electricity, and they WERE covered by an enclosure that let all that stuff in there. You don't need to tell me that part of the lathe needs to be improved. I'm planning on making a much better box for them.
          Stuart de Haro


          • #6
            The E-stop switch should be 2-pole (meaning 2 "circuits"), latching and handle the maximum voltage and current your machine uses or above and it should be N/C (normally closed).

            And it should be wired first in the circuit so that when you hit it, it cuts all power from the machine, meaning it disconnects live AND neutral wires. This is done so that if any idiot connects live & neutral at some point in the grid vice-versa to what they should (as some countries have polarised plugs), it makes sure that there is no voltage in the machine.
            Amount of experience is in direct proportion to the value of broken equipment.


            • #7
              Use these Honeywell sealed switches with flying lead.Very common on cnc machine tools and very reliable.

              For an e-stop button the usual contact block is NC (normally closed).It is usual to buy buttons by picking the size and type of actuator (button,toggle,key etc)
              then the contact type and number required.NC or NO.
              It is usual for the e-stop to cut the control circuit,not the incoming mains.Most modern machines have an e-stop relay/contactor and the e-stop button would be
              part of the string controlling that relay/contactor.Otherthings such as overtravel limit switches,lube pressure/level may also be part of the string if so desired by the machine builder.
              Last edited by Mark McGrath; 03-20-2012, 07:36 AM.


              • #8
                The LXW5 is a standard Micro Switch part number. I would avoid the eBay switches as they are chicom clones. You can check with McM, but their switches should be Micro/Honeywell, and should be better quality.

                The E-stop switch is also probably a clone of a common switch. If you have any commercial electrical supply houses local to you, they should be able to supply you with the Micro switches as well as a suitable replacement for the E-stop switch. They will also have proper enclosures available.
                Jim H.


                • #9
                  You need to enclose the switch in a sealed housing and use a short rod that extends into the housing to actuate the switch. Use a close but not tight fitting o-ring that the actuator rod will slide through. Make the part of the actuator rod inside larger than the hole so it cannot pass through the hole. That will also prevent oil from migrating to the actual switch. This is not hard to do at all but if you don't it will fail again.

                  If it needs the rolling action you can use a small chunk of Teflon to make a shoe for the end of the rod. In most cases you can just round over the end of the rod and it will work fine. Use aluminum or plastic for the actuator rod so it doesn't attract swarf magnetically. You may need to add a small spring to make for positive actuation. If you check the specs on the micro switches there are different specs for the amount of spring force required to operate the switch. Pick one that takes a good amount of force for positive actuation/deactuation.

                  Another spec is the amount of hysteresis that the switch has. That is the difference in travel between on vs off. If it is just an on/off switch hysteresis doesn't matter. For a CNC limit switch it makes a difference in some cases.
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                  • #10
                    Why are you guys getting so uber involved with this? The microswitches only energize either the forward or reverse contactor. He said there was a cheesy cover over the original switches, and how long did that set last. Hell, for no more than they cost, microswitches are all but sacrificial.

                    Throw in another set and turn that puppy on.


                    • #11
                      It could be a Bad Thing if it turns on when it shouldn't.
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                      • #12
                        I suspect that the contactors have 24V a.c. coils - a quick way to check would be to look in the electricals box (usually on the back of the headstock) for a transformer (possibly what they've labelled TC in the very poor wiring diagram). If there's one in there, yep, 24V control circuit, so any similar microswitch will do, it'll only be switching around a quarter of an Amp. - it would be a good idea to put some sort of enclosure around it, the worst-case is a short closing both the contactors K2 and K3 (motor run fwd and reverse) at the same time, which would blow fuses, if nothing else...

                        The EStop is likely to be S1 in the 24V control circuit, along with the microswitches for the changewheel/belt cover and the chuckguard (if fitted) - these are probably S3, S4, S5 - one will be a "stop"/"power off" button, I'd guess, and S2 would be the "start"/"power on" button? These would operate the K1 contactor to apply power to the rest of the control circuit.

                        I have to say that's one of the worst diagrams I've ever seen - Chinese lathe, by any chance?

                        Dave H. (the other one)
                        Rules are for the obedience of fools, and the guidance of wise men.

                        Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools


                        • #13
                          I don`t see anything wrong with the electrical drawing.Appears to be European or at least to European specs.
                          TC is the control transformer and the forward/reverse contactors will be mechanically interlocked plus it`s usual to feed the coil of the forward contactor through a NC auxillary contact on the reverse contactor and the coil of the reverse contactor through a NC auxillary contact on the forward contactor.


                          • #14
                            Yes the schematic shows NC opposite coil interlock contact, there should also be mechanical interlock.
                            One problem with using AC magnetic devices, contactors, solenoids etc, if the armature does not move over when it should, or someone forces a solenoid over that is picked up, it is usually instant burn out, doesn't happen with DC coils.