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limit switches work and dont work i need help
« on: November 11, 2012, 05:14:28 PM »
I bought a cnc router parts 4x4 machine.  I added proximity switches to the xyz axis (USED FOR HOMING AND LIMITS THE SAME SWITCH).  I keep on getting an intermittent limit switch alarm on the z axis than the y acts up.  Mach 3 is the only system running while the machine is on.  I play with the machine for about 30mins and than it works the rest of the day.(turn the machine and computers on and off,turn the limit switches off)  I also tried to separate the motor wires from the limit switches wires.   I NEED HELP

Keith
« Last Edit: November 11, 2012, 05:18:34 PM by drivetrain2 »

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Re: limit switches work and dont work i need help
« Reply #1 on: November 11, 2012, 08:07:32 PM »
Keith,
   Have they ever worked successfully and then there was a change?
   The intermittent problem has always existed?
   What kind of controller are you using?
   Power supply?
   Are you running any debounce?
   Capacitors?
   EMI filters?
   Do you have a "star ground"?
   Is the V- of your power supply tied a point on the chassis also or just to the - terminal of your controller?
   These are a few things to check first.
  For me the V- not being tied to a star ground was the issue. Nothing else helped. It didnt seem safe with my limited electronics experience but with the help of others here. It runs great.
  Also pictures of your electronics are always fun and helpful. Nothing fancy, a cell phone will do a great job.   
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)
Re: limit switches work and dont work i need help
« Reply #2 on: November 13, 2012, 06:29:31 PM »
no (off and on) but when it works it works till i start it up again
yes
pmdx-126
where would it be in the controll box
not sure what debounce is
not sure
there is a emi filter on the plug to the control box
the box has a ground inside for the control box...
the kit is a cnc router parts nema  34 built by them
 can you pm me with info and i will send pics from my phone
thanks keith

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Re: limit switches work and dont work i need help
« Reply #3 on: November 13, 2012, 07:37:27 PM »
no (off and on) but when it works it works till i start it up again
Well that isnt helping me so maybe someone else will chime in however ground loops and such can be very hard to track. So we will keep looking.  

yes
This makes me think it is most likely something that was never connected, designed or implemented correctly.

pmdx-126
Good board, lots of great features. Is powered by 120/240. It is the one I am running currently on my G0704.

where would it be in the controll box
The PMDX 126 has wires running to the drivers for each axis, the power supply will be feeding those drivers only, as the PMDX gets it power from the mains. There will be wires going from the drivers to the steppers also. The terminals on the drivers are most likely marked with a - & + symbol for the input voltage. Most hobby level machines are running 24-48vdc power supplies with a few running higher.

not sure what debounce is
Debounce is a setting on the "general config" page of Mach 3. There are 2 settings. You only need to concern yourself with the 1 marked "debounce interval" this setting is the amount of time (40us) a signal has to be present before Mach recognizes it. This is a software work around for systems with electrical noise present. Small numbers of 100-500 are acceptable and will help many machines. Many people cant get away with 0 levels for some reason or another. The only negative I am aware of with this setting is running high numbers, remember it is not recognizing the sugnal til it is present for the specified amount of time you enter there. So the machine is still traveling all of the time between when a limit or home switch is triggered and the interval is reached. I am not trying to worry you here just start with say a value of 100, see if it works. If it does leave it alone. Btw each microsecond (the amount of time per  of this setting) is 0.000001 x 40 of a second. Probably not too much travel for a couple of hundred of those LOL.

not sure
That all right. If problems with noise turn out to be the culprit, we will get back to that.

there is a emi filter on the plug to the control box
Excellent at least incoming lines are quieted.

the box has a ground inside for the control box...
Is this just a chassis ground? (the green wire from a typical ac wiring in the US) Is there a wire from the power supplies (that feeds the drivers) V- terminal to this same ground point? Though this is the negative supply of the vdc, it also needs to be tied to the chassis ground, along with the incoming ground of the ac and the shields of your stepper wires and limit switches.
 
the kit is a cnc router parts nema  34 built by them
They most likely use off the shelf components like everyone else.

 can you pm me with info and i will send pics from my phone
As a last resort I will be glad to but you can post pictures directly thru tapatalk if you are using a phone. Dont be embarassed about wiring or organization.

thanks keith
I want to die in my sleep like my grandfather, not like the passengers in the car! :-)