Z homing touch plate - hardware/software input

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09 Sep 2019 21:15 #144631 by randypetersen
Here is some pics of the Z touch plate that came with my CNC. However, I cannot figure out for the life of me how it would work.




As you can see there are 2 wires going to the plate, both are connected to plate so there is no resistance between those 2 wires. They run to the controller and have been identified.

My understanding is that I would need a wire going to the tool and one to the plate. However I can't find any conductor going from the tool/spindle to the controller. I think the spindle is insulated? Would I have to run another wire to the spindle that would be clamped on tool? or is there any other way around this?

I created one of these pretty simply with my old parallel port / mach3 setup. I did have to clamp on to the tool though. Wasn't sure if that would always be required of if there was a better way?

Then what's the best practice for setting up a Z homing procedure within LinuxCNC?

Thanks for any info!
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10 Sep 2019 06:06 #144661 by pl7i92
seams like a omic sence

get 5V on the plate and mesure the resistence if a steel tool touch the plate

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10 Sep 2019 06:55 #144672 by tommylight
If using parallel port, just ground the spindle/machine and wire the sensor to on of the inputs on the parallel port.
No wires needed. Parallel port can sense input pins going to ground so that is easy.
If you have a BOB, you might need to add a pull up resistor for it to work.

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10 Sep 2019 07:01 #144674 by pl7i92
@ tommy
dont you think it workes like renishow high sense reed relai
the large detector plate lets me think of this

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10 Sep 2019 07:06 #144676 by tommylight
It's a metal plate so the reed relay will not work inside it. Reed relays react to magnets or magnetic field.

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10 Sep 2019 07:17 #144678 by pl7i92
not direct reed relais some kind of that sence

BUT im with you it may only ((black pice)) be a pice of Electric shield to the Mashine
he needs to get a meter on to see what hapens without a mashine connect

meter BLACK to one pin of detector connector
the other to a BIT/tool in Hand and just touch
while meter is in Detect Thrue mode / ""Durchgangsprüfung""

then he is fine and can simply direct BOB connect via ground detect
I DO NOT RECOMED BOB ground on Mashine AS so many using that

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09 Oct 2019 16:23 #147575 by randypetersen
I still haven't had any luck on this, maybe I need to purchase or build a different Z plate.

Between the bit and the ground there is some resistance but it's a connection. I missed it at first because I was just listening for a continuity beep from my meter, however there is a connection between bit and ground wires.

How could I wired that up?

I am using a Mesa 7i77 & 7i92 boards.

Anyone have any thoughts?

Thanks!
Randy

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11 Oct 2019 13:55 #147702 by randypetersen
Anyone have any experience with these tool height gauges, I would think that would be helpful once I get my automatic tool changer working.


It would still be nice to get the Z touch plate so I could have a material thickness correct?

Thanks,
randy
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18 Oct 2019 13:08 #148196 by andypugh
You might be able to add an opto-isolator (or even a relay) to the touch-plate circuit to convert the resistance change to an on/off signal for the GPIO.

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