Re: [Emc-users] Probe with PCB piece

[Gene Heskett]

On Tuesday 17 November 2020 04:22:01 andy pugh wrote:

> On Mon, 16 Nov 2020 at 20:59, Alan Condit  
wrote:
> > However, when I read the instructions on G38.2 it talks about the
> > switch opening. Can I invert the probe signal and use it for switch
> > closing?
>
> Where are you reading? The G38 docs don't talk about opening or
> closing, they talk about contact and loss of contact:
> http://linuxcnc.org/docs/2.8/html/gcode/g-code.html#gcode:g38
>
> The HAL pin probe-in should go high on contact. How that is achieved
> electrically and HALogically is implementation dependent.

Which is why I suggested using the in_not pin if its available. The 
spindle is generally grounded and using the bit of pcb for a contact 
results in a logic 0 on contact. Feed that into the in_not pin.
If using a std bob input the not module MUST be above anything in the 
addf order hat uses it else the approach velocity error gets out of 
hand, and you may damage the pcb with the first approach from the 
resultant servo-thread timed overshoot.  I also invert that when hole 
finding where I have a 3/4" teflon rod holding a length of 12 gauge 
copper wire with the probe wire separated into half the strands on 
either side of the probing wire and twisted back together. I run the 
spindle backwards at 500 or so revs, and probe all 4 quadrants then 
center it both ways and touch off. And I regularly can rerun the 
holefinder code with no more than .0002" of error either way the 2nd 
time. There, because the probe is spinning, I have a capacitor on the 
probe input that is discharged by a microsecond contact, and still has 
not recharged the capacitor by the time the servo-thread read rolls 
around at the next random millisecond.

But because my spindles aren't fixed, I use the pcb method for setting 
TLO's.


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] Probe with PCB piece

[andy pugh]

On Mon, 16 Nov 2020 at 20:59, Alan Condit  wrote:
>
> However, when I read the instructions on G38.2 it talks about the switch 
> opening. Can I invert the probe signal and use it for switch closing?

Where are you reading? The G38 docs don't talk about opening or
closing, they talk about contact and loss of contact:
http://linuxcnc.org/docs/2.8/html/gcode/g-code.html#gcode:g38

The HAL pin probe-in should go high on contact. How that is achieved
electrically and HALogically is implementation dependent.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] Probe with PCB piece

[Gene Heskett]

On Monday 16 November 2020 15:37:08 Alan Condit wrote:

> Hi,
>
> I want to set up to probe for workpiece height (tool length) with a
> piece of PCB  and a wire hooked to probe input and another piece of
> wire and an alligator clip wired to probe ground.  I would clip the
> alligator clamp to the tool and set the piece of PCB on top of the
> work surface. So, the circuit would close when the tool tip touched
> the PCB. However, when I read the instructions on G38.2 it talks about
> the switch opening. Can I invert the probe signal and use it for
> switch closing?
>
> Thanks,
> Alan
>
Yes, been doing exactly that for years Alan. If using a mesa interface, 
you may be able to "net" it to the in-not pin and skip the invertor as 
its one less thing to worry about in your addf order.
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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[Emc-users] Probe with PCB piece

[Alan Condit]

Hi,

I want to set up to probe for workpiece height (tool length) with a piece of 
PCB  and a wire hooked to probe input and another piece of wire and an 
alligator clip wired to probe ground.  I would clip the alligator clamp to the 
tool and set the piece of PCB on top of the work surface. So, the circuit would 
close when the tool tip touched the PCB. However, when I read the instructions 
on G38.2 it talks about the switch opening. Can I invert the probe signal and 
use it for switch closing? 

Thanks,
Alan

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