Problem storing Z touch-off value

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16 Nov 2019 16:39 #150476 by JohnnyCNC
Lately I have been having a problem with the Z value not being stored in linuxcnc.var after touching off using my touch plate. I have been using this setup for about a year with no problems. My touch plate has a button on it that when pushed runs the routine shown below. It is not failing all of the time and I am 100% sure that It wasn't me forgetting do the touch-off. I did a touch-off, ran a peck drilling op which plunged the bit right through the part. I touched off again and the operation worked correctly. I am running 2.7.14. Any ideas on what might cause this to happen?

<pre>
o100 sub
G20
( Set current Z position to 0 so that we will always be moving down )
G10 L20 P0 Z0
( Probe to Z-.5 at F2 [Uses machine units, I work in inch, this is meant to be slow!] )
G38.2 Z-.25 f2
( Set Z0 at point where probe triggers with offset of +1.0095 [this is the thickness of my touch plate. You must adjust this for your plate / setup] )
(G10 L20 = Set Coordinate System // P - coordinate system 0-9 0 = Not active)
G10 L20 P1 Z1.0095
( Rapid up to Z.5 above the material )
(G10 L20 P1)
(Use machine coordinates)
G90
G53 G0
(Incremental mode)
G91
(Rapid Z up 1 inches)
G0 Z1
o100 endsub
</pre>

Thanks
John

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16 Nov 2019 16:49 #150478 by pl7i92
if it is not failiong all the time it ISENT the SUB
there is a other problem

changing coordinate systems so many time isent a good behavior at alll
but it is up to you to do so

better
Move to a G30 location well above the touch plate
from ther it is always the same way to the plate
then just set the value you like
and go on with work

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17 Nov 2019 19:47 #150538 by newbynobi
You set the zero on G54, (P1)
If you gcode does not work in G54, it will crash!

Norbert

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17 Nov 2019 23:24 #150550 by JohnnyCNC
All of this has been working for a year now. The touch-plate I have is mobile. I place it on top of the work piece. Get the bit close and the press a button on the touch-plate and that runs the touch-off routine. I took the touch-plate apart and saw that there was a chance that I was getting a short inside the unit. I rectified that and I am now watching it closely to see if I still get failures.

John

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22 Nov 2019 13:03 #150909 by andypugh
The .var file is only used to store values between LinuxCNC boots. (I think)
Generally the values are kept in application memory.

Is it possible that the disk is nearly full and sometimes the .var file is failing to save?

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23 Nov 2019 01:19 #150995 by JohnnyCNC
So far I think it must have been a short inside the touch-plate. I saw two wires that were being squeezed together and the insulation appeared very thin so I rearranged that it so far no problem. I didn't think through the wiring and see if that even makes sense but so far so good. I'm pretty sure I have plenty of disk space but I will certainly will check. Although having said that I wouldn't be able to FTP .ngc file over to the machine if I was out.
The following user(s) said Thank You: Todd Zuercher

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04 Dec 2019 02:20 #151935 by JohnnyCNC
I think I found the culprit. I checked my tool table and found an offset on tool #3. Normally all tools have no offsets because I manually load the tool in the R8 collet and then set my touch-plate on top of the stock and do a "touch off". I may have hit the "tool touch-off" button at some point by accident. I think I would like to disable that button since I never use it.

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04 Dec 2019 11:13 #151972 by andypugh
If you have an R8 you could consider replicating the Tormach TTS system, then you could have repeatable tool length and use the tool table.

Search Ebay for "C3/4" holders. You want ones with the bigger shoulder, such as:
www.ebay.co.uk/itm/153748036661
The idea of TTS is that there is a _shortened_ 3/4" collet that both centres the collet chuck and pulls the shoulder back against the spindle nose. (That last point is an important part of the principle, and is what gives rigidity and length repeatability.

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