using Sheetcam and PlasmaC re Kerf

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13 Jun 2020 17:56 #171467 by Clive S
This might be a daft question to some BUT.

When using sheetcam to make the gcode for a part and you put a kerf of say about 2mm when the gcode gets past to PlasmaC

which kerf does it use ie dose it use the kerf from sheetcam or PlasmaC.

Because sheetcam will generate the gcode with its kerf so how does PlasmaC know about it?

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13 Jun 2020 21:17 - 13 Jun 2020 21:17 #171495 by rodw
Sheetcam compensates for kerf width internally rather than using G41 & G42

For Plasmac to compensate using G41/G42, You need to add this to yoour code
linuxcnc.org/docs/2.8/html/plasma/plasma...#cutter-compensation
But be aware of the caveat mentioned there.
This is becasue there is no gcode control of digital and analog pins while compensation is active.

I just leave it to Sheetcam...
Last edit: 13 Jun 2020 21:17 by rodw.
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13 Jun 2020 21:41 #171501 by Clive S
Rod thanks but that really dose not answer my question if sheetcam using the kerf then I use the tools set up in PlasmaC does it add to the kerf what PlasmaC uses !!

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13 Jun 2020 21:58 #171505 by rodw
Well, if you look at the generated code, it will tell you if plasmac is offsetting it. But yes, I guess if you tell it to cut to the right of left of the tool path sheetcam made, it will increase the offset. (unless you tell sheetcam not to apply the offset)
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13 Jun 2020 22:02 - 13 Jun 2020 22:09 #171508 by Clive S

Well, if you look at the generated code, it will tell you if plasmac is offsetting it. But yes, I guess if you tell it to cut to the right of left of the tool path sheetcam made, it will increase the offset. (unless you tell sheetcam not to apply the offset)


I am surprised this has not been mentioned before. If that is so it would be nice to mention that in the manual.

If I read you right you should use sheecam with no kerf and let PlasmaC do the kerf. I think you just use the sheetcam tools. I do not and use the tools from PlasmaC

edit but thinking about it. without fire ring up linuxcnc (bedtime here) how would PlasmaC know about which side the offset is?
Last edit: 13 Jun 2020 22:09 by Clive S.

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13 Jun 2020 22:09 #171509 by rodw
I don't think Plasmac was originally built wit post processors in mind so its not really a Plasmac issue. Its up to the post processor.
But if you let plasmac do it, you can't apply hole rules or the like because they rely on digital and analog IO pins. (My take anyway)
Thats a linuxcnc limitation.

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14 Jun 2020 00:03 #171518 by phillc54

I don't think Plasmac was originally built wit post processors in mind so its not really a Plasmac issue. Its up to the post processor.
But if you let plasmac do it, you can't apply hole rules or the like because they rely on digital and analog IO pins. (My take anyway)
Thats a linuxcnc limitation.

Thats the way I read it as well.
PlasmaC can only cut what the code tells it to. If your PP compensates for kerf width then you wouldn't tell PlasmaC (well really it is LinuxCNC) to apply cutter compensation. The limitation of cutter comp and digital/analog pins is mentioned in the docs.
So PlasmaC does not automatically apply kerf width (cutter) compensation.
It is applied by LinuxCNC if you specify it (G41.1 G42.1) You should notice in the standard PlasmaC startup that cutter compensation is turned off (G40).
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14 Jun 2020 07:05 #171568 by Clive S

I don't think Plasmac was originally built wit post processors in mind so its not really a Plasmac issue. Its up to the post processor.
But if you let plasmac do it, you can't apply hole rules or the like because they rely on digital and analog IO pins. (My take anyway)
Thats a linuxcnc limitation.

Thats the way I read it as well.
PlasmaC can only cut what the code tells it to. If your PP compensates for kerf width then you wouldn't tell PlasmaC (well really it is LinuxCNC) to apply cutter compensation. The limitation of cutter comp and digital/analog pins is mentioned in the docs.
So PlasmaC does not automatically apply kerf width (cutter) compensation.
It is applied by LinuxCNC if you specify it (G41.1 G42.1) You should notice in the standard PlasmaC startup that cutter compensation is turned off (G40).


So If I am understanding this correctly then you don't use the kerf in PlasmaC if you have used it in sheetcam when using the Post P

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14 Jun 2020 07:06 #171569 by phillc54

So If I am understanding this correctly then you don't use the kerf in PlasmaC if you have used it in sheetcam when using the Post P

Correct, otherwise you will end up undersize by the kerf width.
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14 Jun 2020 07:52 #171572 by Clive S

So If I am understanding this correctly then you don't use the kerf in PlasmaC if you have used it in sheetcam when using the Post P

Correct, otherwise you will end up undersize by the kerf width.


Thanks Phill. I am going to be cutting a proper job today and don't want to look more of a prat than I am:(

So if I want to use the tools I have setup in PlasmaC do I not use the kerf in sheetcam then sheetcam would generate the gcode
0n-the-line (ie no offset) but then will PlasmaC do the offset but then it would not know which side to do the offset on!!

sorry to be a PITA

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