X,Y,Z position not zeroing after homing

Discussion about the arduino based g-code interpreter, grbl
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COMarcus
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X,Y,Z position not zeroing after homing

Post by COMarcus » Thu Aug 04, 2016 3:07 pm

I just installed homing switches, following the setup here:

http://docs.carbide3d.com/article/67-sh ... stallation

The switches work fine, the z-axis moves up, hits the switch, moves back down a bit. the gantry moves back to the top right corner, stops when it hits the switches. It doesnt set the coordinates to 0 though and when I try to manually do it in the software, it doesnt work either. When I give it a manual job command, it seems to move back to the place it was at before it was homed, then does the move. What am I missing here?

CastIrony
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Re: X,Y,Z position not zeroing after homing

Post by CastIrony » Thu Aug 04, 2016 3:35 pm

The homing mode in Grbl sets the absolute machine coordinate system (G53), while zeroing in Carbide Motion sets the first work coordinate system (G54).

This isn't a bug, it just lets you set your work origin point to anywhere on your machine and not just your absolute homing origin. Since work coordinate systems are all defined as relative offsets from the absolute coordinate system, your homing cycle will affect all of them.

If you want to use an alternate coordinate system (G55-G59), you can send the commands manually.
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twforeman
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Re: X,Y,Z position not zeroing after homing

Post by twforeman » Thu Aug 04, 2016 3:39 pm

See http://www.shapeoko.com/wiki/index.php/ ... te_Systems for more information on using the Work Coordinate Systems.
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COMarcus
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Re: X,Y,Z position not zeroing after homing

Post by COMarcus » Thu Aug 04, 2016 3:53 pm

Thanks for the replies. So if I home the machine, it moves up to the top right, load a gcode file...will it treat the home position as the 0,0,0 and move from there or will it move back to the WCS 0,0,0 and start from there?

Interesting that when I home it and then click the button to zero all, it does nothing. Should it set the WCS to the absolute at that point?

Bonch
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Re: X,Y,Z position not zeroing after homing

Post by Bonch » Thu Aug 04, 2016 6:33 pm

Homing set the boundry to where you tell the machine the homing position is. Normally it is the back right up position. You then would move the machine to you beginning cut position and zero your machine to your work piece. Normally the corner top of your work piece (or sometime center top). Then that is your 0,0,0 position for the project you will be cuting. Your gcode references off that position to do the cut and the home position is more like an exact reference point so the machine always knows where HOME is. Kinda like starting a trip from HOME. You know where that is on the map and everything is reference from there.

Hope that makes some sense.

Home - machine reference position

Machine Zero - work piece reference position

COMarcus
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Re: X,Y,Z position not zeroing after homing

Post by COMarcus » Thu Aug 04, 2016 7:39 pm

Bonch wrote:Homing set the boundry to where you tell the machine the homing position is. Normally it is the back right up position. You then would move the machine to you beginning cut position and zero your machine to your work piece. Normally the corner top of your work piece (or sometime center top). Then that is your 0,0,0 position for the project you will be cuting. Your gcode references off that position to do the cut and the home position is more like an exact reference point so the machine always knows where HOME is. Kinda like starting a trip from HOME. You know where that is on the map and everything is reference from there.

Hope that makes some sense.

Home - machine reference position

Machine Zero - work piece reference position
Yup, makes sense. I just want to make my machine zero equal my home position. Seems like a natural no fuss way to have it easily repeatable and simple. Then in my CAD software, I would just set my (0,0) X,Y spot to be the top right corner in whatever I am cutting. But it appears that is not doable?

Bonch
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Re: X,Y,Z position not zeroing after homing

Post by Bonch » Thu Aug 04, 2016 8:39 pm

You can change the home position to the front left corner instead of the back right corner. Most people index their work position in the front of the machine. I never fully understood why the back right is designated as home but you can change it. I am thinking it is the $23 code but dont remember for sure. You should probably look it up to make sure before you try it.

chamnit
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Re: X,Y,Z position not zeroing after homing

Post by chamnit » Thu Aug 04, 2016 9:49 pm

Regarding homing and where the origin is placed, please read this FAQ answer I posted recently about this topic. It should clear everything up.

https://github.com/grbl/grbl/wiki/Frequ ... im-used-to

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