Newbie question about offsets and homing

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14 May 2012 13:58 #20081 by Bullseye
Thanks. I will try the modified code today and let you know how it worked for me. Can you explain how homing works when you do not have a dedicated home switch? Also, it seems that the homing process is more an assigning the current point to X0 Y0 Z0 than actually moving the tool to the desired point. I know that you typically want to accomplish both actions when you perform a home operation but no movement occurs unless you issue a G0 or G1 command right? I keep struggling with how (the correct way) to get the tool back to the home position accurately without having to manually touch off on each axis when I want to return to the home position. I know that these are pretty basic questions, but as good as the documentation is, I just cannot grasp this operation.

Bill

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14 May 2012 14:45 #20084 by BigJohnT
cncbasher wrote:

John :
M2 is End program (usualy with reset , no rewind )
M30 is End program ( always with reset and rewind )

so a slight variation John

sorry for hijacking the thread , but just to answer Johns query etc ..
good work on the gcode tutorial to


IIRC LinuxCNC does not have a reset or rewind and the docs suggest that M30 is to exchange pallets. I don't think M30 really does anything that I can see anywhere so better to use M2 with LinuxCNC.

Thanks, if you notice anything missing/wrong or needed on the tutorial let me know.

John

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14 May 2012 14:51 #20085 by BigJohnT
Bullseye wrote:

Thanks. I will try the modified code today and let you know how it worked for me. Can you explain how homing works when you do not have a dedicated home switch? Also, it seems that the homing process is more an assigning the current point to X0 Y0 Z0 than actually moving the tool to the desired point. I know that you typically want to accomplish both actions when you perform a home operation but no movement occurs unless you issue a G0 or G1 command right? I keep struggling with how (the correct way) to get the tool back to the home position accurately without having to manually touch off on each axis when I want to return to the home position. I know that these are pretty basic questions, but as good as the documentation is, I just cannot grasp this operation.

Bill


As you have found out without a home switch the current position is the machine home position when you press Home. One workaround for not having homing switches is to establish some match marks for each axis. After starting up LinuxCNC jog each axis to the match marks and press Home. Once the machine is homed G53 G0 X0 Y0 Z0 will return the machine to the home position no matter what offsets are in effect. Once homed you then proceed to touch off each axis to the material/work holding device as needed. My tutorial covers this aspect.

John

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14 May 2012 16:04 #20086 by Bullseye
Thanks for confirming that what I experienced is normal operation. It looks like I will have to take the photo interrupters and set up some home switches. I have read your tutorial and it is a lot clearer than some of the LCNC documentation.

Bill

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14 May 2012 16:17 - 14 May 2012 16:18 #20087 by andypugh
Bullseye wrote:

Thanks for confirming that what I experienced is normal operation. It looks like I will have to take the photo interrupters and set up some home switches.


I am confused now. I thought you said that you had combined limit/home switches?

What happens when you press the "home" button?
Last edit: 14 May 2012 16:18 by andypugh.

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15 May 2012 00:15 #20090 by BigJohnT
Bullseye wrote:

Thanks for confirming that what I experienced is normal operation. It looks like I will have to take the photo interrupters and set up some home switches. I have read your tutorial and it is a lot clearer than some of the LCNC documentation.

Bill


Even though I re-wrote a large chuck of the LinuxCNC documents to translate them from programmer speak they are still a reference manual to the various parts of LinuxCNC. This it why I cobbled together the tutorial to bridge the gap between a new user and the reference manuals. My hope is once you get past my tutorials you can find what you need in the manuals.

John

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15 May 2012 08:51 #20092 by Rick G
Have you looked at "POSITION_FILE = "

You might want to take a look here...

old.linuxcnc.org/component/option,com_ku...imitstart,0/lang,fr/

Rick G

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