Help with Limits and Switch Configuration and Homing

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13 Feb 2022 15:25 - 13 Feb 2022 16:00 #234702 by kbec
Hi guys, after a while I am back too trying to get machine running like I want it to. Now I am trying to set up my limits and homing it. I  only have one switch per axis. Here is how I have my switches wired, X, Y and Z. My Mesa card is also working right, as the LEDs for the inputs are lit unless the switch is tripped. I can jog the axes manually, so that piece is working as well.
So this is where I get really confused, Should I set the input as just a limit, or limit + home, I had them set to home before, but I don't think that is right. I am also unsure as to if the limits are minimum or maximum, since I only have the one on each axis.
These kind of make sense to me, but I think the search direction depends on what my limit in the other panel is. If I understand correctly, home will have the table centered on X and Y, I am not really sure where Z home should be. So for my X, I think I have 220mm travel, but I am not sure about the Home position or switch locations. Thanks for all your help, I am pretty close I think. I am just having a hard time with the coordinate systems.
Last edit: 13 Feb 2022 16:00 by kbec. Reason: Pics not showing correctly

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13 Feb 2022 15:41 - 13 Feb 2022 15:47 #234704 by Aciera
Much better to upload the pics to the forum then to expect people to copy paste the links. Also please make sure your pics are of a decent size so the content is actually readable for others who are trying to help you.
Last edit: 13 Feb 2022 15:47 by Aciera.

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13 Feb 2022 16:01 #234706 by kbec
Thanks, it did not work as expected, and you replied faster than I was able to fix it.

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13 Feb 2022 16:23 - 13 Feb 2022 16:26 #234709 by Aciera
Unfortunately it's still too small to read anything but generally your axis limits depend on the length of travel and on where the home/limit switch is located.
So if your Z axis has 100mm of travel and the switch is at the top then your z-maxlimit will be 0 and the z-minlimit will be -100. If your X-axis has, say, 200mm of travel and your switch is in the middle then x-maxlimit will be 100 and x-minlimit will be -100. If the spindle moves to the right (relative to the table) to find the home switch then it will be at the positive end and x-maxlimit will be 0 and x-minlimit will be -200.
So the max- and minlimits tell the controller how far the axis can be moved after the machine is in the home position.

[edit]
Note that all directions are relative to the spindle regardless if it is actually the table that moves.
Last edit: 13 Feb 2022 16:26 by Aciera.

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13 Feb 2022 19:15 #234724 by kbec
If I jog the Axix manually for X, using the - button in LinuxCNC, moving the table to the left, It will eventually trigger the switch.
For Y, the table comes forward and Z, the spindle goes up, the + button will bring the switch into contact

I think I need to label the inputs as a limit, but I am unsure as to if it is a max or min limit. I only have the one switch per axis, and it will end up being a hard limit I think, the other is derived with the travel.

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13 Feb 2022 20:02 #234735 by Aciera

X, using the - button in LinuxCNC, moving the table to the left

I think you might actually have your axis setup the wrong way. You should set it up according to the right hand rule. If you stand before your machine +Z should move the spindle up (as it does), +Y should move the spindle away or the table towards you (as it also does) and +X should move  the spindle to the right or the table to the left. Since your machine moves the table to the left when you are pressing - then you would need to change the sign for the 'STEP_SCALE' in the [JOINT_0] section in the ini file.
The switches can be setup as combined home/limit switches.  If the switch is activated when moving the table to the left then your spindle is moving to the right and thus to the positive end of the x-axis and so that would be the positive limit of your x-axis. Limit switches are 'hard' limits. Your machine will only have hard limits on the one side of the axis. The soft limits are then calculated by the controller with respect to the home position.

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13 Feb 2022 20:41 #234745 by kbec
I used pncconf and it made the change to the ini file, so now it operates as I think you said it should,
So for example, my X has 220mm travel
I want my home to be in the center, so I would set Positive and Negative travel distance each to 110
Then I have the part where I get confused. I am thinking I want the Final Home Position (Offset from machine origin) to be the table centered, so this would be 0
Then I think Home Switch Location (offset from machine 0 origin) would be 110
Then The home search direction, would that be Towards Positive limit?

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13 Feb 2022 20:59 #234748 by Aciera
Yes if you want the Home Position to be in the center the you would set the Offset value to half the axis travel.
The home search direction is positive if the home switch is on the positive end of travel.
Note that you will need to set min_limit to -110 (negative) not just 110

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13 Feb 2022 21:17 #234752 by kbec
Thanks a bunch for your help. I think pncconf set the limits correctly in the ini file. I still have to tweak some things, but I at least have it going to the switch, then backing off into what I have set.

I am kind of new to all this, generally what is the origin/home position set at?

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13 Feb 2022 21:28 #234756 by Aciera
On my machines it's spindle up, table forward, table right. But really after homing one usually uses work offsets (G54, G55 , ...)
The following user(s) said Thank You: kbec

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