Automated homing of X and Y axis

On machines without limit switches many just set a home position at say X0Y0Z0 and have a mark, line or hard stop at that position. When starting the machine confirm that it is in the right position, set home and then depend on the soft limits to keep from going beyond the physical limits. When done work issue a G53G0X0Y0Z0 and the machine will return to the home position. Linuxcnc can retain the offsets so you can return to your previous work positions.

Yep, hitting a clamp can ruin your whole day, hitting a drywall screw with a router bit is not much better.

Rick G

Here's a couple videos I took today. As I mentioned earlier, this machine worked well using Mach3, so I'm just trying to get this tuned using LinuxCNC.
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This first video is where I'm trying to home the Z axis. The endmill stops at the copper plate, but I have to repeat a couple times to get it to home. LinuxCNC give me a "Home switch inactive before start of backoff move" error in the bottom right corner of the screen.
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The second video shows the machine locking up on the X-axis when trying to jog using the shift key. Is there a way to tune this out since it loses steps when this happens.
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due to the additional weight of the z axis and working against gravity , lower the acceleration , and if your using microstepping reduce this to say 1/2 steps
your trying to move as a faster rate then the z axis can handle , hence missing steps , so slow everything down by 50% and then try again , keep repeating untill you get no missed steps , and then increase in smaller steps till your happy .

you can't home using the procedure your trying , this is essentially the wrong area , but you can touch off tools , this is not the same thing
home is for initiation of the work area setting 0,0 of x y z ( z in your case is top of the z travel ) to a home switch once you first switch the machine on
not for setting work zero.

tool touch off is setting the correct tool length where the top of the material for example would be zero in your work envelope , rather than the machine

also make sure the top of your pcb is clean if using for a touch off , your felt pen could cause the pcb to have an insulated surface .

Just to make sure I'm up to speed here . .
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Since I have determined that limit switches are impractical on my little machine, the term "homing" is "N/A". In my case the G53 coordinate system can be ignored. I don't need to get the little "axis homed" symbols on the LinuxCNC screen.
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When I cut, I'm using the G54 coordinate system and setting my "work zero" to (0,0,0) and then manually making sure I'm not going to cut anything bad.
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When I get into the shop next, I'll give the g-code file a shot at setting the X and Y axis . .
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Thanks for the help!!

cncbasher wrote:

due to the additional weight of the z axis and working against gravity , lower the acceleration , and if your using microstepping reduce this to say 1/2 steps
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I am having trouble with the X-axis (posted video). . . is that what you meant?
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Do I need to lower the acceleration?
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yes lower the acceleration and or reduce your step timing etc , if you listen to the stepper , you can hear it screech as it try's to go full speed
and it cant keep up ..
you dont say what stepper drivers your using , so let us know , but essentially slow things down by 50% till it works and then retune to suit
if your using microstepping greater than 4 , then again , try lowering

Since I have determined that limit switches are impractical on my little machine, the term "homing" is "N/A". In my case the G53 coordinate system can be ignored. I don't need to get the little "axis homed" symbols on the LinuxCNC screen.
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When I cut, I'm using the G54 coordinate system and setting my "work zero" to (0,0,0) and then manually making sure I'm not going to cut anything bad.

No you still need to home the machine. You do not need home or limit switches. Look at the previous posts. When homed and soft limits set linuxcnc will keep you from moving outside the machines limits.
First home the machine then touch off on your material.
An easy way to do this is to have hard stops, say z all the way up x to the left and y closest to you.
www.linuxcnc.org/docs/html/config/stepco...ting_without_limit_a

Rick G

OK, I'm making progress here. . . Please be patient folks, I'm just a hobbyist and have no formal training in this. I just found John Thornton's G-code tutorials, any others you guys can point me to would be helpful.
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I was able to fix the X-axis by reducing the acceleration and max speed of the axis. Done.
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Also tried homing the machine and was able to set the G53 system. I never messed around with the soft stops before, but was able to try them out. Neat feature. When I set the machine home, I assume I should set it just a bit off the hard stop, correct?
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I need to learn more about how the coordinate systems work since when I tried to touch off on a piece of wood to set the G54 Z0 I ended up changing the Z home. Operator training needed. . .
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Previously when I would try to home the Z axis, it would begin slowly moving down until it made contact with my copper plate. Now that I am homing my machine, I am setting the top of the travel at G53 Z3.0. To get the Z axis to stop hunting for the plate, I changed the input pin in "stepconfig" from "Z-axis home" to "Probe Input".
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My question now is how am I going to find the top of my stock using the "probe input"? Is there a specific G-code command to use? Can I set it up to a button on LinuxCNC?
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Thanks again for everyone's patience.
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When I set the machine home, I assume I should set it just a bit off the hard stop, correct?

I set it right on the hard stop for repeatability.

I need to learn more about how the coordinate systems work since when I tried to touch off on a piece of wood to set the G54 Z0 I ended up changing the Z home. Operator training needed. . .

Home the axis then use touch off to set the top of the material. On a router I set the Z axis with the spindle at the top of it's travel.

You can use a probe command to find the top of the material.

linuxcnc.org/docs/html/gcode/gcode.html#sec:G38-probe
and
wiki.linuxcnc.org/cgi-bin/wiki.pl?Plasma...erial_top_with_Probe

Rick G