Setting value of home switch location?

04 Feb 2020 02:53 - 04 Feb 2020 12:22 #156485 by mooser
Finally got the limit switches back on (still waiting on changing the X but for now it's fine) and came across something that I can't seem to figure out (add another to the list)
I'm using a combined limit/home switch on the Z at the tailstock end
I've got one switch on the X that is triggered on both ends of the travel before the ballscrew bottoms out either way

Home is set and both seem to work, it travels up, trips the switch and then backs off .25" for the home
I've set both axis to move in from there 0.5 for the starting position (off the switches)

First question
On the X, it sets the home to 0.0000 and moves in to .5 (diameter) with the cross-slide out towards the user (largest diameter) I can't seem to change this value so that when it hits the switch it set it to say 10" rather than zero. I tried adding values for the offset but that is moving the tool to that position after zero rather than setting zero

Looked at the documents for the homing in the ini file and tried a handful of changes but none were giving my what I expected.

Second Question
On the Z axis, when it touches off and moves ahead it's going to -1.9456 instead of -.25 when it rapids off the switch after setting zero. Visually looks like it's moving the .25 inches but it's setting the Z DRO value to this other number (1.9..) which is sort of what I was looking to do (see first question above) but I don't have any seemingly random 1.9xx number in the ini file anywhere and the Z looks like the X as far as I can see

Last edit: 04 Feb 2020 12:22 by mooser.

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04 Feb 2020 15:05 #156507 by andypugh
1) This is normal for homing. You need to, additionally, "touch off" a tool to the diameter to set up your work offsets.
Also make sure that you are viewing relative/work coordinates rather than machine coordinates.

2) You might already have a work or tool offset active.

What I do (but there are other ways) is to touch-off the work coordinates (G54 and friends) using a particular tool (tool 1 in my case, turn and face tool). Then I make a test cut, measure, and touch-off again to the measurement.

Then other tools are touched-off by their own test-cut, except that the other tools are touched-off in to the tool offsets, so that the tool table holds their offset from the reference (Tool1) tool.

Typically the X axis remains the same, but the Z is often touched-off to different positions. This can be done with any tool, in to the G54 coordinate system as long as the tool offset has been loaded (G43 after M6)

It is possible to configure LinuxCNC for lathe-like tool-changes, using only Tnn but that is probably a subject for later.

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04 Feb 2020 15:11 #156508 by Todd Zuercher
You would need to set both your home and home offset to something like this.
HOME = 10
This will set the point where your home switch triggers to 10.5 and then move a half inch away from that point and stop.

But configuring it this way might not be wise. If a a CAM program calls a G53 X0 to move to a safe position for a tool change for example. The tool might crash. It might be better to leave the home position as zero and use a machine offset (G54) to set the home position as 10.

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04 Feb 2020 20:33 #156537 by mooser
Sounds like a good plan, I was just looking for a way of setting the home switch location other than zero (on the router I use the home switches are both set to -3 so the corner of the "table" is 0/0)

Andy, I set my tools the same on the old mach3 as well.
Also there was a value in the G54 z-axis from somewhere when I was playing around I guess. All good now

Todd, agreed, I'll leave it alone.

Thanks guys, onto the last bit I think and deal with the gears

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