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Discussion Starter · #1 ·
I hope this is the place for this 馃

I am new to using a 3018 engraver. I have been getting familiar with using the machine with UGS, have installed limit switches, and set it up for homing.

After a homing cycle, he machine coordinates become (in mm): X-199.0, Y-199.0 Z-1.0. I would like the coordinates to end up at all zeros.

I am assuming that the resulting coordinates are where it is after "pull-off", ie, after the axis pulls away from the limit switch after making contact, which is 1mm.

So how does either grbl or ugs define what the resulting machine coords are after homing, and how can I change these?

Thanks....
 

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It doesn't matter. You tell the machine (Grbl, via UGS) where the zeros are based on your job needs. To cut a job, generally, you jog the spindle in x and y to where you want the zero to be on your workpiece and set x and y to zero. Then you jog your tool (bit) tip to zero (either the workpiece top or the bed top, based on how you designed your job) and set z to zero. Then you can start your job.

If you wanted to, you could set x, y and z to 0 immediately after homing. But, unless your job workpiece is set up so it's zero is right there, it is kind of meaningless.
 

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Discussion Starter · #3 · (Edited)
It doesn't matter. You tell the machine (Grbl, via UGS) where the zeros are based on your job needs. To cut a job, generally, you jog the spindle in x and y to where you want the zero to be on your workpiece and set x and y to zero. Then you jog your tool (bit) tip to zero (either the workpiece top or the bed top, based on how you designed your job) and set z to zero. Then you can start your job.

If you wanted to, you could set x, y and z to 0 immediately after homing. But, unless your job workpiece is set up so it's zero is right there, it is kind of meaningless.
It matters to me. Yes, I get what you're saying and all. But you are talking about soft coords/zero, and I'm talking about the machine coords. The machine coords after homing will always be the same. The soft zeros are volitile, and mean nothing after a power outage, in which case you'd have to start all over and find zero again. I home the machine, set up my project and set my soft zero, then record the machine coords. Then if a power outage occurs I can easily get back to my zero based on the machine coords I recorded.

Wanting to have the machine coords be exactly 0,0,0 after homing is probably more of an autistic thing as it makes more sense to my brain. The machine coords at the zero point of my workpiece would then reflect the exact distances from the homing position.
 

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Discussion Starter · #4 ·
Wanting to have the machine coords be exactly 0,0,0 after homing is probably more of an autistic thing as it makes more sense to my brain. The machine coords at the zero point of my workpiece would then reflect the exact distances from the homing position.
If the machine coords after homing are 0,0,0, then after a power outage all I would have to do is home the machine and then send:

Z[some safe value above the work]
X[machineX I recorded after zeroing originally] Y[machineY I recorded after zeroing originally]
Z[machineZ I recorded after zeroing originally]
*

and not have to do any math (let鈥檚 see, do I subtract -199 or add?). I also wouldn't have to record both the initial machine coords after homing, then again after zeroing. It would just be easier for my brain.

*Then set zero at this location and I鈥檓 back where I was.
 

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Welcome to the forum, Kevin..
 

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Discussion Starter · #7 ·
I think I have this figured out now:

I have my X,Y limit switches at -X,-Y position ("lower" "left" corner). Z limit switch is in +Z position. These are accordingly configured using $23:

$23 = 3 (Homing direction invert mask)
(See "Axis config table": https://www.diymachining.com/downloads/GRBL_Settings_Pocket_Guide_Rev_B.pdf)

Now $130, $131 and $132 are X,Y,Z max travel, respectively. These are the values used for soft limits if enabled. In my case I had:

$130 = 200
$131 = 200
$132 = 200

In the case of my inverted homing directions, grbl is using $130 and $131 to calculate the machine position, ie:

machineX = 0 - $130 = -200(mm)
machineY = 0 - $131 = -200(mm)

This is the point where the limit switches close. After pull-off, which is 1mm,

machineX = -200mm + 1mm = -199mm
machineY = -200mm + 1mm = -199mm

as the spindle has traveled 1mm each in the positive direction.

So, I am able to accomplish what I want for X,Y using:

$130=1
$131=1

Of course this will only work if I don't use soft limits (which I am not.)

The resulting Z will still always be -1mm (0 - 1mm travel after pull-off), as Z homing is not inverted. (As Z homing is not inverted, $132 has no bearing.) I apparently have no control over this* This is not a big deal to me; I can just remember to add 1 to the Z value when I resume my zero after a power outage (see 2 posts above.)

So now my settings are:

$20=0 (Soft limits disabled)
$130=1 (X - Max Travel)
$130=1 (Y - Max Travel)
$132=30 (Z - Max Travel) (inconsequential here actually)

The resulting machine position after homing is now 0,0,-1

Yay!

*Actually, I came across something which talked about telling the firmware to use the after pull-off position rather than the limit switch break position to set machine zero. However, 1) I have not been able to find it again :-( , 2) It may have been for some firmware other than grbl, because I see nothing in $$ which would indicate a setting for that.
 
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