Safe Z is backwards with homing enabled

gSender ❓ Question
1

With homing enabled and a positive safe Z set, when go to X is hit the machine moves down instead of up by the safe Z amount.

According to this thread that is the intended behavior.

I can’t remember but was the direction of travel from home changed sometime without changing the safe
Z behavior? As gsender works now the Z0 is at the top of the machine and Z goes into the negative as it descends thus subtracting the safe height when homing is enabled is backwards, I believe.

2

First thought is that your Z motor wiring is backwards. That also would explain the safe z behavior.

Is this a recent build or repair?

3

No it’s not a recent build and the console output shows the command to move Z down. It’s my step dads machine that was doing this, I don’t use the safe Z “feature” in gsender personally. But this behavior explains his propensity for breaking bits.

Does your machine not have Z0 at the top and move into negative numbers as it goes down?

Thanks,
_Michael

4

Just confirmed the behavior on my longmill which works great. The following console output is from homing the machine and hitting go to XY0 with safe height of 10mm and homing enabled.

gSender - [Grbl]
Connected to COM6 with a baud rate of 115200
client $H
ok
feeder G53 G0 Z-10
feeder G90
feeder G0 X0 Y0
ok
ok
ok

I think the Z move in “G53 G0 Z-10” should be positive not negative.

edit: Using gSender 1.0.5

5

Been reading a bit because I am no gcode expert. I now understand that G53 means use absolute machine coordinates. So if the machine is below the negative of the set safe height it will move up and if the machine is above it will move down.

It still seems counter intuitive to me that a larger safe height in gSender is closer to the spoil board than a lesser one.

Hope this all makes sense. I will try to clarify if it does not. I just want to make gSender better if possible as I like it better than the alternatives I have tried.

Thank you all,
_Michael

6

Hi @_Michael , I recently added some new documentation to the gSender docs to explain this issue. Essentially:

If you have ‘homing’ enabled a value of 5mm will make the CNC move to 5mm offset from the max Z-axis travel, make the goto movement, and then return back to where the bit started, whereas if homing is disabled it will move 5mm upwards from the current position and then move 5mm back down at the end. This flip in behaviour is because ideal safe height movements should be as high up as possible to avoid bit collision which is only possible with a homed machine, otherwise safe height movements need to be kept to a minimum to avoid situations where gotos are used on taller material and the Z-axis moves past its maximum point.

I hope that clears up for you the reason for this decision. If you have any other questions lmk

7

Thanks for taking the time to explain how that works and updating the docs.

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