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Configuring Z height
After homing ( with G28 ), the machine knows it is at Z maximum position if your machine homes to max, and at Z minimum position if your machine homes to min.
Because of this, it will read the configuration option gamma_max or gamma_min depending and set the current Z position to that value.
So after homing, the Z position is set to gamma_max or gamma_min.
This means for example if you home to max that if your hotend is 300mm above your bed after homing, and you set gamma_max to 300, after homing, you can just tell the machine to go to Z position 0, and it will go to the bed’s height.
To put it simply, setting gamma_max or gamma_min is your way of telling Smoothie what the distance is between your bed, and the hotend, when the machine has just homed.
To find the right value for gamma_max or gamma_min do one of the following:
Simplified manual adjustment method (Recommended method)
First home the machine:
G28
Then move to the point the machine currently thinks is Z 0:
G0 Z0
Then move the head to the bed by jogging, using Pronterface’s arrows, the panel, the web interface or whatever other method is adequate in your case.
Finally issue the M306 Z0 command which will use the current Z position as a homing offset:
[!NOTE] You cannot use M306 unless you have Z homing endstops, if you can’t home Z then you can’t set homing offsets.
M306 Z0
Then save to the SD card with M500:
M500
Next time you home, the machine will know how high above the bed it is.
Finding gamma_max manually
First home the machine:
G28
Then set the current Z position to 0:
G92 Z0
Then move the head to the bed by jogging, using Pronterface’s arrows, the panel, the web interface or whatever other method is adequate in your case.
Once the head is exactly at the bed, issue this command:
M114
This will return the position of all axes. The current position of the Z axis is the value you must use as your gamma_max value.
Now simply edit the configuration file to set this value, and reset the board.
Alternatively (delta only) you can use the M665 Z(distance) command to set the value in the config override system, and M500 to save that value to the SD card.
The gamma_max value in the configuration file is ignored if M665 is set and saved.
Next time you home, the machine will know how high above the bed it is.
Finding gamma_max with a probe
If you have some sort of probe attached to your head ( or below your head ), which triggers when the hotend gets close to the bed, then you can use this to find your gamma_max value without manually jogging.
Now there are two different cases here:
- Either when the probe is triggered, the hotend is exactly at bed level ( this is the case of probes under the bed, or probes that trigger when the hotend itself is pushed )
- Or, when the probe is triggered, the hotend is above the bed by a given distance, which we will call the z probe offset ( this is the case of servo-retracted probes, bltouch, inductive probes, IR probes, etc ).
First home the machine:
G28
Then ask the probe to go find the bed:
G30
This will report the distance traveled by the probe.
Your gamma_max value is that reported distance, plus the z probe offset ( distance between the probe triggering point, and the bed ).
For example, if you home, then do G30, and it reports a height of 311mm, and your probe is 7mm below your hotend, then your gamma_max is 311 + 7 = 318mm.
Simply edit the configuration file to set this value, and reset the board.
Alternatively you can use the M665 Z(distance) command to set the value in the config override system, and M500 to save that value to the SD card.
The gamma_max value in the configuration file is ignored if M665 is set and saved.
Next time you home, the machine will know how high above the bed it is.
Automatically finding the bed with a probe
Smoothie allows you to save both the Z height, and the delta calibration data, to the SD card.
This means you do not need to probe every time you start the machine, you only need to do it once, and save the values, which will then stay valid as long as your machine’s geometry doesn’t change.
This means you can have a removable probe that you only connect and attach to the head at the rare occasions when you need it.
However, if for whatever reason you have a fixed ( or retractable ) probe on your head ( or sensors below your bed ), then you might want to automatically probe at the beginning of each print.
To do so, simply change your slicing program’s “beginning of file” G-code sequence, and replace:
G28
with:
G28
G30 Znnn
When nnn is the distance between your probe’s triggering point, and the bed ( or probe offset ):
The G30 Znnn command moves the head until the probe triggers, then sets the current Z height to nnn.
So for example if your probe triggers when the hotend is 5mm above the bed, do G30 Z5, and if your probe triggers exactly when the hotend touches the bed, do G30 Z0.
[!NOTE] Behind the scenes G30 Z0 does a G92 Z0, so you can save this if you set ‘save_g92 true’ in config and issue M500 that saves the offset at 0. Note that G92 is creating a new coordinate system called the Workspace coordinate system (or WCS) it is worth reading up on how that works.
If you are doing this manually you can save time by jogging the Z to within 5mm of the bed then issue the G30 Z0.