klipper-dgus/docs/Manual_Level.md

This document describes tools for calibrating a Z endstop and for
performing adjustments to bed leveling screws.

# Calibrating a Z endstop

An accurate Z endstop position is critical to obtaining high quality
prints.

Note, though, the accuracy of the Z endstop switch itself can be a
limiting factor. If one is using Trinamic stepper motor drivers then
consider enabling [endstop phase](Endstop_Phase.md) detection to
improve the accuracy of the switch.

To perform a Z endstop calibration, home the printer, move the head to
a position near the center of the bed, navigate to the OctoPrint
terminal tab, and run:
```
Z_ENDSTOP_CALIBRATE
```
Then perform the ["paper test"](Bed_Level.md#the-paper-test) steps to
determine the actual height at the given position. One can then
`ACCEPT` the position and save the results to the config file with:
```
SAVE_CONFIG
```

It's preferable to use a Z endstop switch on the opposite end of the Z
axis from the bed. (Homing away from the bed is more robust as then it
is generally always safely to home the Z.) However, if one must home
towards the bed it is recommended to adjust the endstop so that it
triggers a small distance (eg, .5mm) above the bed. Almost all endstop
switches can safely be depressed a small distance beyond their trigger
point. When this is done, one should find that the
`Z_ENDSTOP_CALIBRATE` command reports a small positive value (eg,
.5mm) for the Z position_endstop. Triggering the endstop while it is
still some distance from the bed reduces the risk of inadvertent bed
crashes.

Some printers have the ability to manually adjust the location of the
physical endstop switch. However, it's recommended to perform Z
endstop positioning in software with Klipper - once the physical
location of the endstop is in a convenient location, one can make any
further adjustments by running Z_ENDSTOP_CALIBRATE or by manually
updating the Z position_endstop in the configuration file.

# Adjusting bed leveling screws

The secret to getting good bed leveling with bed leveling screws is to
utilize the printer's high precision motion system during the bed
leveling process itself. This is done by commanding the nozzle to a
position nearest each bed screw and then adjusting that screw until
the bed is a set distance from the nozzle. Klipper has a tool to
assist with this. In order to use the tool it is necessary to specify
each screw XY location.

This is done by creating a `[bed_screws]` config section. For example,
it might look something similar to:
```
[bed_screws]
screw1: 100,50
screw2: 100,150
screw3: 150,100
```

If a bed screw is under the bed, then specify the XY position directly
above the screw. If the screw is outside the bed then specify an XY
position closest to the screw that is still within the range of the
bed.

Once the config file is ready, run `RESTART` to load that config, and
then one can start the tool by running:
```
BED_SCREWS_ADJUST
```

This tool will move the printer's nozzle to each screw XY location and
then move the nozzle to a Z=0 height. At this point one can use the
"paper test" to adjust the bed screw directly under the nozzle. See
the information described in
["the paper test"](Bed_Level.md#the-paper-test), but adjust the bed
screw instead of commanding the nozzle to different heights. Adjust
the bed screw until there is a small amount of friction when pushing
the paper back and forth.

Once the screw is adjusted so that a small amount of friction is felt,
run either the `ACCEPT` or `ADJUSTED` command. Use the `ADJUSTED`
command if the bed screw needed an adjustment (typically anything more
than about 1/8th of a turn of the screw). Use the `ACCEPT` command if
no significant adjustment is necessary. Both commands will cause the
tool to proceed to the next screw. (When an `ADJUSTED` command is
used, the tool will schedule an additional cycle of bed screw
adjustments; the tool completes successfully when all bed screws are
verified to not require any significant adjustments.) One can use the
`ABORT` command to exit the tool early.

This system works best when the printer has a flat printing surface
(such as glass) and has straight rails. Upon successful completion of
the bed leveling tool the bed should be ready for printing.

## Fine grained bed screw adjustments

If the printer uses three bed screws and all three screws are under
the bed, then it may be possible to perform a second "high precision"
bed leveling step. This is done by commanding the nozzle to locations
where the bed moves a larger distance with each bed screw adjustment.

For example, consider a bed with screws at locations A, B, and C:

![bed_screws](img/bed_screws.svg.png)

For each adjustment made to the bed screw at location C, the bed will
swing along a pendulum defined by the remaining two bed screws (shown
here as a green line). In this situation, each adjustment to the bed
screw at C will move the bed at position D a further amount than
directly at C. It is thus possible to make an improved C screw
adjustment when the nozzle is at position D.

To enable this feature, one would determine the additional nozzle
coordinates and add them to the config file. For example, it might
look like:
```
[bed_screws]
screw1: 100,50
screw1_fine_adjust: 0,0
screw2: 100,150
screw2_fine_adjust: 300,300
screw3: 150,100
screw3_fine_adjust: 0,100
```

When this feature is enabled, the `BED_SCREWS_ADJUST` tool will first
prompt for coarse adjustments directly above each screw position, and
once those are accepted, it will prompt for fine adjustments at the
additional locations. Continue to use `ACCEPT` and `ADJUSTED` at each
position.