docs: Add a Manual_Probe.md document

Add information on calibrating the bed on traditional printers with a
Z endstop and bed screws.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Manual_Level.md

@@ -0,0 +1,135 @@
+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.