docs: Add Bed_Level.md and Probe_Calibrate.md documents

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

6 files changed, 301 insertions, 18 deletions

diff --git a/docs/Bed_Level.md b/docs/Bed_Level.md
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--- /dev/null
+++ b/docs/Bed_Level.md
@@ -0,0 +1,211 @@
+Bed leveling (sometimes also referred to as "bed tramming") is
+critical to getting high quality prints. If a bed is not properly
+"leveled" it can lead to poor bed adhesion, "warping", and subtle
+problems throughout the print. This document serves as a guide to
+performing bed leveling in Klipper.
+
+It's important to understand the goal of bed leveling. If the printer
+is commanded to a position `X0 Y0 Z10` during a print, then the goal
+is for the printer's nozzle to be exactly 10mm from the printer's
+bed. Further, should the printer then be commanded to a position of
+`X50 Z10` the goal is for the nozzle to maintain an exact distance of
+10mm from the bed during that entire horizontal move.
+
+In order to get good quality prints the printer should be calibrated
+so that Z distances are accurate to within about 25 microns (.025mm).
+This is a small distance - significantly smaller than the width of a
+typical human hair. This scale can not be measured "by eye". Subtle
+effects (such as heat expansion) impact measurements at this scale.
+The secret to getting high accuracy is to use a repeatable process and
+to use a leveling method that leverages the high accuracy of the
+printer's own motion system.
+
+# Choose the appropriate calibration mechanism
+
+Different types of printers use different methods for performing bed
+leveling. All of them ultimately depend on the "paper test" (described
+below). However, the actual process for a particular type of printer
+is described in other documents.
+
+Prior to running any of these calibration tools, be sure to run the
+checks described in the [config check document](Config_checks.md). It
+is necessary to verify basic printer motion before performing bed
+leveling.
+
+For printers with an "automatic Z probe" be sure to calibrate the
+probe following the directions in the
+[Probe Calibrate](Probe_Calibrate.md) document. For delta printers,
+see the [Delta Calibrate](Delta_Calibrate.md) document.
+
+During calibration it may be necessary to set the printer's Z
+`position_min` to a negative number (eg, `position_min = -2`). The
+printer enforces boundary checks even during calibration
+routines. Setting a negative number allows the printer to move below
+the nominal position of the bed, which may help when trying to
+determine the actual bed position.
+
+# The "paper test"
+
+The primary bed calibration mechanism is the "paper test". It involves
+placing a regular piece of "copy machine paper" between the printer's
+bed and nozzle, and then commanding the nozzle to different Z heights
+until one feels a small amount of friction when pushing the paper back
+and forth.
+
+It is important to understand the "paper test" even if one has an
+"automatic Z probe". The probe itself often needs to be calibrated to
+get good results. That probe calibration is done using this "paper
+test".
+
+In order to perform the paper test, cut a small rectangular piece of
+paper using a pair of scissors (eg, 5x3 cm). The paper generally has a
+width of around 100 microns (0.100mm). (The exact width of the paper
+isn't crucial.)
+
+The first step of the paper test is to inspect the printer's nozzle
+and bed. Make sure there is no plastic (or other debris) on the nozzle
+or bed.
+
+**Inspect the nozzle and bed to ensure no plastic is present!**
+
+If one always prints on a particular tape or printing surface then one
+may perform the paper test with that tape/surface in place. However,
+note that tape itself has a width and different tapes (or any other
+printing surface) will impact Z measurements. Be sure to rerun the
+paper test to measure each type of surface that is in use.
+
+If there is plastic on the nozzle then heat up the extruder and use a
+metal tweezers to remove that plastic. Wait for the extruder to fully
+cool to room temperature before continuing with the paper test. While
+the nozzle is cooling, use the metal tweezers to remove any plastic
+that may ooze out.
+
+**Always perform the paper test when both nozzle and bed are at room
+temperature!**
+
+When the nozzle is heated, its position (relative to the bed) changes
+due to thermal expansion. This thermal expansion is typically around a
+100 microns, which is about the same width as a typical piece of
+printer paper. The exact amount of thermal expansion isn't crucial,
+just as the exact width of the paper isn't crucial. Start with the
+assumption that the two are equal (see below for a method of
+determining the difference between the two widths).
+
+It may seem odd to calibrate the distance at room temperature when the
+goal is to have a consistent distance when heated. However, if one
+calibrates when the nozzle is heated, it tends to impart small amounts
+of molten plastic on to the paper, which changes the amount of
+friction felt. That makes it harder to get a good calibration.
+Calibrating while the bed/nozzle is hot also greatly increases the
+risk of burning oneself. The amount of thermal expansion is stable, so
+it is easily accounted for later in the calibration process.
+
+**Use an automated tool to determine precise Z heights!**
+
+Klipper has several helper scripts available (eg, MANUAL_PROBE,
+Z_ENDSTOP_CALIBRATE, PROBE_CALIBRATE, DELTA_CALIBRATE). Choose one of
+them and follow the directions in the documents described above.
+
+Run the appropriate command in the OctoPrint terminal window. The
+script will prompt for user interaction in the OctoPrint terminal
+output. It will look something like:
+```
+Recv: // Starting manual Z probe. Use TESTZ to adjust position.
+Recv: // Finish with ACCEPT or ABORT command.
+Recv: // Z position: ?????? --> 5.000 <-- ??????
+```
+
+The current height of the nozzle (as the printer currently understands
+it) is shown between the "--> <--". The number to the right is the
+height of the last probe attempt just greater than the current height,
+and to the left is the last probe attempt less than the current height
+(or ?????? if no attempt has been made).
+
+Place the paper between the nozzle and bed. It can be useful to fold a
+corner of the paper so that it is easier to grab. (Try not to push
+down on the bed when moving the paper back and forth.)
+
+![paper-test](img/paper-test.jpg)
+
+Use the TESTZ command to request the nozzle to move closer to the
+paper. For example:
+```
+TESTZ Z=-.1
+```
+
+The TESTZ command will move the nozzle a relative distance from the
+nozzle's current position. (So, `Z=-.1` requests the nozzle to move
+closer to the bed by .1mm.) After the nozzle stops moving, push the
+paper back and forth to check if the nozzle is in contact with the
+paper and to feel the amount of friction. Continue issuing TESTZ
+commands until one feels a small amount of friction when testing with
+the paper.
+
+If too much friction is found then one can use a positive Z value to
+move the nozzle up. It is also possible to use `TESTZ Z=+` or `TESTZ
+Z=-` to "bisect" the last position - that is to move to a position
+half way between two positions. For example, if one received the
+following prompt from a TESTZ command:
+```
+Recv: // Z position: 0.130 --> 0.230 <-- 0.280
+```
+Then a `TESTZ Z=-` would move the nozzle to a Z position of 0.180
+(half way between 0.130 and 0.230). One can use this feature to help
+rapidly narrow down to a consistent friction. It is also possible to
+use `Z=++` and `Z=--` to return directly to a past measurement - for
+example, after the above prompt a `TESTZ Z=--` command would move the
+nozzle to a Z position of 0.130.
+
+After finding a small amount of friction run the ACCEPT command:
+```
+ACCEPT
+```
+This will accept the given Z height and proceed with the given
+calibration tool.
+
+The exact amount of friction felt isn't crucial, just as the amount of
+thermal expansion and exact width of the paper isn't crucial. Just try
+to obtain the same amount of friction each time one runs the test.
+
+If something goes wrong during the test, one can use the `ABORT`
+command to exit the calibration tool.
+
+# Determining Thermal Expansion
+
+After successfully performing bed leveling, one may go on to calculate
+a more precise value for the combined impact of "thermal expansion",
+"width of the paper", and "amount of friction felt during the paper
+test".
+
+This type of calculation is generally not needed as most users find
+the simple "paper test" provides good results.
+
+The easiest way to make this calculation is to print a test object
+that has straight walls on all sides. The large hollow square found in
+[docs/prints/square.stl](prints/square.stl) can be used for this.
+When slicing the object, make sure the slicer uses the same layer
+height and extrusion widths for the first level that it does for all
+subsequent layers. Use a coarse layer height (the layer height should
+be around 75% of the nozzle diameter) and do not use a brim or raft.
+
+Print the test object, wait for it to cool, and remove it from the
+bed. Inspect the lowest layer of the object. (It may also be useful to
+run a finger or nail along the bottom edge.) If one finds the bottom
+layer bulges out slightly along all sides of the object then it
+indicates the nozzle was slightly closer to the bed then it should
+be. One can issue a `SET_GCODE_OFFSET Z=+.010` command to increase the
+height. In subsequent prints one can inspect for this behavior and
+make further adjustment as needed. Adjustments of this type are
+typically in 10s of microns (.010mm).
+
+If the bottom layer consistently appears narrower than subsequent
+layers then one can use the SET_GCODE_OFFSET command to make a
+negative Z adjustment. If one is unsure, then one can decrease the Z
+adjustment until the bottom layer of prints exhibit a small bulge, and
+then back-off until it disappears.
+
+The easiest way to apply the desired Z adjustment is to create a
+START_PRINT g-code macro, arrange for the slicer to call that macro
+during the start of each print, and add a SET_GCODE_OFFSET command to
+that macro. See the [slicers](Slicers.md) document for further
+details.
diff --git a/docs/Config_checks.md b/docs/Config_checks.md
index 69c30462..fb7cd852 100644
--- a/docs/Config_checks.md
+++ b/docs/Config_checks.md
@@ -152,16 +152,13 @@ command is: `PID_CALIBRATE HEATER=heater_bed TARGET=60`
 ### Next steps
 
 This guide is intended to help with basic verification of pin settings
-in the Klipper configuration file. It may be necessary to perform
-detailed printer calibration - a number of guides are available online
-to help with this (for example, do a web search for "3d printer
-calibration").
-
-See the [Slicers](Slicers.md) document for information on configuring
-a slicer with Klipper. If one is using traditional endstop switches
-with Trinamic stepper motor drivers then see the
-[Endstop Phase](Endstop_Phase.md) document. If using a delta printer,
-see the [Delta Calibrate](Delta_Calibrate.md) document.
+in the Klipper configuration file. Be sure to read the
+[bed leveling](Bed_Level.md) guide. Also see the [Slicers](Slicers.md)
+document for information on configuring a slicer with Klipper.
 
 After one has verified that basic printing works, it is a good idea to
 consider calibrating [pressure advance](Pressure_Advance.md).
+
+It may be necessary to perform other types of detailed printer
+calibration - a number of guides are available online to help with
+this (for example, do a web search for "3d printer calibration").
diff --git a/docs/Delta_Calibrate.md b/docs/Delta_Calibrate.md
index 528021a9..2729fa49 100644
--- a/docs/Delta_Calibrate.md
+++ b/docs/Delta_Calibrate.md
@@ -9,6 +9,11 @@ them manually. In contrast, the software calibration code can provide
 excellent results with just a few minutes of time. No special probing
 hardware is necessary to get good results.
 
+Ultimately, the delta calibration is dependent on the precision of the
+tower endstop switches. If one is using Trinamic stepper motor drivers
+then consider enabling [endstop phase](Endstop_Phase.md) detection to
+improve the accuracy of those switches.
+
 Basic delta calibration
 =======================
 
@@ -35,13 +40,14 @@ calibration completes, one can remove this setting from the config.)
 There are two ways to perform the probing - manual probing and
 automatic probing. Automatic probing utilizes a hardware device
 capable of triggering when the toolhead is at a set distance from the
-bed. Manual probing involves using the "paper test" to determine the
-height at each probe point. It is recommended to use manual probing
-for delta calibration. A number of common printer kits come with
-probes that are not sufficiently accurate (specifically, small
-differences in arm length can cause effector tilt which can skew an
-automatic probe). Manual probing only takes a few minutes and it
-eliminates error introduced by the probe.
+bed. Manual probing involves using the
+["paper test"](Bed_Level.md#the-paper-test) to determine the height at
+each probe point. It is recommended to use manual probing for delta
+calibration. A number of common printer kits come with probes that are
+not sufficiently accurate (specifically, small differences in arm
+length can cause effector tilt which can skew an automatic
+probe). Manual probing only takes a few minutes and it eliminates
+error introduced by the probe.
 
 To perform the basic probe, make sure the config has a
 [delta_calibrate] section defined and run:
@@ -56,7 +62,7 @@ SAVE_CONFIG
 ```
 
 The basic calibration should provide delta parameters that are
-accurate enough for basic printing.  If this is a new printer, this is
+accurate enough for basic printing. If this is a new printer, this is
 a good time to print some basic objects and verify general
 functionality.
 
diff --git a/docs/Overview.md b/docs/Overview.md
index ce69e513..30b3c768 100644
--- a/docs/Overview.md
+++ b/docs/Overview.md
@@ -14,6 +14,9 @@ as a reference for the config file. See the [Slicers](Slicers.md)
 document for information on configuring a slicer with Klipper. See the
 [Endstop Phase](Endstop_Phase.md) document for information on
 Klipper's "stepper phase adjusted endstop" system. See the
+[Bed Level](Bed_Level.md) document for information on bed leveling
+with Klipper. See the [Probe Calibrate](Probe_Calibrate.md) document
+for information on calibrating automatic Z probes. See the
 [Delta Calibrate](Delta_Calibrate.md) document for information on
 calibrating delta printers. The
 [Pressure Advance](Pressure_Advance.md) document contains information
diff --git a/docs/Probe_Calibrate.md b/docs/Probe_Calibrate.md
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+++ b/docs/Probe_Calibrate.md
@@ -0,0 +1,66 @@
+This document describes the method for calibrating the x, y, and z
+offsets of an "automatic z probe" in Klipper. This is useful for users
+that have a `[probe]` or `[bltouch]` section in their config file.
+
+# Calibrating probe X and Y offsets
+
+To calibrate the X and Y offset, navigate to the OctoPrint "Control"
+tab, home the printer, and then use the OctoPrint jogging buttons to
+move the head to a position near the center of the bed.
+
+Place a piece of blue painters tape (or similar) on the bed underneath
+the probe. Navigate to the OctoPrint "Terminal" tab and issue a PROBE
+command:
+```
+PROBE
+```
+Place a mark on the tape directly under where the probe is (or use a
+similar method to note the location on the bed).
+
+Issue a `GET_POSITION` command and record the toolhead XY location
+reported by that command. For example if one sees:
+```
+Recv: // toolhead: X:46.500000 Y:27.000000 Z:15.000000 E:0.000000
+```
+then one would record a probe X position of 46.5 and probe Y position
+of 27.
+
+After recording the probe position, issue a series of G1 commands
+until the nozzle is directly above the mark on the bed. For example,
+one might issue:
+```
+G1 F300 X57 Y30 Z15
+```
+to move the nozzle to an X position of 57 and Y of 30. Once one finds
+the position directly above the mark, use the `GET_POSITION` command
+to report that position. This is the nozzle position.
+
+The x_offset is then the `nozzle_x_position - probe_x_position` and
+y_offset is similarly the `nozzle_y_position - probe_y_position`.
+Update the printer.cfg file with the given values, remove the
+tape/marks from the bed, and then issue a `RESTART` command so that
+the new values take effect.
+
+# Calibrating probe Z offset
+
+Providing an accurate probe Z offset is critical to obtaining high
+quality prints.
+
+Start by homing the printer and then move the head to a position near
+the center of the bed. Navigate to the OctoPrint terminal tab and run
+the `PROBE_CALIBRATE` command to start Klipper's probe calibration
+tool.
+
+This tool will perform an automatic probe, then lift the head, move
+the nozzle over the location of the probe point, and start the manual
+probe tool. Once the manual probe tool starts, perform the
+["paper test"](Bed_Level.md#the-paper-test) to determine the actual
+nozzle height at the given point.
+
+If the nozzle does not move to a position above the probe point, then
+`ABORT` the manual probe tool and perform the XY probe offset
+calibration described above.
+
+After completing the "paper test", use the `ACCEPT` command to
+accept the current Z height and then use the `SAVE_CONFIG` command to
+save the given probe z_offset to the config file.
diff --git a/docs/img/paper-test.jpg b/docs/img/paper-test.jpg
new file mode 100644
index 00000000..3fabbad2
--- /dev/null
+++ b/docs/img/paper-test.jpg