docs: Update Pressure_Advance.md to use tuning tower
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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@ -13,58 +13,64 @@ uses the second feature (reducing blobbing during cornering) as a
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mechanism for tuning.
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In order to calibrate pressure advance the printer must be configured
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and operational. The tuning test involves printing objects and
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inspecting the differences between objects. It is a good idea to read
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this document in full prior to running the test.
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and operational as the tuning test involves printing and inspecting a
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test object. It is a good idea to read this document in full prior to
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running the test.
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Use a slicer to generate g-code for the large hollow square found in
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[docs/prints/square.stl](prints/square.stl). Use a high speed (eg,
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100mm/s) and a coarse layer height (the layer height should be around
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75% of the nozzle diameter). It is fine to use a low infill (eg, 10%).
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[docs/prints/square_tower.stl](prints/square_tower.stl). Use a high
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speed (eg, 100mm/s), zero infill, and a coarse layer height (the layer
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height should be around 75% of the nozzle diameter).
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Prepare for the test by issuing the following G-Code commands:
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`SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=1 ACCEL=500` and
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`SET_PRESSURE_ADVANCE ADVANCE_LOOKAHEAD_TIME=0`. These commands make
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the nozzle travel slower through corners and they emphasize the
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effects of extruder pressure.
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Prepare for the test by issuing the following G-Code command:
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```
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SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=1 ACCEL=500
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```
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This command makes the nozzle travel slower through corners and to
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emphasize the effects of extruder pressure. Then for printers with a
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direct drive extruder run the command:
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```
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TUNING_TOWER COMMAND=SET_PRESSURE_ADVANCE PARAMETER=ADVANCE START=0 FACTOR=.005
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```
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For long bowden extruders use:
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```
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TUNING_TOWER COMMAND=SET_PRESSURE_ADVANCE PARAMETER=ADVANCE START=0 FACTOR=.020
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```
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Then print the object. When fully printed the test print looks like:
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For the first print use a pressure advance of zero by running
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`SET_PRESSURE_ADVANCE ADVANCE=0.000`. Then print at least 10 layers of
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the test object. While the object is printing, make a note of which
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direction the head is moving during external perimeters. What many
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people see here is blobbing occurring at the corners - extra filament
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at the corner in the direction the head travels followed by a possible
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lack of filament on the side immediately after that corner:
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![tuning_tower](img/tuning_tower.jpg)
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![corner-blob](img/corner-blob.jpg)
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The above TUNING_TOWER command instructs Klipper to alter the
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pressure_advance setting on each layer of the print. Higher layers in
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the print will have a larger pressure advance value set. Layers below
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the ideal pressure_advance setting will have blobbing at the corners,
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and layers above the ideal setting can lead to rounded corners and
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poor extrusion leading up to the corner.
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This blobbing is the result of pressure in the extruder being released
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as a blob when the head slows down to corner.
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One can cancel the print early if one observes that the corners are no
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longer printing well (and thus one can avoid printing layers that are
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known to be above the ideal pressure_advance value).
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The next step is to increase pressure advance (start with
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`SET_PRESSURE_ADVANCE ADVANCE=0.050`) and reprint the test object.
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With pressure advance, the extruder will retract when the head slows
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down, thus countering the pressure buildup and ideally eliminate the
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blobbing.
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Inspect the print and then use a digital calipers to find the height
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that has the best quality corners. When in doubt, prefer a lower
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height.
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If a test run is done with a pressure advance setting that is too
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high, one typically sees a dimple in the corner followed by possible
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blobbing after the corner (too much filament is retracted during slow
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down and then too much filament is extruded during the following speed
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up after cornering):
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![tune_pa](img/tune_pa.jpg)
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![corner-dimple](img/corner-dimple.jpg)
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The pressure_advance value can then be calculated as `pressure_advance
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= <start> + <measured_height> * <factor>`. (For example, `0 + 12.90 *
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.020` would be `.258`.)
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The goal is to find the smallest pressure advance value that results
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in good quality corners:
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![corner-good](img/corner-good.jpg)
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It is possible to choose custom settings for START and FACTOR if that
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helps identify the best pressure advance setting. When doing this, be
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sure to issue the TUNING_TOWER command at the start of each test
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print.
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Typical pressure advance values are between 0.050 and 1.000 (the high
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end usually only with bowden extruders). If there is no significant
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improvement after gradually increasing pressure advance to 1.000, then
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pressure advance is unlikely to improve the quality of prints. Return
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to a default configuration with pressure advance disabled.
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improvement with a pressure advance up to 1.000, then pressure advance
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is unlikely to improve the quality of prints. Return to a default
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configuration with pressure advance disabled.
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Although this tuning exercise directly improves the quality of
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corners, it's worth remembering that a good pressure advance
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@ -72,8 +78,8 @@ configuration also reduces ooze throughout the print.
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At the completion of this test, update the extruder's pressure_advance
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setting in the configuration file and issue a RESTART command. The
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RESTART command will also return the acceleration, cornering speeds,
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and look-ahead times to their normal values.
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RESTART command will clear the test state and return the acceleration
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and cornering speeds to their normal values.
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Important Notes
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===============
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@ -91,20 +97,16 @@ Important Notes
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[nozzle temperature](http://reprap.org/wiki/Triffid_Hunter%27s_Calibration_Guide#Nozzle_Temperature)
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prior to tuning pressure advance.
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* It is not unusual for one corner of the test print to be
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consistently different than the other three corners. This typically
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occurs when the slicer arranges to always change Z height at that
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corner. If this occurs, then ignore that corner and tune pressure
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advance using the other three corners.
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* Check for warping at the corners during the test prints (the corners
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detaching from the bed and rising a small distance upwards during
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the print). If one corner appears warped then ignore that corner
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when tuning. If significant warping is seen throughout the test then
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typical solutions are to reduce the slicer's first layer speed,
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adjust the bed temperature, and/or to use the slicer's brim feature.
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Pressure advance itself is unlikely to impact warping, but this
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tuning test is sensitive to it.
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* It is common for the test print to show different behavior on each
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corner. Often the slicer will arrange to change layers at one corner
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which can result in that corner being significantly different from
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the remaining three corners. If this occurs, then ignore that corner
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and tune pressure advance using the other three corners. It is also
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common for the remaining corners to vary slightly. (This can occur
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due to small differences in how the printer's frame reacts to
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cornering in certain directions.) Try to choose a value that works
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well for all the remaining corners. If in doubt, prefer a lower
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pressure advance value.
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* If a high pressure advance value (eg, over 0.200) is used then one
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may find that the extruder skips when returning to the printer's
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