diff --git a/docs/Pressure_Advance.md b/docs/Pressure_Advance.md index 8a849c88..d882b68d 100644 --- a/docs/Pressure_Advance.md +++ b/docs/Pressure_Advance.md @@ -13,58 +13,64 @@ uses the second feature (reducing blobbing during cornering) as a mechanism for tuning. In order to calibrate pressure advance the printer must be configured -and operational. The tuning test involves printing objects and -inspecting the differences between objects. It is a good idea to read -this document in full prior to running the test. +and operational as the tuning test involves printing and inspecting a +test object. It is a good idea to read this document in full prior to +running the test. Use a slicer to generate g-code for the large hollow square found in -[docs/prints/square.stl](prints/square.stl). Use a high speed (eg, -100mm/s) and a coarse layer height (the layer height should be around -75% of the nozzle diameter). It is fine to use a low infill (eg, 10%). +[docs/prints/square_tower.stl](prints/square_tower.stl). Use a high +speed (eg, 100mm/s), zero infill, and a coarse layer height (the layer +height should be around 75% of the nozzle diameter). -Prepare for the test by issuing the following G-Code commands: -`SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=1 ACCEL=500` and -`SET_PRESSURE_ADVANCE ADVANCE_LOOKAHEAD_TIME=0`. These commands make -the nozzle travel slower through corners and they emphasize the -effects of extruder pressure. +Prepare for the test by issuing the following G-Code command: +``` +SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=1 ACCEL=500 +``` +This command makes the nozzle travel slower through corners and to +emphasize the effects of extruder pressure. Then for printers with a +direct drive extruder run the command: +``` +TUNING_TOWER COMMAND=SET_PRESSURE_ADVANCE PARAMETER=ADVANCE START=0 FACTOR=.005 +``` +For long bowden extruders use: +``` +TUNING_TOWER COMMAND=SET_PRESSURE_ADVANCE PARAMETER=ADVANCE START=0 FACTOR=.020 +``` +Then print the object. When fully printed the test print looks like: -For the first print use a pressure advance of zero by running -`SET_PRESSURE_ADVANCE ADVANCE=0.000`. Then print at least 10 layers of -the test object. While the object is printing, make a note of which -direction the head is moving during external perimeters. What many -people see here is blobbing occurring at the corners - extra filament -at the corner in the direction the head travels followed by a possible -lack of filament on the side immediately after that corner: +![tuning_tower](img/tuning_tower.jpg) -![corner-blob](img/corner-blob.jpg) +The above TUNING_TOWER command instructs Klipper to alter the +pressure_advance setting on each layer of the print. Higher layers in +the print will have a larger pressure advance value set. Layers below +the ideal pressure_advance setting will have blobbing at the corners, +and layers above the ideal setting can lead to rounded corners and +poor extrusion leading up to the corner. -This blobbing is the result of pressure in the extruder being released -as a blob when the head slows down to corner. +One can cancel the print early if one observes that the corners are no +longer printing well (and thus one can avoid printing layers that are +known to be above the ideal pressure_advance value). -The next step is to increase pressure advance (start with -`SET_PRESSURE_ADVANCE ADVANCE=0.050`) and reprint the test object. -With pressure advance, the extruder will retract when the head slows -down, thus countering the pressure buildup and ideally eliminate the -blobbing. +Inspect the print and then use a digital calipers to find the height +that has the best quality corners. When in doubt, prefer a lower +height. -If a test run is done with a pressure advance setting that is too -high, one typically sees a dimple in the corner followed by possible -blobbing after the corner (too much filament is retracted during slow -down and then too much filament is extruded during the following speed -up after cornering): +![tune_pa](img/tune_pa.jpg) -![corner-dimple](img/corner-dimple.jpg) +The pressure_advance value can then be calculated as `pressure_advance += + * `. (For example, `0 + 12.90 * +.020` would be `.258`.) -The goal is to find the smallest pressure advance value that results -in good quality corners: - -![corner-good](img/corner-good.jpg) +It is possible to choose custom settings for START and FACTOR if that +helps identify the best pressure advance setting. When doing this, be +sure to issue the TUNING_TOWER command at the start of each test +print. Typical pressure advance values are between 0.050 and 1.000 (the high end usually only with bowden extruders). If there is no significant -improvement after gradually increasing pressure advance to 1.000, then -pressure advance is unlikely to improve the quality of prints. Return -to a default configuration with pressure advance disabled. +improvement with a pressure advance up to 1.000, then pressure advance +is unlikely to improve the quality of prints. Return to a default +configuration with pressure advance disabled. Although this tuning exercise directly improves the quality of corners, it's worth remembering that a good pressure advance @@ -72,8 +78,8 @@ configuration also reduces ooze throughout the print. At the completion of this test, update the extruder's pressure_advance setting in the configuration file and issue a RESTART command. The -RESTART command will also return the acceleration, cornering speeds, -and look-ahead times to their normal values. +RESTART command will clear the test state and return the acceleration +and cornering speeds to their normal values. Important Notes =============== @@ -91,20 +97,16 @@ Important Notes [nozzle temperature](http://reprap.org/wiki/Triffid_Hunter%27s_Calibration_Guide#Nozzle_Temperature) prior to tuning pressure advance. -* It is not unusual for one corner of the test print to be - consistently different than the other three corners. This typically - occurs when the slicer arranges to always change Z height at that - corner. If this occurs, then ignore that corner and tune pressure - advance using the other three corners. - -* Check for warping at the corners during the test prints (the corners - detaching from the bed and rising a small distance upwards during - the print). If one corner appears warped then ignore that corner - when tuning. If significant warping is seen throughout the test then - typical solutions are to reduce the slicer's first layer speed, - adjust the bed temperature, and/or to use the slicer's brim feature. - Pressure advance itself is unlikely to impact warping, but this - tuning test is sensitive to it. +* It is common for the test print to show different behavior on each + corner. Often the slicer will arrange to change layers at one corner + which can result in that corner being significantly different from + the remaining three corners. If this occurs, then ignore that corner + and tune pressure advance using the other three corners. It is also + common for the remaining corners to vary slightly. (This can occur + due to small differences in how the printer's frame reacts to + cornering in certain directions.) Try to choose a value that works + well for all the remaining corners. If in doubt, prefer a lower + pressure advance value. * If a high pressure advance value (eg, over 0.200) is used then one may find that the extruder skips when returning to the printer's diff --git a/docs/img/tune_pa.jpg b/docs/img/tune_pa.jpg new file mode 100644 index 00000000..f8f4d18e Binary files /dev/null and b/docs/img/tune_pa.jpg differ diff --git a/docs/img/tuning_tower.jpg b/docs/img/tuning_tower.jpg new file mode 100644 index 00000000..694b9a50 Binary files /dev/null and b/docs/img/tuning_tower.jpg differ