From f15cd62587abbeff1fb4a86008432ae58a20161e Mon Sep 17 00:00:00 2001 From: Kevin O'Connor Date: Tue, 11 Sep 2018 11:44:11 -0400 Subject: [PATCH] docs: Update Pressure_Advance.md document Update the document to recommend tuning with decreased acceleration and with square_corner_velocity disabled. Using this approach makes it possible to test with significantly higher pressure advance values. Signed-off-by: Kevin O'Connor --- docs/Pressure_Advance.md | 131 ++++++++++++++++++++++----------------- 1 file changed, 74 insertions(+), 57 deletions(-) diff --git a/docs/Pressure_Advance.md b/docs/Pressure_Advance.md index 9afee00b..7bb694e1 100644 --- a/docs/Pressure_Advance.md +++ b/docs/Pressure_Advance.md @@ -1,36 +1,35 @@ This document provides information on tuning the "pressure advance" -configuration variables for a particular nozzle and filament. The +configuration variable for a particular nozzle and filament. The pressure advance feature can be helpful in reducing ooze. For more information on how pressure advance is implemented see the [kinematics](Kinematics.md) document. -Prerequisites -============= - -In order to tune the pressure advance setting the printer must be -configured and operational. The tuning test involves printing objects -and inspecting the differences between objects. In particular, the -extruder -[E steps](http://reprap.org/wiki/Triffid_Hunter%27s_Calibration_Guide#E_steps) -and -[nozzle temperature](http://reprap.org/wiki/Triffid_Hunter%27s_Calibration_Guide#Nozzle_Temperature) -should be tuned prior to tuning pressure advance. - Tuning pressure advance ======================= Pressure advance does two useful things - it reduces ooze during non-extrude moves and it reduces blobbing during cornering. This guide uses the second feature (reducing blobbing during cornering) as a -mechanism for measuring and tuning the pressure advance configuration. +mechanism for tuning. -Start by changing the extruder section of the config file so that -pressure_advance is set to 0.0. (Make sure to issue a RESTART command -after each update to the config file so that the new configuration -takes effect.) Then print at least 10 layers of a large hollow square -at high speed (eg, 100mm/s). See -[docs/prints/square.stl](prints/square.stl) file for an STL file that -one may use. While the object is printing, make a note of which +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. + +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%). + +Use a low cornering speed during the test by issuing the following +G-Code command: `SET_VELOCITY_LIMIT SQUARE_CORNER_VELOCITY=0 +ACCEL=500`. This will make the nozzle travel slower through corners +and thus emphasize the effects of extruder pressure. + +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 @@ -41,15 +40,13 @@ lack of filament on the side immediately after that corner: This blobbing is the result of pressure in the extruder being released as a blob when the head slows down to corner. -The next step is to set pressure_advance_lookahead_time to 0.0, slowly -increase pressure_advance (eg, start with 0.05), and reprint the test -object. (Be sure to issue RESTART between each config change.) The -goal is to attempt to eliminate the blobbing during cornering. (With -pressure advance, the extruder will retract when the head slows down, -thus countering the pressure buildup and ideally eliminate the -blobbing.) +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. -If a test run is done with a pressure_advance setting that is too +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 @@ -57,41 +54,61 @@ up after cornering): ![corner-dimple](img/corner-dimple.jpg) -The goal is to find the smallest pressure_advance value that results +The goal is to find the smallest pressure advance value that results in good quality corners: ![corner-good](img/corner-good.jpg) -Typical pressure_advance values are between 0.05 and 0.20 (the high +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 seen after increasing pressure_advance to 0.20, then +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. - -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. - -Once a good pressure_advance value is found, return -pressure_advance_lookahead_time to its default (0.010). This parameter -controls how far in advance to check if a head slow-down is -immediately followed by a speed-up - it reduces pointless pressure -changes in the head. It's possible to tune this - higher values will -decrease the number of pressure changes in the nozzle at the expense -of permitting more blobbing during cornering. (Tuning this value is -unlikely to impact ooze.) The default of 10ms should work well on most -printers. +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 -configuration can reduce ooze throughout the print. +configuration also reduces ooze throughout the print. -Finally, once pressure_advance is tuned in Klipper, it may still be -useful to configure a small retract value in the slicer (eg, 0.75mm) -and to utilize the slicer's "wipe on retract option" if available. -These slicer settings may help counteract ooze caused by filament -cohesion (filament pulled out of the nozzle due to the stickiness of -the plastic). It is recommended to disable the slicer's "z-lift on -retract" option. +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 and cornering speeds +to their normal values. + +Important Notes +=============== + +* The pressure advance value is dependent on the extruder, the nozzle, + and the filament. It is common for filament from different + manufactures or with different pigments to require significantly + different pressure advance values. Therefore, one should calibrate + pressure advance on each printer and with each spool of filament. + +* Printing temperature and extrusion rates can impact pressure + advance. Be sure to tune the extruder + [E steps](http://reprap.org/wiki/Triffid_Hunter%27s_Calibration_Guide#E_steps) + and + [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. + +* 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 + normal acceleration. The pressure advance system accounts for + pressure by pushing in extra filament during acceleration and + retracting that filament during deceleration. With a high + acceleration and high pressure advance the extruder may not have + enough torque to push the required filament. If this occurs, either + use a lower acceleration value or disable pressure advance. + +* Once pressure advance is tuned in Klipper, it may still be useful to + configure a small retract value in the slicer (eg, 0.75mm) and to + utilize the slicer's "wipe on retract option" if available. These + slicer settings may help counteract ooze caused by filament cohesion + (filament pulled out of the nozzle due to the stickiness of the + plastic). It is recommended to disable the slicer's "z-lift on + retract" option.