Pressure advance tuning
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Hello!
I just discovered pressure advance and I'm really happy because my printer had bad blobs on all corners and retraction points. I tweaked it yesterday and today using this python script.
The result was best with a pressure advance of approximately 1.2. If I understood it correctly, this is a really huge amount. Now my corners and top layers are way more beautiful (and I only need 1mm of retraction instead of 8mm to avoid stringing) but the extruder goes back and forth like a maniac and I'm not sure if this is healthy.I'm printing 1.75mm diameter PLA with two Bondtech BMG extruders and a E3D chimera hotend. It has bowdens of 85cm length (it's a rather large printer) but it's capricorn bowden tubes which ought to have less clearance than a regular one. Also the bowden fittings all have a clip inserted to avoid any back and forth movement there.
Is it normal and appropriate for such a setup to require a pressure advance of 1.2? If it isn't, are there some hardware (or software) tweaks to improve the situation?
Thank you for sharing your opinion on this matter!
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@jamkas, I use exactly the same kind of a setup with a BMG clone and a Chimera clone. Pressure advance for a 0.4 mm nozzle, 0.2 mm layer thickness and 0.4 mm layer width for me is 1.0. Note that all the above as well as nozzle temperature will affect the pressure advance setting.
I am about to do a radical hardware 'tweak' .... remove the bowden system, install a direct drive BMG LGX extruder on a Mosquito clone.
For now I have given up on anything with two nozzles - too many issues. I am hoping to set up some sort of lifting mechanism for the use with two nozzles. -
@jamkas said in Pressure advance tuning:
The result was best with a pressure advance of approximately 1.2. If I understood it correctly, this is a really huge amount. Now my corners and top layers are way more beautiful (and I only need 1mm of retraction instead of 8mm to avoid stringing) but the extruder goes back and forth like a maniac and I'm not sure if this is healthy
A figure of 1.2 does not sound crazy to me. there are other factors in play other than the Bowden tube length an internal diameter (although those have a significant influence) There is also the extruder motor, gearing and size of the melt pool + nozzle size that at least theoretically influence PA.
Out of interest can you post some pictures of the test prints showing what they looked like. I am particularity interested in seeing what the best value looked like and how close to perfect it was.
Thanks!
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Thanks for your assurances.
@jens55 I know, two nozzles is a pain sometimes. As the vast majority of my prints only use one filament I also consider ditching it for a single extrusion hotend.@T3P3Tony my printer is still far from perfect. I think it has to many vibrations because I used 6mm cross rods instead of 8mm (It's sort of Ultimaker style). In the future I'm going to fix that and hope for better print quality. The first picture is from the tuning python script with 75mm/s and 5mm/s for the short parts. Bottom is 0.8 pressure advance, top is 2.0. In the second Pic you can still easily see the seam but it's way better than before. Also the top surface layer now is quite flat. Previously it had a lot of over extrusion at the edges. Third picture shows that small structures like the chimney have actually gotten worse a little bit...
Also I noticed that according to my rotating magnet filament monitor the amount of over and under extrusion has worsened a lot. M591 D0 now shows "...min 71% max 139% over 2746.9mm". I used to have "R80:120" as boundary values but had to increase it to "R50:150" and still already got two pauses saying too much motion has been detected.
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The python script is a good data point but it tends to provide very high PA values.
It's a good idea to use a few different means of tuning PA to get a better feel for the actual real world results.
A few other methods are described here: https://duet3d.dozuki.com/Wiki/Pressure_advance#Section_Methods_of_finding_the_right_amount_of_pressure_advance
