LINEAR ADVANCE_MK2/mmu
Hi,
i tried to set LA. After flashing new firmware "RC2",i did an extruder calibration, then follow this https://mattshub.com/2017/10/02/linear-advance/ to find the right "K" value. Afterwards,for my own files, I will use Slicer PE/mmu.
As the "K test file" is set on the right side where my bed is "going down" , i change the X/Y value to center it on the bed. Then...i decided to re-do my bed level calibration anyway. As the print test is based on the regularity of the width (?), i thought a wrong bed would degrade the result.
After a nice one-layer square print with normal setup, i re-did the "K test file" to find the "k" value (see picture).
All lines seem nice between 200-300, maybe better somewhere in the average value...but correct. Over 340, it seems to degrade, as well as below 200.
Then, i did several try printing with speed at 80mm/s, or 100, changing my K value from 200 to 300. I got 2 "problems" that were consistent :
- lines width tends not being regular, making the surface ugly
- on the corners or turns (where it "slows down") , and on beginning and end of lines : missing material = holes...
I have misunderstand something, the "K test file"make nice line, and my print test not...See one of my try :
I try to reduce retraction from 4 to 2mm. Line width from 0,35 to 0,45mm. Flow +/- 20%...Only reducing speed to 50 or 60mms seems to improve, but then, LA is no point ?
Where i get wrong ?
Anybody have try it and get good & nice surface at 100mm/s ? What parameter you would adjust ?
Have a nice day !
Re: LINEAR ADVANCE_MK2/mmu
Linear Advance will only affect the very start and end of the paths; the centre of the paths will not be changed.
I did some testing and came up with a value of 470 - basically looking at the seam and the corners of a test cube with K value changing on every layer.
Then when I printed some real models, I needed to halve the K value from the test cube.
I need to do a lot more work on this, but for now I have turned it off and let the slicer do the calculations for seam hiding.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: LINEAR ADVANCE_MK2/mmu
Thanks sharing your experience. i'll do more test in the coming weeks and let you know if i get good result. As i mostly print with ASA, it might not ease the process at 100mm/s...but who knows ?
Re: LINEAR ADVANCE_MK2/mmu
I think retraction is supposed to be very low when using Linear Advance. Almost zero. Maybe 0.5mm or less.
Also, make sure your extrusion amount is calibrated correctly, FIRST. There should be an explanation in the manual how to calibrate prusa extrusion.
For example, if your extrusion is using 105mm of filament when it should only use 100mm filament, Linear Advance will have no effect or get worse result.
Re: LINEAR ADVANCE_MK2/mmu
It's true that your printer (esteps/mm, ..) should be quite good calibrated before playing with LIN_Advance. Else you will have a hard time finding out why it prints bad. But retraction length will not harm your print, as the retraction isn't influenced by LIN_Advance. It only kicks in during moves that have E and at elast X or Y distance in it.
Looking at your picture, first I have to repeat what PJR stated above. The wavy straight infill lines are not affected by LIN_Advance.
The errors in the circles will only be influenced when you hit the perfomance limit of the ATMega controler or the gcode transfer speed from USB or SD-card (which will most likely not be the issue), which you never should. Have you tried this model at such speeds before? If you get stuttering or slowing down during the arcs, you are trying to process more gcode lines / second than the ATMega can handle. Possible work arounds are slowing down print speed or reduce the resolution of your stl file.
I wrote LIN_Advance mainly to improve the print quality. While this means you can go faster when you only want to keep the usual print quality, you still have to keep the volumetric flow limit of you heat block in mind, also the processing power which is in fact impacted by active LIN_Advance.
Re: LINEAR ADVANCE_MK2/mmu
also the processing power which is in fact impacted by active LIN_Advance.
Hi Sebastian
Thank you cor coming up with this and getting a decent algorithm in place.
The processing power of the RAMBo is my biggest concern, and has been for some time now; this is one of the reasons why I am not currently using Linear Advance, but rather employing the PreloadVE of KISS. Unfortunately this is only effective at the start and end of paths, but does seem to work well.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: LINEAR ADVANCE_MK2/mmu
In fact I nearly never run into processing power limits with reasonable models even with LIN_Advance. I think the main problem is more that some people don't think about their stl resolution and/or don't know how to control this in the design environment - it's worth nothing to have one triangle point every 0,001mm when we print on a machine which will reach 0,01-0,05mm resolution if we are lucky.
I was also using Slic3rs pressure control feature bevor I started "LA". But it's a very rough method, and even the long existing old ADVANCE feature from Marlin did a slightly better job with low overhead cycles. Therefore if you want a fast aproximation, you might look into that one.
For furture printers, I guess we will see much more powerful boards. Then we should be able to do much more cool quality improving stuff, like S-shaped acceleration curves 😎
Re: LINEAR ADVANCE_MK2/mmu
Thanks to lighten LA.
Extruder is calibrated, that was my first step before trying LA.
I've done test on small files, like a one layer 30x30 square, and result looks the same.
I will try to make some more test, printing at normal speed, as i did mostly 100mm/s test. If i reach a nice layer looking, then i will increase speed.