Anycubic Mega S -- extrusion woes - Page 1
Forum section: electronics / general

author: ebastler
author_rank: Super Contributor
timestamp: October 26, 2024, 08:37:03 am
content: I use 3D printing sporadically, to make some small enclosures or mechanical adapters. Using an Anycubic Mega S, a simple bed-slinger printer with filament supply through a Bowden tube. After replacing the stepper drivers with Trinamic modules and fixing the bent guide rods for the stage early on, I am quite happy with its XYZ mechanics. Positioning seems precise (but slow), bed levelling is straightforward and remains stable for a long time.But I always struggle with the filament supply to the nozzle. It seems to be "lagging behind":When the printer deposits the fat trace at the beginning of a new print (at the front edge of the stage, to prime the print head), the first 5 cm or more never get filament flow -- even if I have printed just before.When it then moves over to the actual print, the first few cm get deposited with the excessive flow from the priming trace.During the print, filament flow is stable as long as the printer lays down a continuous trace. When it moves to a different place, there is some light stringing of the filament, and -- more annoying -- the first few cm deposited at the new location are again missing or under-dosed.Is this just a question of setting the proper retraction values, or is there excessive friction in the Bowden tube or a problem with the extruder gear or adjustment? EDIT: Or a partially clogged nozzle maybe?I am using PrusaSlicer 2.8.1, with the default settings for the Anycubic Mega series. Have played with retraction length and speed but could not achieve a significant improvement yet. Material is plain PLA (eSUN PLA+ most recently).Are there any tricks (special test prints maybe) for approaching the settings optimization systematically? Anything to look for in the filament supply mechanism, to diagnose Bowden or extruder problems? Many thanks for pointing me in the right direction!

author: Ian.M
author_rank: Super Contributor
timestamp: October 26, 2024, 09:25:42 am
content: Absorbed moisture in your PLA can do this - steam bubbles form in the hot end and cushion filament movement so it doesn't immediately result in extrusion/retraction. Also look for any slop in your bowden tube end fittings - if they've worn the tube where they grip it, cut a little off the end to get a fresh grip.

author: MarkF
author_rank: Super Contributor
timestamp: October 26, 2024, 09:27:38 am
content: Before you get carried away doing a bunch of adjustments and tweeks, insure that your printer is properly calibrated. Do each of the X, Y and extruder axis as shown in this video. Especially step #3 since you're worried about the extrusion.To begin a print, I have added some custom g-code to print a line of filament along the left side of the build plate to prime the nozzle. My Creality CR10 never prints the first little also. (For the Prusaslicer, this goes in the 'Printer Settings' tab.) Some slicers do this by printing a skirt first, which I never liked.My end g-code moves the build plate to the front and the nozzle centered at the back for easy print removal.MY START G-CODE:Code:;G90 ;use absolute coordinatesM83 ;extruder relative modeG28 ;home all axisG92 E0 ;reset extruderG0 Z10.00 F600 ;move z-axis upM140 S{first_layer_bed_temperature} ;set bed temperatureM105 ;report temperaturesM190 S{first_layer_bed_temperature} ;wait for bed temperature to stabilizeM104 S{first_layer_temperature} ;set hotend temperatureM105 ;report temperaturesM109 S{first_layer_temperature} ;wait for hotend temperature to stabilize; Prime nozzleG0 X10.1 Y20.0 Z0.20 F6000 ;move to start positionG1 X10.1 Y200.0 Z0.20 F1500 E20 ;draw the first lineG0 X10.4 Y200.0 Z0.20 F6000 ;move to the side a littleG1 X10.4 Y80.0 Z0.20 F1500 E8 ;draw the second lineG0 Z5.00 F6000 ;move z-axis up, 1st shearing actionG0 X10.4 Y110.0 F6000 ;move y-axis, 2nd shearing actionG92 E0 ;reset extruder;MY END G-CODE:Code:;{if max_layer_z+2 < max_print_height}G1 Z{max_layer_z+2} F600 ;move print head up {endif}{if max_layer_z+20 < max_print_height}G1 Z{max_layer_z+20} F600 ;move print head further up {endif}G0 X150 Y200 F6000 ;present printM140 S0 ;turn off bedM104 S0 ;turn off hotendM107 ;turn off fanM84 X Y E ;disable motorsM42 P27 S255 ;buzzer onM0 S2 ;delay 2secM42 P27 S0 ;buzzer off;

author: ebastler
author_rank: Super Contributor
timestamp: October 26, 2024, 10:21:45 am
content: Thank you both!Quote from: Ian.M on October 26, 2024, 09:25:42 amWould steam bubbles typically appear as a steady effect, or more as sporadic events? It seems that the filament "lag" is pretty consistent and reproducible for me. The filament has been on the shelf for a while, and I have not tried baking it. Had it stored under normal room conditions, not a damp basement or such.The bowden tube ends look alright, I think. I had trimmed the tube a bit a while ago since it seemed longer than necessary, and hence had a stronger bend.Quote from: MarkF on October 26, 2024, 09:27:38 amI checked the extruder calibration last year, and it seems good. Passed the test, and also I get nice layers as long as everything is deposited continuously without breaks.As mentioned, the PrusaSlicer does do a priming trace at the beginning, with a higher-than-normal extrusion rate. It is long enough to get the filament flowing reliably, but it's noticeable that there is always a dead time at the beginning. I also let it print a thin skirt, which serves to take up the unwanted "tail end" of the extrusion at a higher rate, so it does not mess up the print itself.The delayed onset and end of the "fat" priming trace do not bother me per se. But they are indicative of what continues to happen later during regular printing: Whenever the print head has to move elsewhere and interrupt deposition, filament supply to the nozzle continues after it should end, and then restarts later than it should.

author: MarkF
author_rank: Super Contributor
timestamp: October 26, 2024, 10:39:15 am
content: That reminds me...I just replaced the brass gear on the extruder motor. The teeth looked a little worn after several years. I went with a stainless steel one this go around. (The new gear DID change my calibration.)I also went with a little larger (ID: 2.0mm) Capricorn bowden tube for a little more clearance and less friction.1 Meter SOLID RED 1.75mm Bowden Tubing

author: ebastler
author_rank: Super Contributor
timestamp: October 26, 2024, 12:44:17 pm
content: I took the filament supply train apart to take a closer look. The bowden tube is solidly clamped in place and the filament moves through with little friction. The extruder leaves a nice, evenly-spaced sequence of indents on the filament, without noticeable tearing or double-indents -- which I hope implies that it transports the filament as intended.However I did notice that the inside of the brass extruder tip was not clear. I had "cold-pulled" the filament back out of it after the printer had fully cooled down, and got a nice conical end on the filament -- which I always though to imply that the molten filament had been fully removed from the tip. But found the inner walls of the tip to be coated with another layer of filament -- maybe PTEG from earlier prints, with a higher melting point?I will order some replacement tips to rule out the possibility of a clogged tip. Will also try some systematic retraction adjustments with a "retraction tower".I am tempted to try a conversion to direct extrusion, by mounting the existing extruder directly on the print head. Worst side effect that might have is to slow down the X axis somewhat, right?

author: Ian.M
author_rank: Super Contributor
timestamp: October 26, 2024, 01:19:36 pm
content: The steam bubbles from filament with moderately high moisture content usually wont coalesce to form a steam pocket in the nozzle due to the viscosity of the plastic and the limited time they have to merge*. Instead they partially foam the plastic in the nozzle chamber, so your extruder is effectively pushing on a sponge! The moisture level will be fairly consistent over the whole length of filament used in a print as it will have seen pretty much the same conditions on the spool for the same length of time since you opened the sealed pack so the extrude/retract problems will be persistent and fairly consistent, until you change to a spool with a different moisture content.Therefore try drying your filament - weighing the spool before and after drying to assess how much moisture has been removed or try a freshly opened spool of good quality filament and see if your extrude/retract problems go away or at least vastly improve. Don't exceed the glass transition temperature when drying filament!* If its wet enough to hear popping as it passes through the nozzle or see surface bubbles if you extrude a string hanging straight down, its way past the point where foaming can cause extrusion/retraction issues.