Missing Layers  

Re: Missing Layers

your filament caught on something during loading never made it down to the extruder, your purge tower is going to be missing a layer as well.
later when it needed a color change again it got lucky and managed to catch the pulley to go down to the extruder.

places to check clean up
1) entrance to the selector body make sure the surface is slightly tapered to give a nice entrance for the filament into the Finda
2) Oil your selector shafts, the selector rides on bushings and they can cause chugging or friction that can slightly change the position of the selector each time it moves. a light plastic safe bearing oil will help just lightly wet the shafts is more then enough.
3) entrance to the extruder body beside the PCB filament sensor. you will need to remove the orange tube and remove the sensor cover and PTFE tube to gain access. you want that area next to the pcb nice and tapered without opening the hole going to the pully. clean it up then put the sensor cap back together with the orange tube removed, open up the tensionar on the side of the extruder to expose the pulley just like you are doing a length calibration on the TPFE turbes. insert some junk pieces of filament with different cuts on the end from blunt to a 45 degree angle and simulate loading by hand, spin the filament around 360 and keep manually loading in and out and spot if the filament catches on anything. you want a smooth load into the pulley. once happy re-assemble but leave the tensionar open and re-calibrate the PTFE lengths again. do each one a couple of times until it loads consistent around the center of the pulley, watch if the filament catches on anything. finish all 5. this will also put the spools filament tension into a ready state. new filament once loaded and unloaded changes the spool position, i like to run a first layer calibration on a filament change so it runs a complete cycle preps the tip for the next color change and pre-tensions the spools.

4)once done put the tensionar back together set the tension between 9-11 Turns of the bolts. (put a mark on the heads to know how many turns you have completed)

at this point you did your best to clean up the load and unload path for all 5 spools from the selector to the extruder.

5) look at some junk filaments you took out from the spools to the selector body, do they have a bunch of chewed half moons in them from the pully assembly up top?
well i find those 5 pulleys need a light touch compared to the extruder. so put a mark on the bolts and reset back to the bolts being flush with the PETG hinge cover.

run some First layer calibrations and keep switching the filament around F1-F5 listen and watch for anything that the filament makes contact with where it cannot move forward or backward. adjust again as needed. once you get clean loads and unloads repeatedly.

setup your test models run 2-3 hours then step up to 15 hour runs.
say a hail mary like i do can't hurt.

most of the time a layer skip is the filament hit something on the way down for load the pulley skipped steps and burned a half moon into the filament the FINDA sees there is filament in the tube so it continues to attempt to print, the filament could even make it down to trick the sensor that something is there in the Extruder but it can't get to the pulley to get into the nozzle. on unload the machine jerks around enough that the upper pully that is stripped just grabs it enough to float it back out and down to the spools that section of filament isn't damage so it can grab it... then on each reload there is a 50/50 shot doe to miss-steps that the filamant didn't hit something and can make it to the extruder.
so you get this hey it didn't skip but then it did skip.

if you get lots of debris on the upper pulleys or you find chips behind the machine take a 1/2 turn off the pulley assembly body bolts/springs and there is a sweet spot in there. keep the tension left and right the same at first but you will find 1,2 need less tension then 3,4,5 so the right side may need a 1/2 or full turn more then the left side.. this is because most of the assembly weight is sitting right on 1,2 as opposed to 3,4,5

Re: Missing Layers

Hi,
Thank you for replying, I may going to try manual loading/calibration again. I also forgot to mention that, during filament change, when the filament being pushed into the extruder, i noticed some motor skipping noise for about 1 second, is this normal or is it that i went too far on the filament calibration?

I did try my best to have filament almost to the center.

Re: Missing Layers

there is some noise but if you feel it is skipping then you should look into why. open the orange tube and run a load unload test see if when the filament just goes in and out of the selector body and out the front that the noise of skipping changes or stays the same. if it improves then the issue is down in the extruder. go through all the clean up as written above and repeat the test with the orange tube connected and see if it is still doing it.

too much or too little spring tension on that pulley body can cause skipping as well. there is a narrow sweet spot.

also make sure the the spring tension in the lid of the assembly body is floating nicely. the PETG bridging in that area clogs the slot that the spring rides in and it can make it too tight because the lid will not float on the springs it will just jam the bolt against the lid body.

Re: Missing Layers

i noticed some motor skipping noise for about 1 second

That's usually speed matching failure. Set the initial load speed in Slic3r to 19 mm/s

Peter

Re: Missing Layers

The motor skipping is after filament goes through the selector tube, if I'm not mistaken, the filament already arrived at the extruder gear and when hitting the extruder gear, mmu motor skipping steps for 1 second, it is not before the selector tube. Sorry about this

Re: Missing Layers

The motor skipping is after filament goes through the selector tube, if I'm not mistaken, the filament already arrived at the extruder gear and when hitting the extruder gear, mmu motor skipping steps for 1 second, it is not before the selector tube. Sorry about this

Yes, that's exactly what is happening. The MMU is pushing the filament at 19mm/3 but the bondtech is only turning at (Slic3r default) 3mm/s.

One or the other will skip unless these speeds are matched and the only one that can be changed is the Bondtech in Slic3r - Filament settings/Advanced/Loading speed at the start.

The Bondtech is much grippier than the MMU, so the MMU skips.

Peter

Re: Missing Layers

I will give that a try @pjr when I got the chance to observe printing process. Thank you for the tip