Nozzle Cleaning and First Layer failures
Not asking for help here because I know what the problem is. This is feedback to Prusa so they can hear the pain points with the Prusa XL.
My failures so far are all related to the first layer and "gunk" on the nozzle affecting the auto-levelling. During the heating phase a small amount of material will ooze. Prusa has thought of this so they gently push the nozzle down and it seems they're relying on the softened material pushing out of the way. But this isn't reliable. Every now and then the gunk causes the z-offset to calculate wrong then the first layer becomes a stringy mess rather than a solid sheet.
I didn't have this problem with my first 100+ hours of printing. I think because I was using Prusament which does not ooze much. But for the last 25+ hours of printing I've been using a third-party brand of PLA from Amazon. It oozes quite a bit and sticks to the nozzle very easily. I'm sure this is part of the problem. But within reason I expect the printer to support low-grade PLA.
A simple brush to clean the nozzle would do wonders. I see one design already on printables but it only cleans the nozzle during the parking sequence. I'm not convinced the parking motion alone gives enough cleaning time. A dedicated nozzle-cleaning sequence is needed. I'm not sure why Prusa didn't put a silicone brush on the front-left and g-code between tool changes, like the E3D toolchanger did.
third-party brand of PLA from Amazon. It oozes quite a bit
Make certain the filament is dry.
Cheerio,
RE: Nozzle Cleaning and First Layer failures
Have you seen Surfalex's nozzle scrubber mod:
https://www.printables.com/model/462473-prusa-xl-series-nozzle-scrubber-brush
RE: Nozzle Cleaning and First Layer failures
Actually, the E3d tc didn’t come with anything for prime and wipe either. We all had to develop prime and wipe methods. The E3d intended to explore not only multiple materials, but also different kinds of tools. The XL assumes only one tool design across all the tools.
The red nozzle seal they added to each parking place right before shipping does not wipe at all. It was not intended to.
I would not recommend brushing the nozzle with any kind of metal brush. It can easily damage the oriface of the nozzle. One can use metal brushes pointed perpendicular to the line of string as the nozzle passes by to grab strings or blobs. That works well but like all priming will need to be monitored over time.
What has always worked for me on all my multiple extruder machines is simply a paper towel on the hot nozzle right before I start a print.
RE: Nozzle Cleaning and First Layer failures
Also… the oozing we are seeing is happening for one simple reason; Prusa has the presets way too hot. It doesn’t matter what the make or the materials ALL the material presets are way too high. PLA will do fine at 200c and PETG 205c(you may also want to increase downward cooling for PETG too). This extruder has the heater oriented vertically which changes the shape of the melt zone. As such temps does not need to be set like it is for older style hot blocks.
Also, you may want to try increasing “Retraction on tool disable” to 11.7mm to retract out of the melt zone before the tool moves away from the print to park. This can eliminate the need for a wipe tower with pla. PETG will still need it.
RE: Nozzle Cleaning and First Layer failures
I've had this problem, too. I must mentally remind myself to clean off the tip before it does the auto-leveling. It's very annoying, and if I forget and there's any accumulation when it touches off on the bed, my first layer is hosed.
Aaron