Silk PLA Stuck Filament Detection  

RE: Silk PLA Stuck Filament Detection

The stuck filament detection in the print head is glitchy at best. With silky and matte filaments and everything that's a bit flexy it is terrible. I think the higher surface tension of the molten filament leads to odd values that don't fit the profile they use internally for PLA. Honestly I think this was a feature they thought they can easily implement with the existing load cell, but irl it's way too complex. It needs another type of sensor.

I suggest just switching it off, you'll ruin more prints with false positives than you'll save. The only real causes I've ever seen were with damaged filaments, in which case there was anyway nothing I could do but restart with a new spool (or it would just trigger again and again). At least on newer firmwares it stopped shutting down the bed, restarting at different print height or cooking the filament in the nozzle 😉

RE: Silk PLA Stuck Filament Detection

Thanks for the info! I have been trying to figure it out and testing different stuff. If I don't do a color change, it's much better. If I do any color changes with that type of filament, I get the stuck filament detection. I do get some clicking when I try to unload and load. I'm not sure if that's from the detection creating the problem or not. The notes about the restarting at different heights and cooking the filament are good to know! I have seen where it overheats and looks a bit cooked after a jam detection. I'll check and update our firmware. I also read running it a little hotter (230C) helps a lot too for the higher speed printers.

Appreciate the help!

RE:

I would advise against printing silk filament any hotter than necessary. It will jam and it's a pain to clear out of the heatbreak.
Run a temp tower, the optimal temperatures for different silk PLA can vary quite a lot (I've seen 190 to 215°C). Then use the lowest feasible temperature.

You can check how it looks when extruding the first few cm after a filament change: Typically it will form a blob instead of a string and look like it wants to crawl back into the nozzle. This is due to high surface tension. You might also notice that it stays hot/squishy a lot longer than regular PLA (= burnt fingers when ripping off the string). The unloading problems come from there, and are typical (at least I get them with all silk PLA I tried). Unloading does a heatup and purge, followed by a very fast/long retract. Normally this leads to less filament in the melt zone, but with silk PLA some of it gets sucked back into the nozzle. This causes too much& too hot filament getting in the heatbreak, where it's still too soft and sticks to the walls. This is where the resistance builds up that's causing the clicking.

Also with the current fw you can switch off stuck filament detection per tool (i.e. just switch it off for problematic filament).

I would advise against printing silk filament or any foaming filament unless you have an overwhelming need for it.

Users think PLA is a simple-to-print filament and regular PLA is - but foaming filament of any type should be considered a technical challenge. 

It is unfortunate that foaming PLA has been tagged 'silk' by the manufacturers as it suggests the difference is purely cosmetic, it isn't.  It does have a place as a lightweight engineering material where density matters (and foaming TPE has a place when the ability to vary the flexibility matters) but it's semi-controlled expansion, thermal resistance and changes in strength and resilience mean that it's always going to be tricky to use and newbies should be made aware that it's going need a couple of years experience before attempting it.

If you just want the cosmetic effect then it's often easier to print regular PLA and give it a careful, multi-coat, spray-paint finish.

Cheerio,

RE: Silk PLA Stuck Filament Detection

Thanks @ntdesign that's a super helpful explanation. I have noticed that when the silk filament purges from the nozzle. I plan to do a temp tower and try to tune it in a bit better. Any idea if the XL does a longer retraction between color changes when it docks the head? I feel like if I just print single color silk prints I don't see this issue, but if there are color changes I do. I'm curious if there are some retraction settings for color changes or anything else that could help. I would turn off the warning, but that clicking when unloading reloading is what made me want to be sure I'm not masking an issue that will cause a problem later. Good to know you can turn off the stuck filament detection per head in the latest firmware. I like a lot of the XL features like that. I like to load backup filament in extra heads for longer prints where I know I'm going to run out so the print keeps going.  I've also read it's a good idea to purge the nozzle for a bit with some standard PLA or PETG after to help clean the head. 

@Diem - yeah, I have read up a bit more on the silk PLA's and some of these more cosmetic ones in general. They definitely get marketed like any other PLA and definitely are not. I print mainly for fun and been really trying to learn as I go. I rarely print with any silk or filled filaments. I like to try and take these failures as a chance to try and learn more about the technical side of printing, what the root of the issue was, and how to do it better in the future. We also have these printers in our company's maker space and I'm hoping to help others from making the same mistakes. I am looking at other options like rub n buff to give the metallic effect in this case. I'm sure that process will come with more learning and mistakes 🤣 

Before using rub n buff you need to get a smooth surface; use wet and dry paper wet, by hand, or you risk friction-melting the surface.

You might need a coat of primer with some filaments.

Cheerio,

RE: Silk PLA Stuck Filament Detection

Well, based to the extruder motor noises I think it only retracts into the nozzle. It's not really necessary to pull it all the way up, cooking it will not have any effect in the short time it takes to reach parking temperature. For nice finish you'll anyway need a wipe tower to get back to optimal nozzle pressure, and this would clear the meltzone of degraded material if there is any.
I'm pretty sure PR know that some filaments don't unload cleanly, after all there's a prompt during each manual filament swap asking if it worked.

Try the lowest possible temp first, if the clicking goes away you're set. Another reason could be too high tension on the springs, mine were tensioned way too much out of factory. Some material including silk PLA might still be a bit soft at the gear, and too much tension can deform the filament causing issues in the heatbreak when it goes back in. In my case it was a couple of full turns on 4 of 5 tools until they were reasonably tensioned, the remaining one was fine.
Note: I'm using Obxidian, it can be a different story with brass nozzles. The coating goes a long way to prevent sticking filament and damage from cooking.
Generally, if the temp is dialled in for the specific brand I don't have any extra problems with silk PLA. It sticks well to other PLA, but not well enough to PETG to be useful as supports. And of course stuck filament detection needs to be off.