Nozzle wiping, PETG



  • I have implemented a nozzle wiping station on the far right of my X axis.
    There is about a 1 mm height interference between the nozzle and a silicone wiper blade.
    The wiping happens very nicely but the dregs attach themselves to the nozzle shoulder.

    For those of you who have implemented nozzle wiping, how have you managed to overcome the habit of PETG to stick to the nozzle and migrating up the nozzle.

    I can not travel diagonally over the wiper as only the x axis does the wiping. I can not situate the wiper diagonally as I do not have enough travel room.

    Thoughts? Tricks that you have discovered ?



  • @jens55 Your options are a bit limited as you can't travel and wipe. Try a 1 second pause between purge and wipe. It might help the filament to go brittle so that the wipe breaks it off more cleanly. TBH, I have similar problems with PET-G, even though I can travel and wipe, so that pause is something I plan to try myself. Apart from that, I guess a coated nozzle is about all that's left. Slice engineering have just announced a non stick "paint" that can be applied. That's something else I plan to try when I get the time.

    Edit. That said, most of my problems are because of oozing during printing because I haven't got the retraction sorted out with my experimental hot end.



  • Thanks, I will give the one second delay a go but I will let somebody else try the paint. Not even the specially coated nozzles seem to work all that well based on what I have read.
    Yes, there is oozing during printing but I got into this project because of dual material printing and the large amount of snot generated as the extruders change temperatures (from active to standby). The standard purge tower is totally overwhelmed and became pretty much useless. I have not yet tried to see how the wiping action deals with the material that is ejected from the PETG nozzle as it cools down to standby temperatures. It sounds nuts but that is exactly what is happening - a 4" or thereabouts extrusion from the 0.4 mm PETG nozzle as the Volcano hot block cools from 240 to 150C.
    There is also accumulation around the PETG nozzle (not at the actual tip) that will gradually collect until a big blob will drop onto the print making a mess of things. Currently it requires me babysitting the print (especially the first few layers) with a pair of tweazers at the ready to remove excess material from around the nozzle. I was hoping to eliminate some of that with a nozzle wipe every 5 or so layers but the wiping station is quite useless for that.
    I too will need to dial in my retraction settings but I am not too optimistic about being able to substantially eliminate the PETG stringing issue. I suspect it's the primary cause for the blob accumulation.

    Edit: When I manually remove PETG from around the nozzle, I can easily pull a wisp of material of two or three feet. This material is thinner then spiders silk and can take multiple seconds to float to the ground in still air. This (IMHO) is not something that can be eliminated by retraction. It doesn't make a difference if you have eliminated absolutely all drooling of the nozzle with retraction ... there will always be a bit of material at the tip of the nozzle that is enough for several feet of spider silk. Good thing is that a heat gun makes short work of the silk. Bad thing is that if the nozzle catches the wisk, it will add to the blob building around the nozzle.



  • @jens55 What you've highlighted is part of the reason why I ditched using multiple nozzles and went with the single nozzle mixing instead. But of course, multi materials is pretty much a no no (although I have managed PET-G and PLA but it isn't easy).

    When you finish with the PET-G nozzle, do you do a retract before you park it? I find that helps with oozing as it cools. But, yes bigger melt chambers = more oozing during warm up and cool down.

    Edit, so maybe std hot ends rather than volcanos. Have you experienced PLA hydrolysis yet? (Becoming more runny over time as it sits at print temperature). If not, you will. Again, the bigger to the melt volume, the bigger the problem.



  • Yes, I do a retract. I suspect that the action here is completely counter-intuitive. The retract pulls the material back a bit, it expands and blocks passage of material from the heat chamber. The heat chamber then cools and the material expands. Since it can't go up the heat break that is now closed off, it is forced out the nozzle.
    .... at least that is how I explain to myself what I see happening YMMV



  • @jens55 Who knows what really happens? I found I had a lot of oozing with the Diamond hot end as it warmed up at the start of a print. Always doing a retract at the end of a print definitely helps with that.



  • I have not experienced PLA hydrolysis (thank God!). I suspect it is because with two nozzles I am either actively printing or have dropped to a standby temperature (130 for PLA).
    I have only seen it (or something close to it) when I do a 'propane cleaning' of the nozzle.


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