Calamity with a microswiss nozzle.

Discussion in 'Volcano' started by sevenoverthree, Jun 7, 2018.

  1. sevenoverthree

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    I have been enjoying the volcano setup on my CR-10 5S for about a month now. I have a few projects that I want to print foodsafe, so I picked up a stainless 0.4 nozzle by microswiss and started printing some test items with some Hatchbox PETG which I keep in a drybox. All systems were go, so I embarked on the first more serious print, which ended up running about 16 hours.

    By the end of the print, I a little PETG oozing out of the top of the heater block. When I tried to unscrew the nozzle, it was clear that PETG had crept its way into the threading. Not good. I started by heating the nozzle to around 90c and started pulling the bigger gobs of PETG from the aluminum block. Most of it pulled off pretty cleanly at that temp, but it was not enough to get the nozzle and heat brake off. I increased the temp to about 120c and managed to pull the nozzle and heat brake free. The microswiss had a thin layer of PETG all the way down the threading, however on the heat brake, it appeared to be clean where it meets the nozzle- let's call that the bottom. The bigger surprise is that the "top" of the heat brake- where it comes out of the heat block also had some PETG. I am not sure what to make of this, because there should be PETG running all the way up...

    Here's a link to an album

    In the process of removing the heat brake, My pliers slipped, and I roughed up the threads, so I think that's the end of that heat brake. It won't smoothly thread back into the upper heat sink, so I ordered a replacement, and will probably just bin the heat brake.

    The heat block has a little bit of PETG inside where the heat brake meets the nozzle. I am considering hitting it with a butane torch and maybe getting a Q-Tip with alcohol to try and swab that little bit out. If I fail, I did order a replacement heater block :(

    As to the microswiss. The threading is all fine, but it's horribly coated in PETG. I would love to save it if I can. There seems to be little to no solvent based fixes here, so I am not sure if there are any clever ways to get this threading properly cleaned.

    Bear in mind I had made a real effort to seat the nozzle properly. I had printed for a few weeks with the 0.6 brass nozzle, and it worked beautifully. The nozzle switch was a complete non issue. The brass came out clean as a whistle. The stainless went in perfectly, but clearly something happened during the longer print.

    So as you read and look at the photos could you all please weigh in on what might have gone wrong here? I essentially had to replace half of the E3D setup, and may be purchasing a new stainless nozzle. The $60 or so I spend this one time kind of sucks, but I really would rather not end up in this situation again. What can I do better? Is it possible there was maybe a bit of a flaw in the microswiss nozzle? Perhaps I should have tightened the heat brake into the heat block a little more? Any feedback would really be appreciated.
     
  2. Antoine

    Antoine Well-Known Member
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    Have you hot tightened the nozzle? This looks like the kind of failure we see in non hot tightened hotends. https://e3d-online.dozuki.com/Guide/V6+Assembly/6?lang=en#s89
    We can't guarantee the quality of the Microswiss product. Our nozzles are toleranced to fit our blocks well, it might be that the thread used on the Microswiss nozzle is of a different tolerance.
    The nozzle being stainless steel, it is even more important to hot tighten it. The coefficient of expansion is higher in aluminium than in stainless steel, so as your block expands when it heats up, a gap appears between the top of the nozzle and the bottom of the break inside the block.
     
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  3. orcinus

    orcinus Well-Known Member

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    I know this doesn’t help at all, but it’s a warning i keep giving out, whenever i see this...

    FDM prints are *inherently* not foodsafe because of their geometry!
    No matter what nozzle you use, no matter which material you use, no matter how clean your hotend and extruder - an FDM print cannot be considered or called food safe.

    The gaps between the layers are a nightmare from a bacteriological PoV.
    You might call it food safe the very first use. That’s it. And that’s if you can guarantee no residue from your extruder, no residue from your hotend, no residue from your PTFE tube throughwhich hundreds of other filaments went through, no residue in the material stock itself etc.

    Don’t call it ”food safe”.
     
  4. sevenoverthree

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    Thank you for the input- I definitely did hot tighten it at 265c, but I didn't go too hard because I was worried the stainless of the nozzle would be strong enough to potentially strip the aluminum heater block. Perhaps I should have let it stay at temp for a little while longer? I believe it was at temp for maybe 30 seconds. Thinking about the thread tolerances a little more, I will probably purchase the coated E3D 0.4 nozzle next. Any suggestions of how I might be able to save the Microswiss?

    And when I try this again, do you think it would be good practice to hot tighten it every few prints? I am happy to be diligent, but I also don't want to strain the aluminum block. There's nothing worse than the feeling of tightening into something made of aluminum, then that instant give that tells you you went too far! :)
     
  5. sevenoverthree

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    These parts were a project for a friend, but sounds like we should talk through the use case a little more. Maybe we can find a way to make it work. You bring up very good points.

    I think the pressing concern initially was the lead composition in the brass nozzle leaching into the plastic, but it's true those layers are definitely prone to be problematic. Technically having everything exposed to 240-250c should kill all the bacteria passing through the nozzle, no? Also, the parts are pretty thin, so we could feasibly go 100% infill? Perhaps we could also anneal them after the print?

    In any case- I appreciate your comments on this. I think my friend and I were a little quick to assume the application would be fine. We will definitely do some thinking on this before we give it another go.
     
  6. orcinus

    orcinus Well-Known Member

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    Yes, but bacteria are not the only problem - you simply can’t control the whole chain. There might be non-biological contaminants in other parts. There could be oils, grease, metal flakes.

    Some form of annealing might work for the layers, yeah.
    Alternatively, it might be an option to seal/coat the print with a food-safe epoxy.

    In that case, you don’t have to even care what you’re printing the object with.
     
  7. Antoine

    Antoine Well-Known Member
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    You should only need to hot tighten it once. We have not had any cases of nozzles becoming loose over time. You don't need to tighten it too much, the guys here in our assembly line tighten them to 2N/m, so really not that much. turn it until you start to feel like you're tight up against something.
     
  8. ov_darkness

    ov_darkness Member

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    There are many ways to make your prints "safe"
    You can autoclave them, sterilize with radiation and chemicals.
    Of course coating, or using material that will be bacteriostatic by design (either releasing ions of silver/copper, or some other biocide, like formaldehyde).
    PETG is not foodsafe, as almost all grades (except of T-glase) release quite a lot of glycol (substrate manufacturers allow for some unpolymerized glycol to remain in pellets).
    We've even tested some medical grade PETG (it"s more PCTG as it contains CHDM) and qlycol bleeding was minute, but still present.
    I'd prefer to use PA, or SLA resin. My customers achieved some good results with DWS Systems Therma 289.
     

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