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I have one 3D printer with Makerbot mk10 extruder and I would like to print my custom cup for tea or coffee from PC.

Other than that, I came across idea that FDM printer will always leave small holes on a surface, so they will be a perfect place for bacteria and make them hard to clean for dishwasher.

As far as I know, we have several techniques of polishing, like acetone vapor bath for ABS, however, I haven’t heard about something like that for PC and not sure if it's food-safe.

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I also print coffee mugs. I have used ABS for a long time, and, given the statements here and elsewhere about bacterial growth sites, have been attaching my life to a thread. That's fine for me, but I don't make mugs for anyone else.

There are three areas of concern I've found so far:

  1. The plastic may be toxic,
  2. The machine itself, especially the nozzle, my deposit bits of lead (Pb) into the object, and
  3. The small gaps may harbor pathogenic bacteria.

The toxicity of the plastic can be addressed by researching the FDA website. ABS is generally safe, although additives could be questionable. Also, for some reason the FDA lists ABS as safe, but not for use with alcohol -- so much for beer steins. Since the actual MSDS for hobbyist filaments can be hard to get, I'm considering using a less controversial plastic. PETG isn't good enough -- it softens at the temperature of boiling water (I know, I've tried). My next attempt at non-ABS will be Poly Carbonate. I have a spool queued up, but it is as yet untried.

The nozzle can be replaced with a stainless steel nozzle, which does not contain lead. Perhaps because they aren't heated, no one seems concerned about brass feed gears in the extruder.

The layer gaps might be addressable by acetone smoothing. I haven't had great results smoothing mugs. The first problem is that after smoothing a lot of acetone remains in the ABS. Even after a couple of weeks, when hot water is poured into the mug the acetone in the plastic vaporizes and creates bubbles in the surface, which completely defeats the purpose. I've also seen more long-term age-related cracking in vapor-treated ABS. This could also be due to gradually losing acetone and the surface shrinking. If one were to use acetone smoothing, I would suggest post-conditioning the mug in a heated, partial vacuum chamber to encourage the acetone to escape.

The method I intend to try to seal the inside of the cup is to use a food-grade two-part epoxy. I haven't done it yet, so I don't know how it will work.

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  • $\begingroup$ Good point about acetone. And for polycarbonate, it looks like we have only even more toxic solvents, so I think it's not an option as well. However, maybe something simple like sandblasting or something else could work could work apart from epoxy? According to articles I was reading about food-safe resin they're safe only up to 50C or 120F, so it looks like we can't use it for tea or coffee, unless they're cold. $\endgroup$ – Stepan Novikov Nov 4 '19 at 20:25
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    $\begingroup$ From the FDA information I found, polycarbonate looked good for food safety. $\endgroup$ – cmm Nov 5 '19 at 0:44
  • $\begingroup$ I've been thinking 3d printing will create a market for a new food-safe resin sealer product able to resist higher temps (dishwasher drying cycle) where perhaps one didn't exist or wasn't large enough before. Perhaps something like a clear brush-on enamel. You'd still want ABS and steel nozzle (don't mess around with lead), but it's something to watch for. $\endgroup$ – Joel Coehoorn Nov 5 '19 at 16:41
  • $\begingroup$ As for the brass gears... it's not the gears staying cool that makes them okay. It's the filament. A molten (liquid) filament can, like most liquids, act as solvent; it's more ready to absorb or dissolve other material into itself. Since the filament is still solid while moving through the gears, any transfer is much less likely. $\endgroup$ – Joel Coehoorn Nov 5 '19 at 16:45
  • $\begingroup$ I would like to try such a sealer. The 2-part epoxy kind is inconvenient to use. A solvent-based material would be great. And, thanks for proposing the plastic-as-solvent mechanism for transferring brass contaminates to the plastic. Has anyone analyzed the E3D nozzles for lead contamination? Lead is not an essential component of brass. $\endgroup$ – cmm Nov 5 '19 at 18:04

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