In terms of Vision Miner’s secondary advice, of using dry nitrogen or argon, I’m almost doing that, but presently with just normal desiccated air to keep the filament dry inside the drybox by supplying just a slight positive pressure:
I’m using an an oxygen flowmeter to dial the pressure all the way down to just above zero. I’ve been running it 247 for two days straight, and only just a little orange desiccant turned green, so extrapolating from that, I figure I can get about 10-14 days out of it before the ambient air burns through.
As you can see, I have extra desiccant in the drybox as a kind of backup and maybe a little extra scrubbing. After burning through an entire column on a previous trial though, it remained orange with no green.
If I need to do a purge on the drybox, as when first setting it up, I can turn up the flow all the way to 4-5lpm. I like having that kind of flexibility.
The purpose of this particular setup is to keep TPU dry while printing. That’s why there’s no bowden tube on the path coming out of the drybox. This is a harder scenario than when you have a completely closed path from drybox to printhead, which is the more normal case with other filaments.
I’m also using a wireless TH sensor inside the drybox to monitor the dryness of the air inside.
This is just something I lashed together. For a more polished setup, look into what MZip has published on makerworld:
By the way, as with MZips design, mine is powered by an aquarium air pump, so there are no significant pressures involved. Many thanks to @MZip in proving that such a pump is sufficient. IIRC, it may max out at around 4-8psi. I had earlier built one utilizing an air brush compressor, but that turned out to be the wrong approach for a whole host of reasons I won’t go into here.
As you can see, the total cost is quite low, and the benefit is guaranteed dry filament for the duration of your print. If you’re printing an expensive engineering filament, the cost is practically a rounding error in the grand scheme of things.
In a future version, I may take it a step further by inserting a stage or two of even better drying desiccants to further mop up after the first pass by the silica gel. That would take the air even closer to the Nitrogen or Argon dryness that Vision Miner is recommending in the screenshot above. That’s partly why I built this using quick-connects: it will make adding additional stages as simple as snapping them in place when that time comes.
Anyway, the point isn’t the detail of my particular build. The idea is easy enough, and there are probably many clever ways to do this. I still think @MZip’s design is the best place to start for anyone considering this.