The part I'm not confident in is getting the hot dry desiccant converted to cold dry packaged desiccant, without degrading it.

Posted by: @cwbullet

Thanks.  I will keep an eye out for a small convection oven at Goodwill or on sale at Walmart.  

I spread them out on a baking sheet and set my oven to air fryer mode at 200° (400F) for 2 hrs. 

Posted by: @hyiger

 

Posted by: @cwbullet

One desicant question: Can you microwave Alumina desiccant?  I see conflicting info on the internet.  

Alumina is used in microwave windows and as substrate inside microwave equipment. So it's safe.  However, I've read (somewhere) that it's not very tolerant of thermal shock, if it goes through a fast temperature swing it could crack. I generally just pop it in the convection oven and allow it to preheat. It's non-toxic. 

Posted by: @cwbullet

One desicant question: Can you microwave Alumina desiccant?  I see conflicting info on the internet.  

Alumina is used in microwave windows and as substrate inside microwave equipment. So it's safe.  However, I've read (somewhere) that it's not very tolerant of thermal shock, if it goes through a fast temperature swing it could crack. I generally just pop it in the convection oven and allow it to preheat. It's non-toxic. 

Posted by: @conrad-2

IMO, bottom line is we can get a general idea of the humidity below 10%, but not with any great accuracy/certainty. Still, should be plenty good enough for any 3D printing.

Unless it's PA6 or PPA, generally < 15% is good enough in my experience. And anything cut with CF goes in the drier regardless before a print. 

I think it's probably the best consumer grade sensor available and the datasheet shows the typical and maximum tolerance limits. I wish it were a bit better but I also wish for world peace. Placed in a bag of freshly dried (600+ F kiln) 4A molecular sieve, which should be down at 1% or less, it reads about 6%.

My Creality SpacePi X4 supposedly uses- https://eleparts.co.kr/data/goods_attach/202306/good-pdf-12751003-1.pdf

I've seen it read 11%, but the sensor is located in a different place than the filament and it doesn't agree closely with a Switchbot placed in the middle of a filament spool. The Switchbot is also limited to a maximum of 60 C.

IMO, bottom line is we can get a general idea of the humidity below 10%, but not with any great accuracy/certainty. Still, should be plenty good enough for any 3D printing.

Posted by: @conrad-2

As a metrology geek, I tend to trust nothing! I have various humidity measuring devices that all agree closely, including a chilled mirror device of my own design, but there are many pitfalls when you get to the signal digit numbers. 5% is a dewpoint of about -9 degrees F and I don't know if my chilled mirror can get down that low. What I can say is that as things dry out, the response seems to be linear, so I doubt the readings are way off. Fortunately, we're not so interested in the high humidity end. We have to subject our products to that where I work and the humidity sensors we use don't have a great lifetime under high temp and high humidity conditions. I'm still of the opinion that keeping a large amount of filament dry with a small amount of silica gel is a big ask.

Good points about readings.  I just purchased some sensors that make a promise of accuracy and I still need to test them.  I created a chart to calculate RH% based on the dew point to judge what I need to think about and when I should be concerned.

As for meters, I have experienced the issue of a so called good meter to find that between 5 of of them, I found over 10% RH difference when all were placed in the same bin.  Useless.  At least the ones I am using were within 2% under the same test, they don't read below 10%RH.  Of course, for 99% of our usage, 10% RH at 22 degrees is more than dry enough.

Silica is not that efficient for moisture absorption so I agree that it would be a challenge.  One reason I moved to activated alumina.

Posted by: @crab

When you live in a temperate maritime climate, you quickly realize how much moisture affects filament, even PLA. I”m constantly drying desiccant in a microwave while also occasionally redrying both PLA and PETG in my PrintDryer. I’ve gotten several of the Polymaker dryer units which are more convenient, but I find my PrintDryer works better. 

The one thing I’m more concerned with, and no one addresses, is cardboard spools. Eventually filament will absorb moisture, but I’d think the cardboard spools would absorb it at least as fast. Once this happens, if you just dry the desiccant, you’ll be drying the cardboard more than the filament. I only buy plastic, reusable spools now. Since Prusa is 3x the price in Canada, my go to filament right now is from Bambu because of cost and spools.

The one thing I’m more concerned with, and no one addresses, is cardboard spools. Eventually filament will absorb moisture, but I’d think the cardboard spools would absorb it at least as fast. Once this happens, if you just dry the desiccant, you’ll be drying the cardboard more than the filament. I only buy plastic, reusable spools now. Since Prusa is 3x the price in Canada, my go to filament right now is from Bambu because of cost and spools.