Hi all,
I’m getting into printing rock climbing holds for a home climbing wall and want to explore stronger filaments than PETG-HF.
PAHT-CF seems promising but the drying requirements are quite high.
Would something like this:
Work well to dry the filament?
Ideally looking for a dryer that would work well for this and PETG-HF. And a food dehydrator seems like a good option.
I bought a different food dehydrator but it only went up to about 55C.
Thanks,
Boaz
Why not something like this? 
Obviously I am joking but there are so many posts here where folks show the “blast furnace” they want to use to dry filament, but it’s completely unnecessary and so totally over the top. Even Bambu’s own recommendation is you can dry filament right on the heat bed, it just takes longer so the notion of hotter is better is not necessarily a “must have” but more of a “Want to have”. Sure, an oven that goes to 11 rather than 10 might seam really beefy and one would have bragging rights and maybe it even speed things up, but spending $120 on a massive oven for drying is way overkill, considering the fact that the device becomes a brick just wasting space. This device takes up as much room as an A1.
But don’t take my word. If you’re amazon Prime member then buy both the oven and a purpose built dryer. You got 30 days no questions asked for full return on their dime. Then do a literal “Bake-off” between the two methods and return the one that doesn’t measure up and then you have something really juicy to share here with the community.
I did this with the Creality Pi and the Sunlu S2 which I posted a review here. Sunlu S2 VS Creality Space PI Bake-Off Review Amazon never questioned the return.
Thanks for the detailed response and suggestion!
I will definitely consider what you said!
Maybe a comparison between the Polydry and the one I mentioned! (Polydry has a discount right now)
There are a lot of threads about this topic I just haven’t found anything super definitive saying hey just use 70 C it’s fine. It just may take longer.
But what you’re saying makes sense.
Yeah, I feel your pain. There are a lot of opinions① but few who verify with actual facts and data they have personally verified. That’s why it’s always recommended that you do your homework, which you’re clearly doing, and then go validate the answers with your own experiences and test data. There is no substitute for your own personally gathered empirical data.
A few things to keep in mind about filament drying - ambient humidity sets a floor for moisture content. When drying, if drying on the build plate, get a hygrometer to stick in the chamber with the filament. Filament dryers have them built in.
The reason you need a hygrometer is that floor set by ambient humidity. There are curves characteristic of materials that relate humidity and moisture content. If you “dry” a spool in a chamber with high humidity, water weight loss will be reduced and just weight alone won’t explain why you might have a low weight loss. The humidity will - or it can provide confidence you got a good dry.
You’ll get the best drying if you heat the filament in a dry air environment. It works great. Food dehydrators are designed to exchange a lot of air with the outside world and so are unsuitable for use with dry air but work great if you are in a low humidity environment. If you are in a high humidity environment then a food dehydrator might not be the best choice.
That makes sense! My house is always right around 50% humidity so I’m not sure where that places me, I’ll do some research. I have a decent size grow tent that I’ve been using to hold my SV08, it may be worth tossing a dehydrator in there as well.
With 50% humidity you won’t be able to dry filament to as low of moisture content with a dehydrator. Might be fine with PLA since many have pretty good luck at higher moisture content, but the more hygroscopic stuff might get difficult. Can’t really say in advance. Also, some effects will only show up over time depending how you store filament as it absorbs water.
If you are using desiccant, you need to monitor humidity and keep humidity low. It depends on desiccant type, but for many water binding is totally reversible and water can come and go depending on environment - including putting dry spools in with “wet” desiccant which only hydrates the filament. Also, dry desiccant with wet filament will slowly remove water from the filament but it’s a very slow process. It’s not practical as a drying method. But dry desiccant with dry filament is a way to keep filament dry for long periods.
Good stuff! The polydryer has been ordered as well as a thermocouple to test a dehydrator I have to see how hot it gets! Hopefully this will be enough to get stuff dry!
Sounds good! If you ever want to dive into the empirical data I used to reach my conclusions, it’s in this thread (https://forum.bambulab.com/t/filament-drying-preliminary-results) but has some detours and other topics in it. But it’s all there. Also various humidity/moisture graphs and such are there that explain why I focus more on humidity now and less on weight loss.
There were a few of us brainstorming and testing this stuff but there is data backing up everything I said here.
I have a Sunlu S4, which I use to dry PAHT-CF and everything else. The temperatures in the S4 are not quite as high, but PAHT-CF still dries in a maximum of 24 hours. The dryer runs alongside and that’s it.
I’m the guy who always suggests the Graef DA 2042 food dehydrator. 
(Think it has s different name in the US). Though admitted I don’t have one yet nor a dedicated filament dryer due to insufficient space for either.
Just a few questions and thoughts about the statements in earlier posts.
How do the dedicated filament dryers help against humid environment? Do they somehow actively dry the air other then by temperature? Or don’t they exchange the air as well with the environment to get rid of the extracted humidity? the Sunlu S1 and S2 and others even need the lid to be not fully closed so the humidity is not trapped. If there is no extra magic, then the food dehydrator should even have an advantage due to higher temperature, which causes the relative humidity to drop further.
Just in case you aren’t aware: the capacity of air to hold water rises with temperature. So if you heat up air, the relative humidity drops. If your environment has 25°C and 50% RH, the absolute water content is 10g/kg . If you heat that air to 50°C, it only has 12,8% RH, at 70°C it is at 5% and at 80°C it is at 3,3%.
The cheap hygrometers used in filament dryers typically don’t go below 10% where it would get interesting. They are notoriously inaccurate. I bought a pack of 10 and the measurements were all over the place with 18% between lowest and highest reading in the same place.
I don’t know if for engineering materials like PA, the 70°C of filament dryers are really enough. That applies especially to PA because it is so very hygroscopic. I’m not convinced that leaving it longer in the dryer can compensate that, but maybe that works. Would be interesting to see a real comparison.
The only analytical comparison of filament dryers and food dehydrators I’m aware of is by CNC Kitchen. He didn’t find any difference between dedicated and food dryers at the same temperature. And he used one of those very basic plastic dehydrators. So the better food dehydrators going higher in temperature should have an edge.
The only downside I can see is not being able to directly print from them. For me that doesn’t matter because of the AMS. The Graef is cheaper, more powerful, better isolated, has higher max temp, higher build quality. So technically, for me the decision would be absolutely clear if I had the space. As I don’t, drying on the print bed seems a very good solution, because of the higher temperatures compared to a dedicated dryer.
Did you see my post two days ago about the 150C-capable dryer I built? Check it out here.
The standard filament dryers don’t do anything about humidity and just use temperature to lower the humidity and help with evaporation - but ambient humidity limits how dry a standard filament dryer can go. It basically imposes a floor on drying.
Food dehydrators exchange a lot of air but are similarly limited by ambient humidity.
Filament dryers and food dehydrators work fine for many when ambient humidity is low but this past summer there was a flood of posts about print issues due to moisture when humidity was up for many.
If you want magic for drying filament, the best I’ve found is to use a small pump to flow air through a desiccant column and feed that dry air into a filament dryer. The air coming out of a desiccant column can be very low. I’m hitting 2% RH air according to a cheap hygrometer I use with a half-spent charge of silica gel where I’m probably seeing some breakthrough. Some desiccants should pull humidity to fractions of a percent.
Feed dry air into a filament dryer and it can purge moist air out of the dryer and the reduced humidity speeds up getting moisture out of the filament. You can dry to lower moisture content faster.
About your other points, it makes sense they saw no difference between food dehydrators and filament dryers at the same temperature since both are limited by ambient humidity. Using higher temperatures to get adequate drying can move into the area where filament sags a little and takes a set on the spool but obviously depends on how hot you go.
Food dehydrators are designed to exchange a lot of air and aren’t amenable to modifications to purge them with dry air. You actually go the other direction and want the filament dryer semi-tight with air escape holes at the top (since humid air rises).
About the cheap hygrometers and numbers being inaccurate, I was surprised by how tight the cheap hygrometers I’ve been using were in the numbers they gave. Virtually identical with none out by more than a single percentage point. At least with the ones I’ve been using the difference has been getting a bit of air into the ports on the hygrometer.
With still air they are fairly slow to respond, but direct an air flow into the port and they get much faster and respond with nearly identical or identical measurements. Obviously there could be other differences but this was the big thing I found. It may just be sampling error. Many or most of the sensors are factory calibrated and respond nearly identically with a flow of air.
You could also dump a bunch of hygrometers into a poly cereal box, seal it up, and give it a few hours to overnight to equilibrate on their own. They should all move to the same or nearly the same numbers as the sensors all equilibrate with the air in the poly box.
Using desiccant to blow dry air into the dryer is super interesting! I wonder how feasible a poly dryer mod for that would be.
Do you have any data on how much it helps?
That’s super cool! Skimming through the article I didn’t see a total cost, what did that run you?
It seems like a super cool build. I want to get into load cells in the future.
heh, thanks! it didn’t cost much because i had most of the materials on hand. filament cost was my biggest hit, since i was using premium materials. if you went with polycarbonate for the whole thing, you could handle that with a $30 1jg spool of Polymaker PolyLite PC. following that, a PCB with SMT elements would likely cut the electrics bill in half (i’m literally working on a PCB now, breaking away from KiCad to reply). you could also get away with a much cheaper motor (the one i used is $15, and totally not worth that price). i think you could do it for less than $100 even with PAHT-CF.
No idea on a Polydryer mod. I’m not familiar with those. But for how much it helps, there’s a long thread about it with some other stuff. https://forum.bambulab.com/t/filament-drying-preliminary-results
It helps a lot. I was also having moisture issues this past summer and that’s what led to my involvement in this. I’ll put some before/after photos.
It still takes a while and there’s diminishing returns like anything. Even though you can dry to arbitrarily low moisture content, going really low still takes time. It’s because at lower humidity in the filament dryer the slow step becomes water finding its way out of the filament.
There’s another user here who built their own dry air supply and they related that they weren’t able to get below 28% RH in their Sunlu filament dryer. With a dry air purge they hit 16% RH in their dryer in 11 hours if I am remembering correctly.
Here’s PETG HF used for some netting clips. I printed straight from the shipping bag and got doughy surfaces and some lifting from the build plate. After drying the clips were perfect:
Here’s PLA before and after drying:
Not everyone needs dry air for filament drying. A lot depends on your humidity and even how and what you print. But if you are having moisture issues and regular dryers aren’t fixing it, dry air might be the sauce it takes to fix things.
Good stuff! I’ll have to look into it if this polydryer doesn’t solve it for me!
That’s awesome! I’ll definitely have to look out for that pcb!
Do you have a YouTube channel or anything where I could follow this project?
sorry, not nearly so organized nor audience-oriented =]. your best option would be the “recent changes” link on my wiki, or watching my github, which i certainly don’t expect you to do. if i get the PCB and BOM where i want them, i’ll probably sell the PCB along with a sack of parts, and would in that case post it to reddit and maybe here, or anywhere else relevant that won’t ban me for spam heh,
