@ElektroQuark For how long? Or, if not by time, how do you decide? By weight? By color? Or something else?
For about 5 hours. We made initial weigh loss test.
If you have the silica gel in the oven for more time the humidity lost is not really that big to be useful or practical.
Sometimes even 4 hours is OK.
You donāt need to have a completely dry silica but in an state that the water ab/adsortion is reactivated at full strength.
Is it really important the water capacity to be a 5%/10% more?
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I definitely agree on there being hazards with compressed air. Over the inside surface of that housing there will be many hundreds of pounds of force build up. If that housing canāt take it, itās almost a bomb. Just my opinion but I would find out for certain what pressure it is rated for before pressurizing it. High pressure stuff can get nasty and even a leak opening up can cut into skin and inflate a body. Itās pretty gruesome stuff but can happen. Had to see photos of that stuff when I took compressed gas training / Swagelok training years ago. Think water knife but with air. Compressed air can be safe with proper equipment and precautions, but using hardware in ways other than intended can present unexpected hazards thanks to the energy stored in compresses gasses.
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100% agree. I decided to delete the posts. No real loss, as they are probably of no interest to anyone anyway.
I wasnāt meaning for you to delete the posts. I just wanted to caution on the hazards. I cringed when I saw the guy in the video do it though. In a closed system, water under pressure loses that pressure fast if there is a leak, but with air, even with a leak it can be a hazard until it bleeds down low enough. But the safety stuff they showed us to impress how dangerous compressed gases can be were pretty brutal. One guy was over a big pressure plate that sealed up a railroad tank car sized tank and was just loosening nuts without checking if there was pressure. The bolts failed without warning and blew the plate right into him with massive force. Killed him instantly. And the images of people who inflated their hands (never check for a high pressure leak with your hands) were really gruesome. Those people needed big skin grafts if they didnāt just lose the hand. As an aside, we have a friend who used to work in power generation. They looked for steam leaks with a broom and would know they found it when all the bristles would get sliced off.
Obviously much higher pressures and way more dangerous conditions, but it shows how gnarly and even hidden the hazards can be. And then there are the guys at the Delta (IIRC) maintenance hanger that were killed and injured when the airplane tire blew recently. Compressed air can store a lot of energy in that pressure.
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Yes, and add to that all the unknowns that come from parts manufactured in China. Even if it says itās rated to a particular amount or standard, itās a bit of a gamble as to whether it really is or whether itās a swindle so that they can sell lesser or defective parts at a higher price.
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For a whole host of reasons, I think what Iāll do, and in retrospect should have done in the first place, is black box the specifics of my particular build. That way, assuming I get it working, we can still compare notes regarding effects of desiccated make-up air on the drying of filaments without it becoming a distraction. 
There are plenty of ways of making desiccated air, but long before the āhowā of it, most people are probably still wondering: why bother in the first place? When that case is made, and in many ways I think you already have, then I think more people will get interested.
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I havenāt made a standalone case except I get better and more consistent printing results with the dried spools. But like others have pointed out - how dry should it be? It only needs to be good enough to get the best prints.
But the air dryer can eventually get you to pretty low moisture content. I loaded spool #25 this afternoon and drying is slowing and the dark in the desiccant is over halfway up the reservoir now. All the water may be letting it now spread more on its own which fits - as the silica gets more saturated, it holds water weaker. Exit RH is still indicating 10%. Itās got to be getting close, though.
Anyway, if nobody is interested, thatās fine. Itās not a snap-together build and the parts arenāt cheap. And many donāt even have moisture issues. But for those that do, it might help. But if nobody builds it, thatās ok. You can plumb a similar system together with just a few parts, too. And honestly, you donāt need entrance and exit humidity measurement. By supplying dry air to a filament dryer it will dry to low humidity. Itās reliable enough to just watch the humidity in the filament dryer. The 10% floor Iām still not above makes exit humidity pretty worthless anyway. All thatās really needed is the pump, a container of desiccant, maybe some fittings, and some tubing which apparently comes with the pumps. What the real value is comes in knowing it works.
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Just took spool 25 off the dryer and have to stop again until the PETG gets here - just one unused cereal box left. Dryer still has output pegged at 10%. Visible discoloration in the column now about 2/3 up. I took this spool off overnight and that sets it back but taking a little longer than it did at first but not bad. Probably can do 30 spools. Column at end of spool 25ā¦
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Hey @NeverDie, just started test printing with the new spool of Bambu PETG-HF. Didnāt dry it - itās straight from the bag.
It was showing a little fine stringing and leaving little clumps on the build plate that were just there and not attached to anything. Iāll try flexing the parts to see how well they hold together. But I was hoping for more issues - the popping and sizzling some have mentioned, etc. Not a total meltdown but just bad behavior straight from the bag, but so far pretty well behaved except for the minor stuff which may not even be signs of water. Just running the stock PETG-HF settings and maybe thatās normal? At least I have something to see if it goes away.
Have you printed enough PETG-HF to say if that sounds like water?
I needed to test the output pressure I could hit with the new base that had been painted with superglue fresh off the build plate. Itās totally tight and can hit 9ā water column pressure with the pump throttle setting at minimum. Set at max thereās a really sturdy flow even at 9ā deep. I had to use a flower vase to get a container tall enough. Thereās no beads in it yet but for a pressure test they donāt really matter either way. But there is now ālotsā of flow if anyone wants that even though it will use up beads faster - though beads are easy to regenerate. Flow will go down some with beads in, though.
The plan is to finish this print and see about layer adhesion and any more stringing/clumps. Depending on if the current print has good strength (hoping it doesnāt), I may leave the spool just sitting out overnight after weighing it. I want some definite water effects so can weight it occasionally to see how much water itās picking up. Then tomorrow Iāll print again if these pieces printing now look too good. Once Iāve got definite water effects then Iāll start a dry in the new air dryer with fresh beads, record weights, and so on. Iāll know how much water it picked up if I do that and can then see how much it loses in the dryer.
I should remove what got added and maybe more if itās carrying much moisture straight from the bag. How the dry behaves will be interesting. I think any amount lost over what it picks up overnight if I need to leave it out will be an indication of how well it can dry fresh PETG-HF. The final test will be to print the same print and see if the issues go away since thatās really all we are after.
Almost there.
And the print is done. Came out pretty ok I think. You can see minor stringing (doesnāt matter for the application) and a little bit of adhesion on one part. Gently used smooth PEI with warm water and dish soap clean with fresh glue stick.
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I havenāt tried Bambuās PETG-HF yet. I previously had a lot of stringing with PETG, depending on the manufacturer, especially when I was using a 0.6mm nozzle. I do have quite a lot of PETG that I purchased prior to the pandemic still sealed in their original boxes. Iām all but certain that they are deeply water-logged by now. Iāve heard different opinions on whether that means it can no longer be rescued, even in theory. It shall be interesting to see whether I can rehabilitate it when I get the desiccated air working and hooked up to the dryer. If I can rescue those old filaments, the savings will help pay for the equipment.
I did some painting on a 3D print with Raptor today. As a result of that experience, I no longer recommend it for your project. It may be tough stuff when it finally dries, but it turns out the median dry time is a week, as opposed to just a day for 2K spraymax and less for some other 2K formulations. Also, you have to spray it from 3 feet away or it gets foamy, and that means that for the vast majority of 3D printed objects most of it misses the target. I hadnāt realized it would be so different from 2K spraymax.
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Were you going for air tight or just surface finish?
Waterproofing and added protection against UV for an outdoor object that will be under harsh direct sunlight.
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I charged the new air dryer version with fresh beads. The 3.6 pound Dry & Dry carton of silica gel beads will do two full charges of the 2 liter reservoir with about a quarter cup left over. The net weight in this new fill of beads is 804.98g. Itās actually a little overfilled.
I decided to risk āwetting upā the spool of PETG-HF so will be weighing it and setting it out to absorb moisture. Itās been in the AMS since I opened the bag with a humidity reading of 2. Will check it through the day to see how much water it picks up. Shooting for about 2g (WAG) to see if that makes the print go haywire.
I used matte latte brown for this build and matte desert tan for the old one so my pump lid (salvaged from the first version) is slightly off on color but hereās the two air dryers - one with the desiccant after 25 full spools were run through the dryer, and the new one now with fresh desiccant. The color change really stands out.
And not going to plan. In all the discussions of PETG-HF and water, I had thought it would just start soaking up water sitting out. Humidity is a little low right now compared to what weāve been seeing (about 40%) but still thatās significant. Itās not absorbing water - at least not with any speed. 2 hours in and the spool is weighing very slightly less than the first weights. I even removed and replaced the spool a few times to make sure I had a good reading but the scale was also moved between first and following weighings.
Iām going to give it to tomorrow to absorb water but that will be the end of that. Iāll print more clips tomorrow after weighing to see if any change but after that it goes in the dryer to see how that goes.
But at least the way it looks so far, letting spools of PETG-HF sit around exposed to room air for a while isnāt that bad. I havenāt tried this with PLA but I wonāt be in near the hurry I have been to get spools into containers or the AMS.
I didnāt quite follow: why are you wanting to make it worse? AFAIK, time tends to be a strong factor in moisture absorption for both PLA and PETG. Usually, a lot of time. Iād say maybe a week or a month. Not hours. Not that Iāve kept careful notes, but just going by overall impression from recollection. On the other hand, thatās how long it takes to become noticeable. I suppose it should pick up something measurable before then, so in that sense I suppose it could happen sooner.
Youāll know itās really bad when you can literally see bubbles in it as it extrudes. It also kinda contorts coming out the nozzle rather than go perfectly straight. Actually hearing it hiss and popā¦ thatās pretty rare, at least in my experience. Maybe extrusion temperature is a factor in that. You might try cranking the temp up if you want sound effects. That would maybe reduce the viscosity enough so you could hear it. Iām no expert on that though. Maybe others reading this might have comments in that regard. It would make for a convenient rapid moisture test: does it hiss and pop? If so, off to the filament dryer!
I was naive on the water absorption rate for the filament. I had just heard so many say how much it likes to absorb water that I thought it would a bit more rapid of a process. But the intent was to get it to misbehave while printing and see if I could dry it back out. It was trying to approximate the issues some people see. But since the rate is so slow, Iām just going to stick it in the dryer tomorrow and see how it goes.
ā¦ and it went well. Total water loss was 3.38g drying to 21% RH in the Sunlu chamber and a print using it (the same print that was stringing just a very little and had a small amount of corner lift with filament fresh from the bag) came out perfect. No stringing at all and no lifting. Not an exhaustive test by any means, but they recommend drying before use and before/after showed definite improvement. YMMV.
And itās up. For better or worse. If anyone is interested in this and has any problems, donāt hesitate to ask.
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Send a link in to Hackaday. If they pick it up, which they really should, that will help spread the word. 
It feels a bit like the end of the Fallout series, where they finally get the cold fusion working and they can light up the world.
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Except Hank went bounding awayā¦ 
I donāt know how many problems it will actually solve, and again, people can duplicate it with just a container of silica gel beads, a straw to make the air travel through the beads, an aquarium pump, and tubing.
With fresh beads it will work as long as you seal it up. It may not be the ideal shape (a column/cylinder), but should be good enough to see the effect. Thereās a big difference in drying with dry air and ambient humidity air.
Building the model I posted is a fair investment in time and money but just plumbing the pump to desiccant to dryer and getting it pretty air tight is all anyone needs to do to test it for themselves.
About spreading the word, Iād like to make sure others see real improvements. My own water problems are really pretty minor. Iām in a low humidity area most times of the year. The differences Iāve seen seem real to me but have thankfully not been too bad. Certainly not like some of the images that get posted. What I do know is I see pretty consistent drying and with full spools have been around 2g weight differences.
But anyone thinking about it might want to try just rigging up a setup first.