Spool from PETG HF deformed by drying another spool of PETG HF?

Bambu Filament and Accesories Filament
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Hello,

I am a little (pretty) confused and would like to hear your opinions. I have a spool printed from Bambu PETG HF (Orange) and I just took it out of the dryer where it had been for about 8-10 hours at a temperature of 65°C (another Bambu PETG filament was drying on it). To my surprise, the spool is deformed, and quite badly.

What I find strange is that I have more spools printed from PETG and I usually dry them at 65°C for xy hours. And so far, I haven’t encountered any problems. In fact, it never occurred to me that any could arise. The spool was printed recently and, as far as I can remember, this was its first drying.

The other printed spools I have are models from Andythilo - Voronoi versions, which have thicker side walls. I have about 5 of them, and they are printed from both Bambu PETG HF and Devil Design PETG. There were no problems with them (I have now checked them all) … they have gone through several drying cycles at 65°C. This problematic model (also from Andythilo) is Hexa-Honeycomb and is more subtle - it does not have such thick walls as the Voronoi version. I have two of these spools - both printed a few days ago from Bambu PETGHF Orange … the second one is fine, but it has PLA Basic on it, so it only went through lower temperatures.

I admit that I am quite confused and don’t really know what to do with it - what information to take from it. This spool is obviously ruined - the only thing I can think of is respooling, but my point is that I’m starting to doubt whether PETG can be dried on a PETG spool at the recommended temperatures (65°C) ??? I’ve been doing this and it never occurred to me to doubt it. And if it doesn’t work, how come it worked for me until now? Is it possible that the properties of PETG differ depending on the color? And that they differ so much? Or something is just wrong with this particular spool of filament?

Technical note – it also occurred to me that I might have mixed up the materials when printing the spool (that it wasn’t PETG), but I ruled out that possibility. I have three versions of the orange color here – one of them is PLA, but the shade is different. Another is PETG from Devil Design, which also has a significantly different color. This color comes 100% from Bambu PETG HF Orange. Moreover, I only print spools from PETG, and the print profile only contains this material – if I accidentally put PLA instead of PETG into AMS, it will fail during printing.

I would really like to hear your opinions or experiences…

TW

PETG Ruined spool
PETG Ruined spool1920×1442 151 KB

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Additional information – the dryer is a Creality Space PiX4, and I don’t think there was a problem with the drying process. The temperature was set to 65°C, and there was another spool (also printed – Voronoi from blue PETG) alongside the damaged one, which is fine. The filament itself on the destroyed spool also seems to be OK (so the temperature inside the dryer probably did not exceed the set temperature).

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It may have been set to 65°C but what was the actual temperature? I’ve taken to putting my own trusted photo thermometer in my dryer to keep an eye on things, and the temps at times are all over the place.

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Good tip. However, even if the dryer is/was the source of the problem— heating more/higher than it is set to and showing on the display … how is it possible that one printed spool of blue PETG is fine, but another of the same material - just a different color (orange) - is ruined? Both were there during drying… same time, same conditions - whatever was going on there.

This is bothering me. Anyway, tomorrow I will try to find a wireless Bluetooth thermometer what I use for cooking (Meater) and take some measurements… will see what’s going on there

BTW, thanks for your response. :+1:

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Many dryers have a very uneven temperature distribution, e.g. temperature close to the heating element could be significantly higher than somewhere else inside. Maybe that could cause it?

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I had a bambu spool, which are good for up to 70c, warp a bit in Sovol SH02 set to 65c for drying. I stuck a thermometer in the back and found out the air coming out is around 80c until the dryer chamber reaches 65c. So I no longer use that for PLA and PETG.
This might or might not be your issue as well, most dryers have hot spots. I only use ams 2 for drying PLA and PETG now, no issues with the same type of spool. I think Eibos has one that rotates the spool too, probably that one would be also good.

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Quick, someone say “hysteresis”!

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So, part of the “mystery” seems to be solved, but some questions remain:

1 - Why did this happen (temperature in the dryer) – yesterday I took my Meater Bluetooth thermometer (I use it for cooking and grilling – to be honest, I have no illusions about its accuracy, but it provides basic information and I don’t have anything better) and put it in the dryer. For those who don’t know, the Creality PiX4 has two compartments, each for two spools. I set the temperature for drying PETG (65°C - which, by the way, is also the predefined temperature for drying this material) and first placed the thermometer between the spools. Everything seemed to be perfectly OK… the display showed 65°C, and the thermometer showed 63-64°C. Great.

But then I moved it to the back, above the openings through which air from the heating element enters (or assume that). I expected the temperature to be higher here, but I was in for a surprise. The temperature changed depending on the “heating cycles”… it easily rose above 70C (which I would have expected), but after a while it reached almost 80C before it started to drop again! And it definitely wasn’t a matter of seconds… yes, it’s just one spot, but even so, the temperature difference is quite large. I then moved the thermometer to the front, where there are more openings, and the temperature jumps were similarly large. I didn’t have much time to continue testing in more detail, but I still think it answers (or it could answer) the question of WHY it happened… but some questions remain…

2 - Why didn’t this happen earlier? As I already wrote, I have been drying this way for quite some time (two months, to be precise) and nothing has happened so far. Unless we consider that the dryer recently “broke down” and started heating more than before, then I don’t really understand why the deformation didn’t occur earlier. I dried both the original Bambu (gray) coils and my own, printed from PETG – I use two versions (both from Andythilo) – Voronoi and Honeycomb.

3 - Why did one spool survive and the other not? At the time, there were two spools in the dryer - both printed and both made of PETG HF (Bambu) material. One blue in the Voronoi version, the other orange in the Honeycomb version. The spools are similar, only differing in the thickness of their sides - while Voronoi is quite “massive”, Honeycomb has… let’s say… normal dimensions. Is it possible that the larger amount of material handled the temperature better?

Or is the reason in the different properties of the filament - that its color affects it? That blue (for some reason) is more resistant than orange? It seems very strange to me, but I’m still considering it. Does anyone have any experience with this? I have read that there are differences, e.g., in the strength of the material, but would this have such a dramatic effect?

Or is it possible that this particular piece of PTEG orange filament is simply defective and does not have the properties it should have? However, I believe this would have been apparent during printing, and that went completely smoothly ??

–
By the way, for now I decided to reduce the drying temperature by at least 5°C to create some reserve for those temperature jumps/differences. And I am considering making some kind of “temperature” shield for the dryer that would deflect the hot air from the vents so that it does not go directly to the coil, but to be honest, I don’t know if it’s possible or if it would work at all …

I am quite interested in your opinions…

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BTW, for those who are interested, I don’t have to invent anything. After a quick search on MW, I found some solutions… so obviously I’m not the first one to encounter this problem. Let’s try it and see if it works… :slight_smile:

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It seems like the root problem is in the way your dryer regulates the temperature. Either it is damaged or it employs a simple hystersis regulation like: temp drops 10°C below target temp → turn heating on; temp exceeds target temp by 10°C → turn heating off. For drying, you obviously want a very constant temperature.

I would guess that the thicker rim has saved the voronoi spool. but well possible that different colors behave different too.

I have to post here a short rant about those filament dryers:

It is really hilarious how the manufacturers of dedicated filament dryers fail to identify the most important properties for successfully drying filament and applying them, while the basically same devices for other purposes fullfil them for many years.
The first point they all missed apparently is, that the air has to be exchanged so that the moisture can escape. A homogeneous, constant temperature is another obvious property that seems to be rocket science.

I currently use our air fryer for drying filament. It does everything right, keeping temperature within ±1…2 %C and steadily blowing the air out at the back. It also achieves any temperature between 30 and 230°C and probably it is more energy efficient because it is well isolated.

My wife is not that happy about that double use, so I think about an AMS HT instead. But I really have to think about it twice and if I buy it, the first thing will be measuring the temperature at several locations.

Food dehydrators also seem to still work much better than dedicated filament dryers.

It’s really hard to understand.

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Food dehydrators generally have way bigger fans than the filament hotboxes, and is a reason I like em. It makes me feel like I’m stirring the air enough to actually getting the air exchanged out of the inner wrapped windings so that I dont have to dry this damn spool twice. I’m probably not, but yknow.

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