Spool Mount for Thermometer/Hygrometer Display, Fully Parametric.

If you want to seal up a spool of filament with a hygrometer display in a vacuum bag, where do you put the display? At first I thought of mounting it in the spindle hole, but my filament spools all have solid tubes for the spindle hole so that's effectively a sealed compartment separate from the filament when you suck the air out of the bag, so that's no good. Anywhere else and it's a fiddle to make it sit where you want it. 

So I designed this simple mount which can be adapted to any rectangular display and any spool width and edge thickness just by changing the fully labelled FX Parameters in the Fusion360 F3D file.

I've included the STL and 3MF for my particular spools (Elegoo PLA+) and the Thermometer/Hygrometer units I bought ( https://www.amazon.co.uk/dp/B07DHRRZHF ) so if you happen to have that combination then you can use the STL or 3MF, otherwise it's probably not going to fit and you'll need the F3D :o)

Once I started using hygrometers, which was today in fact, hehehe, I immediately learnt how utterly ineffective are those piddly little sachets of desiccant you get with the vacuum bag kits or even the bigger ones that come packed in the original bag with your new filament. I mounted a display on a reel of PLA+ which has always been kept vac-bagged with a little desiccant sachet between uses, and it read 45% when I vacuumed it and it was still reading 45% when I looked at it 8 hours later and the temperature was about the same. So that means the desiccant (I did use a new one from a sealed bag) has done absolutely nothing to reduce the humidity in the tiny amount of air left in the vacbag! I also packed another display in a vacbag with a new sachet and nothing else, no filament, and so no more than a tablespoonful of air around the sachet and display and the rest of the bag was flat - again no change at all in 8 hours, 45% and same temperature the whole time. I did the same test with a display and one of those dehumidifier containers you put in airing cupboards etc to suck out the moisture, and within a couple of hours it was down to 20%. 

So basically if you're going to leave a spool in a vacbag for months without opening it, then you might get away with a sachet in there, but if like me you're opening the bag every few days and using some of that colour and then rebagging it, the chances are that during that storage time the humidity level in the bag is exactly the same as the humidity in your room, and the whole tiresome exercise is a complete waste of time!

For PLA therefore the eSun vacbag system seems only of any value for long term storage. For TPU and other highly hygroscopic filaments I'm going to be building a drybox with a properly large amount of desiccant in it, and that will be opened once to put the spool in, and left in there including during printing (Bowden tube to guide it out of the box) until either the desiccant is exhausted (which shouldn't happen if the box is never opened) or the spool is empty. This mount isn't meant for that application because you can't take any filament while the mount is in place, but for anyone wanting to monitor a spool in storage this is a handy way to get the display in a place where you can see it through the vacbag.

I'm aware that these little hygrometers are far from calibrated, but they can tell the difference between 20% and 50% relative humidity and that's what I'm interested in :o)