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Fighting with Nylon ;) Answered

As some might know I still use an old Gen1 Prusa but love the challenge of basically getting everything done with that oldie.
One of my latest challenges of "always" printing on a cold bed includes Nylon.
If you ever had troubles because you ABS or PLA filament got too moist you will already know what happens to your print...
Nylon is even worse when it comes to moisture as you can't see or really feel it.

I was thinking of making a complete Nylon guide as an Instructable but think I will start here to kick off some discussion first.

So, we know the Nylon must be really dry for a god print as otherwise we get bubbles, bad adhesion and of course a foamy looking print.
Well, not really...
Let me explain:
A perfectly smooth and shiny finnish is not always required, and with the right settings Nylon still forms strong bonds even with a foamy look.
However, the dimensions of parts are affected as well - outside dimensions go bigger and hole diameters smaller.
If that is no issue for your print then there is no real need to perfectly dry your filament ;)
Speaking of drying:
People use all sorts of methods to dry their filament, not just Nylon.
One of the most common and most expensive seems to be the use of your oven for several hours to dry it.
Another way involves food dyhydrators, bit less on the energy bill but still...
Then we have the smart guys using the sun and silaca gel for the drying - good and great but so useless in cold and wet climates...
My advise here: Take your time!
I mean, sure you want to print right after the filament arrived in your letter box but a bit of preperation will save you filament and frustration.
Usually filament comes in a sealed bag with a pack of silica gel and it should be dry and ready to use.
But Nylon can become too moist within the time it takes to finnish a long print if you are in a wet climate.
This means you start printing and all is good but the next day your new print looks ugly as for no real reason.
Make use of these sealed storage containers.
Put the filament in there with a good amount of indicating silica gel and only have a hole to feed the filament through - if in doubt use a bowden fitting and a short lenght of teflon tube to prevent friction.
A piece of sticky tape over the hole when you don't use the filament and the filament is always ready to use.
Reminds me to make an Ible for a suitable storage solution with spool holder...

Anyway...
When it finally comes to print Nylon you should know cardboard works best as a bed as Nylon sticks really well to it.
I glue mine onto a layer of masking tape, this way it won't lift from the bed and I can still replace it very easy.
But the most common mistake with Nylon is to print it too fast.
The stuff really expands and shrinks a lot from filament to print and high speeds only too often cause the layers to seperate later on.
Some people compensate with higher temperatures but I don't like the idea of fitting a filter system with activated carbon filters...
Also keep in mind the intense shrinkage when setting the extrusion multiplier!
If your ABS prints fine with 0.85 you can expect that the same sized Nylon prints fine somewhere in the range of 55-60!
Now you also know why printing with thick layers is not such a great idea if you require all dimensions to fit.
Although only outside accuracy can be done by cheating in the settings, getting outside, inside and extrusion widths settings accurate is almost rocket sience ;)

Nylon is expensive or not available here in the diameter I require....
I had the same trouble and reverted to trimmer line and a modified, dedicated hotend instead.
Why dedicated you wonder?
Nylon can be real pain to clean as nothing dissolves and if you heat the parts hot enough to melt it you can not work easy with them.
Having a decicated hotend means you won't run into the problem of burnt ABS or PLA clogging the nozzle ;)
It also means you can match the hotend to the trimmer line you choice (more on that in a minute).
For example, in some areas trimmer line of 2mm or 3.3mm diameter is the most popular and cheapest.
Just drill out the hotend to cater for the new diameter, which I did after noticing the filament got stuck in the neck of the cold end ;)
Trimmer line - does it matter which one?
It does these days!
Avoid everything that is not round or labeled with terms like "duracore", "dual core", "multi layer"  -basically all that indicates it is not just a single, solid stand of Nylon.
Long lasting, special core line is great for your lawn trimmer but really bad for your hotend!
PET, High temp nylon or even fibre re-inforced cores are in use, so in the best case you mix the nylon with overheating PET, in the worst you block your nozzle permanently.
If it looks like it has a core or some sort of "mantle" around it, it means not usable.

Discussions

I'm not famaliar what kind of setup you have but I'm thinking maybe you could make an enclosure around your spool and just have a hole in it where you could stick either a hair dryer in it or a heat gun. I would go with the hair dryer so you dont have the priblem of overheating and melting anything . this would work great at keeping spools dry that have already been dried. Not suggesting doing this instead of drying.

Nice one, thanks!
I did not know about them but as you can see it is 60$ for 450g of Nylon filament :(
That is why I went the cheap way with trimmer line.
Currently printing other things in PLA but will take some pics of the finnished nylon parts tomorrow, time permitting.
Trimmer line in 3mm goes for around 50$ on Ebay - for around 1kg...
You just have to pick the ones without a core or extra outer layer.