Resin finishing

I have some filament,

I have some resin.


Filament resin!

Today I’ll try to combine some of the advantages from filament printing, that is cheap, fast and can do large prints with the surface finish of actual SLA resin. Let’s try it out! 

Just a quick note, we’re working with resin today, make sure you’re also wearing gloves and appropriate safety gear. I mean, not when you’re watching this video, but if you decide to try this out for yourself.

Before I even started with the actual experiment, I did a quick test to see whether it was actually worth making a whole video on resin finishing and oh boy, did this have promise. There were two small issues with this trial where I just literally dunked the part into the resin VAT on the SL1, and that’s that there is this massive elephant foot from where the resin piled up on the bottom of my container, and obviously this is neither pretty nor practical, but if you look at the branch structure in here, many of the branches have also fused into a big blob.

I think that’s because the resin itself is actually quite thick and has a fairly high surface tension, so it likes to round out inside edges. I did give it quick spray of grey primer, just to show the actual surface of the part, and the actual effect I was looking for, that is hiding the layer lines, that’s actually working out really well.

So to get started on the first part, what I did was to thread a pair of screws into the bolt holes on the part and then I stuck it onto the container using a pair of small magnets, so now we have a gap where hopefully the resin can just drip off and not leave that big foot anymore. On that first trial, I just had way too much resin on the part that I then had to get off somehow. So this time, I brushed on some resin, tried to get it into all the nooks and crannies, but because this was still quite a layer that I had just put on, I then used a hot air reflow station, which is basically a precise, adjustable heat gun, and just lightly heated up and basically blew off as much of the resin as I could.

When resin is warm, it gets a lot more liquid and all the small bubbles that the brush left also instantly pop. The problem is that the lowest this station goes is 100°C, so if I left that on my part for too long, it would just melt so I had to be pretty fast with moving it across. Once I was happy with that coat, I tried to get as much of the resin to drip off and I chucked it into the CW1 to harden the coat. That’s the nice thing with this UV resin, you can work it as long as you want, it doesn’t “dry” by itself, but once you’re happy with how it looks, you just pop it under UV light and it hardens pretty quickly.

As it turns out, the heated resin actually gets pretty liquid and leaves layer lines fairly well visible, so I added two more coats on top and always popped it back into the CW1 for a cure cycle between coats. What I’m definitely still seeing is that we’re losing quite a few details, some of these branches are starting to disappear and inside corners are getting rounded out a lot.

With the hot air reflow station, it’s heating up the already thin layers at the surface pretty quickly, but the pools on inside corners and the areas around details have more mass and more of the base part contacting it, so they’re taking longer to heat up and become liquid. So open surfaces had most of the resin running off, but in the inside corners it still accumulated quite a lot.

When I went to clean up that first part, I accidentally dripped some isopropanol into my resin container and that gave me the idea to actually thin down the resin before applying it. With just a thin layer of diluted resin, the solvent should evaporate off fairly quickly, and if not, I can always help it along with the “drying” feature in the CW1 or some warm air, but the extra runniness at the start should be enough to get it out of inside corners quickly – plus, we have the exact inverse of what we saw with heat. Because inside corners have less surface area and more mass in the resin pool, the solvent should actually evaporate more slowly in corners and keep the resin runny for longer. I started out with a mix of roughly 2 parts of resin and one part solvent, and this immediately made the resin a lot thinner. I mean, as expected. In fact, I could straight up pour the mix over my part and all I had to do was to make sure it got into all the creases and I could then have it drip off into my container.

A few more coats and cure cycles here, too, and actually, I do really like how this turned out. It’s covering up all the layer lines, but still retains a lot of details. Also, this was so much easier to apply – just pour it over or brush it on as thick as you want and you can then just let the excess drip off. And the surface finish is actually better than when I was using just pure resin, if you look closely, you can see some wrinkles in here, but I think these come from not having an underlying layer of resin fully, totally cured yet before applying the next one.

And since the thinned down resin worked so well, why not keep going? This time, I mixed up more of a 1 to 1 or 2 to 1 mix – that is two parts solvent, one part resin. This stuff is suuuper runny, definitely much closer to pure isopropanol than to resin, and I did the same thing – pour it over, drip it off, cure it. It’s weird, because the surface almost instantly turned super smooth and glossy on the first coat, even though this mix is a lot thinner now. One more thing we can see with the super thinned down resin is that the areas where there was more resin pooled up turned cloudy white. That’s probably because I didn’t let the IPA evaporate enough before hitting it with UV light to cure it.

My favorite one of these three is the mildly thinned down one, but I did enjoy how easy it was to apply the super thinned down one. It’s really about time – if you use thinned down resin, you need to factor in the drying time between coats, on top of the curing time itself. If you’re finishing several parts at the same time and coat one while the other one is drying and curing, that’s totally fine, but if it’s just one part it makes for quite a bit of awkward standing around, because obviously you’re wearing contaminated gloves and probably don’t want to take them off and throw them out between coats, but it’s still a bit too long to just stand there and wait for the curing to finish. Still, it’s a lot quicker than either spraying and sanding a finish or mixing up a 2 part resin, applying it, and waiting for it to cure.

These parts actually worked out incredibly well. All three versions have their ups and downs depending on how you do it. But, since this worked out so well, I wanted to try something a bit bigger. This is an alien egg that I printed on the Raptor 2.0 using the E3D super volcano with really thick layers, and you can definitely still see them. There are also holes in this surface because I didn’t have the settings all tuned in and with a nozzle that big and a layer height that tall it’s not going to be perfect. So let’s try if we can finish this part with resin and make it waterproof, because this is supposed to be a planting pot. And obviously it doesn’t fit in the CW1 any more. So to harden resin outside of a curing station you can either use a little UV flashlight like that but that just takes forever to do because it doesn’t have a lot of power or you can do what I did: I grabbed myself one of these driverless 50 Watt LED chips and these are incredibly bright. But if you run these make sure you have a case around them because there´s open main voltage on this PCB.

And because this thing is so incredibly bright you should also put on some eye protection.

I’m using Wanhao resin for this one, because I’m thinking I’ll need quite a bit of it and this Wanhao stuff actually doesn’t harden properly when I use it in a printer, so why not use it up in experiments like this. This is supposed to be yellow resin, but I think the pigments have settled into a crust at the bottom of the container, so the resin looks more like, i don’t know, liquid snot or something. But the consistency is pretty much perfect for this alien egg, I want this to look slimy and wet and disgusting, and a thick layer of resin is absolutely going to help with that. So, lets glob some of this stuff on.

I started with the top, petals, I guess, those still had some holes in them from the print, and the resin covered most of them instantly. A quick flash of UV light and…. what? What’s that smoke?

Well, turns out if you harden the resin too quickly it actually overheats and cooks itself, and it looks like it also detached from the print a bit. But it did harden almost instantly! This means I can go right ahead and apply the next layer of resin. I went ahead and did about two coats on the entire thing, some areas got a bit more, some a bit less, it’s just hard to cover everything evenly in basically clear resin, but if you look at how this thing turned out – wow. The surface is really smooth, and with the thicker, high-gloss resin on it, it really does look like it’s covered in slime. Which, actually, it was. The Wanhao resin still didn’t cure properly, so it was left with an oily layer on top – either that’s totally uncured resin or it’s some component of the resin accumulating on the surface, either way it’s not great, so I gave the entire thing a wash in IPA, which took off most of the sticky layer – at least enough to apply the final surface finish on top.

That’s going to be a gloss coat. I thought about giving it an opaque coat first, but that would lose that depth of the resin layer and just give it a flat, even color. So just the clearcoat, let’s do that right now and then let’s compare my results to what it would look like if I just used the resin as intended, and, you know, just printed the parts directly from resin.

So that’s what that looks like. Obviously the resin print still has a lot more detail, I printed this one at 0.035mm layer height, that took a while to finish, but it doesn’t quit have the same glossy surface. I guess you could still spraypaint the resin print and get that, but unless you have a crazy massive resin printer, you’re not going to get something this size.

These brackets are normally over 3 times the size, and I think at that scale, losing a bit of detail isn’t much of a problem at all, unless you’ve got a part that does some mechanical job, but while resin coating you can always mask off surfaces that need to mate with other parts.

I definitely like this resin coating approach a lot and I think this is finally a good and quick way to get rid of print layers. I’ve experimented with nitrous filler, spray filler, 2 component bog, and a bunch of other approaches, but this one is by far the least effort, and in comparison isn’t even that messy. And if you still want to do more, unlike PLA cured resin actually sands pretty well.

Looking for a quick and cheap way to remove layer lines from filament prints? Try using some resin from your other, SLA printer! It’s an alternative to using filler and sandpaper, XTC-3D or other ways of adding a second skin to your prints – but it can be hardened in seconds with UV light!

Alien egg by crazymany2099

50W UV Leds

Orange resin is Prusa’s “Tough” resin

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