January jumpstart!

'Allo folks, and welcome to 2024! Had a good holiday season, ey? Cover pic, view of part of my town that goes a bit nuts with the decorations.

I'm still on the whole 'clean up the day job'-journey and the store's paused, but so far so good on all of that. I'll spill the beans someday when I'm well past the 'all is sorted' threshold. Until then I'll simply say that things are going well, but even the 'good' scenario requires a lot of work.

Workshop stuff though! The holidays made themselves known by, among other things, causing a whole slew of slow deliveries for supplies. I ended up mixing the projects up a bit while waiting for deliveries, summary and thoughts below.

The rig:

• Pic1: walling up to cast a thicker edge ahead of prep for the 'top cover'.
• Pic2: testing surface treatments (because one critical vendor switched suppliers, boo) and the various release agents/barriers for epoxy. Also some ghetto-testing in case one of the iffy paints would work and save me a decent chunk of cash. No go, but was worth a shot.

The epoxy resin I'm using for the shell is proving a bit of a challenge. Holds up well, great mechanical properties and so on, but for the life of me I cannot seem to get any of the normal 'casting barriers' to work. 

Specifically, I've got the first "half" of the shell done, and need to cast the second (split) half on top of it. The edge that goes all around the mold is 'epoxy on epoxy' and needs a barrier between so as to not seal the whole shell together. Normally there's wax, silicone sprays, barrier films and such... but for whatever reason, none of them seem to be working in my tests. I'm not sure if it's the specific epoxy resin I'm using or what.

Test was simple enough - translucent resin in the bottom of a few plastic cups, barrier, then some colored resin on top. Wax, silicone barrier spray, film, misc paints, etc. Multiple layers of sealant/barrier/..., specific instructions followed to the letter for each method. No go. All stuck together like absolute units. 

I've still got a few outs for this though. First one is next on the try list - different epoxy composition from another vendor. If that works, we're fine. If not, I'll just do a full-on silicone gel barrier. No way the epoxy is getting through half a centimetre of solid silicone, and that'll also act as a nice seal for liquid-proofing the chamber later. I suspect this'll be the main thing over the next month.

Absolutely worst case I'll throw in the towel and just print the entire damn outer shell, but let's hope I don't have to do that :)

Holiday sidetask - resin printing:

• Pic3: resin printing going horribly wrong, and requiring 30-60min of cleanup before I can retry. Also another different slice where it came out alright...
• Pic4: ...but not alright enough. Dimensional/form accuracy is something I still need to solve. All those lines should be perfectly flush with eachother.

While waiting for some of the epoxy barrier supplies I caught up a bit with the resin printing. I'll frankly say that I can see why it's still niche, because jesus it's finicky in so many ways. I basically have three major issues that I'm slowly working on nailing down or otherwise getting past.

Before we dive into the issues, a quick recap for context. There are two main usecases I'm chasing for the resin printing - high-detail single-side latex mold prints (whether pos or neg), and detailed-and-accurate multi-part silicone molds. The key thing is the surface detailing and quality that you can't really get with FDM printing, which will both save time for existing usecases and enable new ones.

First, buildplate adhesion and even getting a print. On FDM printers it's easy - the more the item touches the buildplate, the more adhesion you have. Simple. On resin it's trickier, because you have two sides - the metal buildplate and the plastic bottom-of-the-vat. Depending on size of either, the positioning of the item, and even printing/retraction speeds, you may end up pulling the item off the buildplate instead of the vat-bottom. 

Trivial example - pyramid, 1x1cm on the buildplate, 5x5cm on the bottom vat. If you just yoink it straight upwards quickly, odds are good the small buildplate section will detach.

I've gotten a bit better at handling this by now, with angled items and careful speed choices. I might also be able to improve it overall by re-setting the plastic sheet in the vat bottom so it's ever so slightly looser. Looser plastic sheet, easier 'tear-away' of the item being printed. Takes hours to swap it though, so I'll save it for a necessary or desperate moment

Second, the dimensional accuracy. When you print something you'd like it to come out as CAD'ed. With FDM nowadays that's usually the case. With resin... Yeah, no, a lot trickier. When we talk about 'shrinking' during prints it's easy to get the mental image that the whole thing comes out smaller. That's not the case. Instead you end up with slightly deformed pieces - a straight line is slightly bent, an angle is bigger/smaller than it should be, etc. 

There's a reason you see a lot of e.g. wargame models or cosplay props printed with resin - the dimensional accuracy doesn't matter all that much for purely visual pieces. If the printed item is to be used for technical applications though... See pic. Besides the edge not being sealed, you obviously end up with interior faults and e.g. thicknesses not being correct in the cast.

In my case I've got two distinct usecases, one from each category. Single-sided latex molds are fine even if the dimensional accuracy is a little bit wonky. Half the reason I ended up doing them from the start, honestly. The double-sided molds, e.g. for silicone, is a different story though. If the pieces don't come out exactly as CADed the mold is basically useless. 

I've got a few more things to try with all of this. Most notably, upgrading to 'technical' resins with possibly better physical properties. Downside there is that they are a lot more difficult to work with from a chemical point of view, which brings us to point three below. 

Third, the toxicity. FDM is nice enough in that you're dealing with solid plastic, and can basically toss the waste in plastic/energy recycling. No major health annoyances when printing either, the heat/microparticles are miniscule enough that it's not noticeable. Resin, on the other hand... Toxic goop that in the best-case scenario is odor-free but still iffy. The more normal scenario is that it has a terrible eye-watering smell and needs serious ventilation for the room to even be survivable. Every print needs cleaning of the un-cured liquid, and that cleaned liquid resin isn't exactly flush-down-the-toilet-disposable. 

I've got a pretty decent ventilation system by now, and there's also the fume hood I built last year. Most of my experiments so far have been with the 'easier' resins, but I'm thinking of moving the printer into the fume hood soon and trying the 'difficult' ones to see how they perform. There are obviously people who have successfully printed technical parts, just gotta' figure out the tricks and get them all to click. Tech-resins will be an important step.

-----------------------------

Whew. Busy month, despite the big rig epoxy issue being a bit slow. I'll hopefully have solved it one way or another until the next post, and then we can finally hop onwards to having a complete'ish casting chamber. Genuinely psyched for this year, so many blockers getting cleaned up... and that'll let me focus on the workshop a lot more.

Keep your fingers crossed, ey? And as always, thank you all for the continued support! You know the drill, comments/DMs/... etc always welcome!

Until next round, take care folks!