So! The Beast Ball is nearing its final form, but it still has a few issues with it. If I just wanted to stop at a multicolor version, I would have finished a long time ago. However, that would alienate a lot of users (and results in a lot of purging waste!), so I really wanted to make a single extruder version with each piece printable separately.
I figured it would be interesting to talk about what exactly goes into making a model like this, and why it can be tricky to get it perfect on the first try, just off the top of my head:
In essence, it all comes down to the fact that 3D printing is just a little bit... squishy.
When a toolhead extrudes filament, that plastic doesn't end up occupying the exact space that the 3D model did on your computer; it squishes out ever so slightly like a tube of toothpaste left and right, which makes parts just a tiiiiny bit bigger than you might want.
As a result of this, if you take a model made for AMS, hit “Split to Objects,” and print each color out separately, you'll find that you simply won't be able to fit any “peg” pieces into any “hole” pieces. The amount of squishing involved is very, very small, but given that happens 4 times (two pieces + the fact that it happens on both sides of the connection) AND that your margin for error is quite literally 0 means that the pieces just won't fit together.
Frustratingly, while shrinking the pieces down in your slicer might work in some cases, it definitely doesn't work in all.
For example, what if you have a piece that both fits into something and has something else fitted into it? In that case, you need to increase the size of any holes, and decrease the size of any tabs, which really isn't feasible to do in-slicer.
So, we have to intentionally model them in from the start, and make an entirely separate version for that purpose. Which, I know, isn't great, but that's the way the cookie crumbles sometimes!
Now, you may think that it's as simple as using an “Offset Face” tool or somesuch in your CAD program of choice to shift the faces over a bit (by the way, I found that only moving one of the model's faces over by 0.05 mm gives a really tight fit, and 0.075 gives a more smooth one), and you're mostly right, but there are still some things to think about:
Corners. 3D printers' round, squishy nozzles aren't great at making round corners, so when making pegs, it can be a good idea to round off their corners for an easier fit.
Support. If a hole involves support interface, it can result in a rougher surface, which requires even more tolerance in order to get things to fit.
Overhangs. Similar to support, if something overhings a bit too much, it might not be as smooth of a surface, and might need a bit more clearance.
Elephant's foot. This refers to the phenomenon of the first few layers of a print getting squished out, if the print head is a bit too close to the bed. Since it squishes in all directions, it might impact the print's ability to fit together if any of the joints are affected.
To give a more concrete example, this top piece just doesn't fit on properly. Why? A couple reasons.
Namely, I removed the fillet from the pegs because it was glitching and causing an error, and there were support interface structures inside the holes the pegs fit into. This resulted in a rough fit, and I couldn't even press it down all the way. I most likely will need to open up the holes involved a bit more, or more likely, just completely redo the connectors to not require supports.
Now as for the best way to do that, well… I fear that I've rambled on long enough, and I have an idea for a separate, full explanation of that topic in the pipeline. Lemme know if you're interested in that, and don't forget to follow!
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