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mesheldrake

Surfboard - BoardCAD Thruster

by mesheldrake May 17, 2014
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Hello.
Would not it be better to use a simulation program?
As the AMSYS for example, to test the wear with different materials?

Gets the hint

Yep. (I think you mean ANSYS.) That's a fun approach too. Love those trippy FEA rainbow visualizations - especially when they're free.

The CAELinux distribution includes open source computer aided engineering tools, including some FEA tools. http://CAELinux.com

There are people taking that approach to surfboard engineering. Probably more with sailboard and wakeboard engineering.

Think I'm more interested here in the practical issues of printing. This is not a quest to engineer an optimal perfoming structure for an aquatic sliding aparatus. Yeah, I'm thinking of a variable density bone-like structure, but in the context of slicer software fill strategies. Interested in different materials for their behavior while printing large objects, not as much for their structural and dynamic performance later, at this point.

Maybe I should frame the project like this: what kind of surfboard will a RepRap-class 3D printer make today? Expected answer: suboptimal! But let's see what it takes, for real.

I think its better to print the honeycomb vertically , then just fiberglass. I prefer a single winged swallow thruster or twin about 6.2 feet and 2.5 thinkness :)

Yeah, but then the deck or board bottom is facing the build plate, so you get into printing support structures for those contours and the rocker - simplified a bit if you cut the parts into top and bottom slices. hmm. Then your deck and bottom countours come to depend on the lower Z resolution, rather than XY. So the skin layer would have to be a bit thicker to leave room to sand those smooth. hmm.

While I'm not planning to print and assemble this particular model, I do print and assemble large models so I'll share how I do it successfully. Keep in mind that I'm using PLA, so your properties will vary.
For bonding, I mostly use West System products. I've found G-Flex epoxy to be the best way to bond PLA, but 105/206 works fine as well. I've also used 105/207 when I've wanted a clear, but it needs a larger overlap for the glue joint as it doesn't bond quite as well. I sand with 60/80 grit and wipe with acetone. I've bonded ABS together with epoxy as well (though not 3D printed parts) and found it easier to bond than PLA (though I use isopropyl alcohol instead of acetone for obvious reasons on ABS). Oh, I usually add some colloidal silica (406) to the epoxy to keep it from running, since it doesn't soak into the plastic like it does to stuff like wood and thus, tends to drip more easily.
For making parts line up correctly, I either create the parts with registration keys so they fit together (you have to make sure your printer is calibrated for whatever your clearances are or be prepared to do some sanding/filing to get a good fit) or print jigs for the parts to hold them in the exact position while the epoxy cures. I always sand the bonded model smooth after assembly to get rid of the joints. Oh, and I clamp them while bonding.
When using jigs, or making molds from an assembled part, I put on several coats of paste wax and spray with release agent (I've had good luck with Mann Ease Release 200). Since I'm using PLA, parts/jigs pop off pretty easily after the epoxy cures.
I'm not a surfer, so you'll have to take this part with a grain of salt, but personally, if I were going to print a surfboard, I would assemble the board and use it to make a fiberglass mold. I would then use the mold to make regular (I assume) fiberglass boards. The other option would be to print and assemble parts of a female mold and skip the fiberglass mold step. For many applications, I print a positive and use it to make a mold because I find it gives me a better parting line than printing a mold directly (and it's much easier to sand smooth for a good surface finish), but I wouldn't think that would be an issue in this case since you'd probably go over the final board with fairing compound, etc. Anyhow, the advantage is that it's a lot faster to wet out some fiberglass in a mold than it is to print and assemble a huge part, so you'll be able to bang out boards and still get the benefits of a CAD-styled shape.
Additionally, I tend to avoid plated sets of parts because if something does go wrong, you're out way more time and material. I usually print individual parts. Yes it does take more time and planning -- some of my parts take me weeks to print -- but results in less overall waste. I've also taken the time to get my printer really well calibrated and have the process down to where I get no curling, etc. It really really helps if you can print nearly perfect parts.
Well, hopefully you can get something useful outta that core dump. ;)
If you have any questions, please ask.

Why the hell would you use epoxy? Look, epoxy is hella strong but 3d printing materials generally (as they are plastic) have a better bonding method. You want to fuse them into one solid piece, not glue them. Get a solvent and do it the right way. It will be stronger in the end. (epoxy is strong but doesnt compare to the actual surface bonding strength as fusion does. Epoxy also breaks down in the sun after a few years, it occurs a haze and can become brittle and crack. (you may notice this on some types of pebble walkways) And being that this is a surf board, in this case epoxy is even worse. Pla is said to be biodegradable and that it breaks down under UV radiation, and this is true, but the time scale for this compared to epoxy is drastically longer. Plastic can take 100's to 1000's of years to break down, regardless if its organic or synthesized.

We do fiberglass laminations on surfboards with epoxy made for that purpose. Boats are made with epoxy. There are definitely different formulations with different performance characteristics, some probably not so great in the sun, others meant to be in the sun for decades.

Totally agree with your point about epoxy being inferior here to plastic bonding with plastic. ABS is easy - just use acetone. But grozny's PLA process would probably need Tetrahydrofuran, which sounds like it's harder to get, and a bit more dangerous.

I keep thinking I should give solvents a try. What solvent(s) have you used for bonding PLA? I've already got a whole setup for working with epoxy, so it was a natural first choice. It also fills small gaps, which is nice. I've never tried to use these parts as the actual parts mind you, only as an intermediate step between CAD and the actual part. The properties of PLA pretty much exclude it from pretty much any practical use I would have for it other than a model or casting plug.

Also, it would be cool to see one of your large object productions illustrated somewhere - maybe a thingiverse thing that's more about the process than the actual thing, or an instructible or something. You could push people's imaginations beyond their print envelope.

Thanks for the tips.
Mold making is certainly the way to go for large objects like this in a production context, and 3D printing the molds probably is not the best way to make them, right? (I've got the CNC router for that.)
PLA is probably the way to go at first.
I'll update the description to address some of the other points you mentioned.