I've always wanted a skateboard that is fast and easy to use that I can easily bring on an airplane without any hassles. I've also found, when showing up for business meetings, that clients and collaborators often look at me a little funny when I'm dressed somewhat formally and I have a briefcase in one hand and a skateboard in the other. On top of that, I've never really liked the standard "longboard aesthetic" to begin with.

The top deck:

In it’s folded state:

In it's closed state, the board is meant to look a bit like a vintage briefcase. The handle is designed in such a way that it is flush when in "rolling" mode

The final design is a fair bit different from my original design. The overall shape is about the same, but it’s more narrow and the hinge is upgraded.

I wanted the folding mechanism to feel very smooth, so I chose to use shoulder bolts with teflon washers. The two hinge pieces on one side are in frictional contact with the head of the bolt and the edge of the shoulder respectively. The threads go into the “inside” hinge piece. This configuration ensures that as the hinge opens and closes that the bolt is turing with both pieces and thus there is no relative motion between the head of the bolt, the threads and these two pieces. They all move in unison. In contrast, the other two pieces are in contact with the shoulder of the bolt and the teflon washers. This prevents the thread from loosening (although I should probably use lactate anyways).

It’s hard to see clearly, but the handle is recessed into the wood support block in such a way that when the board closes into “case mode”, the handle is no longer visible.

Since the composite structure of the board is made with burlap, epoxy and wood it’s really hard to get a good feel for the yield strength and modulus of the material. I took some guesses and did FEA anyways using SolidWorks Simulation. These results are really only good for confirming (or contradicting) my intuition. The absolute numbers here are meaningless.

From certain angles you can see how the walls would flex. The flexure here is exaggerated to help with visualization.

I assumed the load was in the center of the board.

I wish I chose to do a concave mould rather than a plug. The plug was easy to mill on the showboat (out of two thick pieces of HDPE “King Starboard” marine grade plastic. That said, as you’ll see in the following photos, the process was a pain and there were lots of defects.

I bent the wood by using the plug while the wood was wet. As it turned out, this process was unnecessary. I later had to remake one of the pieces because the epoxy did not cure properly (I poured the last little bit of a the cup in at the end and I must have grabbed the wrong cup with unmixed epoxy in it! rookie mistake). Anyways, when I remade the piece the second time, I simply hot glued the wood into a bent shape and then did the layup. The epoxy took care of the rest.

Regardless of how time consuming it was, there was something kind of satisfying about bending wood by using water and letting it dry.

Here are all the parts for the layup of the inside layer.

Burlap is a huge pain to work with. It’s never flat. I tried holding it in place with cyanoacrylate but that was more trouble than it was worth. As it turned out, temporary hot glue did the trick. I had to scrape it off later with a blade.

Moulding moldy mould mould… I did so many layups I went a bit loopy after a while. I’d strongly recommend getting some good gloves, and setting up your area so that you do not stress your back. If you’re tall like me, almost all tables are too low for this kind of work.

The vacuum bag works ok with these kinds of parts, but as you can see there are regions of poor pressure where the bag can’t “crush in” because the vacuum bag is stretched to it’s limit (not it’s elastic limit, but to the point where the vacuum is insufficient to stretch the material any further). This happens on round edges the most. AS it turned out, this is also where I had wrinkles and a few unbounded areas. To avoid this, you can pull in extra material and massage it into place while the pump is on.

The inside layup came out nicely. It helped that there was little or no overlap in the burlap and thus no sharp bends that would lead to delaminations and wrinkles.

Shows the handle bracket in progress. The pecies are much longer than they need to be so that it was more simple to make the “support block”. I had to maximize the area of the bond between the block and the “deck”.

I water jet cut pretty much all of the metal components. The handle was cut from 0.667” aluminum and the hinge components from 0.23”.

CNCing the block of wood on the showboat was a huge pain. The slots for the hinge parts was exactly 0.25” wide and the bit was the same thickness. As a result, the path (using PartWorks3D) would not go into the slot like it should. I had to enlarge the width so that it would work. It was a guess and check process because I could not figure out how bit the “gap” had to be in order for the path to go where it should. I also tried doing it in 2D using PartWorks, but this had problems too. The path was shy of the boundary of the wood by about 5 or 6mm. I could not eliminate this problem so I just stuck with PartWorks3D with wider cuts.

The hinges were not as snug as I wanted them to be, but it turned out to not matter at all because I ended up manually milling holes into them so that I could fasten them. Originally I was going to epoxy them in place, but fasteners enabled me to make sure they were positioned perfectly in the x direction (along the length of the board). In addition to providing some redundant strength, the ledge on the semi circular part of the part was supposed to help with locking down the x-position, but the dimensions were off a by about 0.06”. I ended up using shims which doubled as a load distributor so that the hinge would not crush the wood when in tension.

The outer layup was hell. I had lots of overlap (a design choice) but the burlap would not behave. Hot glue was going to help this time because it was the final layup and I would not have the opportunity to cut it out after. In this case, I just had to have faith that the vacuum bag would do it’s job and everything would get crushed together with minimal wrinkles. As it turned out, most of the wrinkles were due to the places where the vacuum bag could not stretch any further. I was amazed how the overlaps worked out given how hard they were to set into place when spreading the epoxy.

Peeling the epoxy, gauze and release layer off of the part was a pain, but it would have been even harder had I chosen to wait another day. Because I did it before the epoxy had fully cured, it was more flexible and this helped a lot. It was still hard to do though and in the future I might try to find a way to break up the release layers so that it’s not a monolith of fuzzy garbage.

The part turned out fairly nice, but had a few wrinkles.

I did a fitting of the blocks and hinges and I ended up having to sand them a bit so they fit into the deck.

Epoxying the blocks into place was fairly easy and I fixed a few delaminations while I was at it. Small c-clamps would have been better. I used a release layer on them knowing that the epoxy would squeeze out. Rule of thumb: put release layers down even if you think you won’t need them.

Once I screwed in the tiny fasteners everything synched up and felt super smooth. It’s basically done here but it requires some filler epoxy, some finishing some painting and some final clear coats.