I’m about to embark upon my electric skateboard build. This question is about construction of the deck. Here’s my plan. I’m going to use multiple layers of 1/8" Baltic Birch plywood with multiple layers of carbon fiber between those layers (so the outer surfaces will be plywood with inner layers of carbon fiber, so n layers of plywood with n-1 layers of carbon fiber).
Each section of carbon fiber will have a layer of 6K tow running parallel to the board (which should add significantly to stiffness), and two layers of 5.7 oz cloth placed at 45-degree angles to the board for torsional rigidity.
There will be a thin layer of Purpleheart veneer on both outside surfaces.
I’ll use epoxy to bind everything together and will vacuum bag it all to get a high quality, low epoxy content board.
The board will be approximately 42" x 9".
Here’s my question for anyone with carbon fiber experience (I could guess). Should I use 3 or 4 layers of the 1/8" Baltic Birch plywood. If 3 will give me a stiff board, that’s what I want. If I have to, I’ll go with 4. I haven’t worked with carbon fiber before and so don’t know how many layers I should make the board. I just know it’s renown for its stiffness, especially the UNI.
I haven’t used carbon fiber but I did make my own board so I can give a little input on the wood part.
My board-
44" x 10"
5 layers of 1/8" maple (I think) plywood
Alternating grain going length wise for 3 layers and grain going width wise for 2 layers
Just used wood glue and lots of clamps, no vacuum bag
Pretty stiff
I’ve been riding it for about a year now and I don’t know if I’m getting fat or it’s getting more flexible but it’s starting to have some more flex to it. When I first made it, then almost no flex even if I jumped on it (I’m about ~170lbs). Now I can feel some flex when I step onto it, but not enough to make for a soft ride.
My friend’s board I made-
40" x 8"
3 layers of 1/8" maple (I think) plywood (same sheet as mine)
Alternating grain going length wise for 2 layers and grain going width wise for 1 layer
Just used wood glue and lots of clamps, no vacuum bag
Very flexy
I didn’t ride it much, but it was too flexible for me to be comfortable standing in the middle of the board.
This is the first longboard I’ve ever rode and the only one so I can’t compare to others, but 5 layers of 1/8" plywood is definitely very stiff on it’s own. It’s also really heavy once the trucks and wheels are on there, so keep that in mind of you have to carry it.
It just occurred to me that I could leave the veneer off of one side, do the layup, and after the epoxy cures test it for stiffness. If it’s not stiff enough, just throw on some more epoxy, carbon fiber, and another piece of plywood, and vacuum bag it again. I don’t really have to get it perfect the first time. I feel better about that.
Since plywood is already alternating it’s direction on every layer, why do you still rotate it 90? Only sensible rotation for added stiffness would be 45 degree angle between veneers.
I have two boards, both used 3 layers of 4mm veneer with glass fiber coating on bottom. It’s pretty stiff, but you can still feel the flex in there.
The rotation was to help with stiffness over the curve, but you’re right, it’s pointless. That’s just what my shop teacher and I decided to do.
Cutting at a 45 uses a lot more material though. I was able to make 2 boards out of one sheet of 4’ x 8’ by sticking with 90 degree switches. We also only had the one sheet. If I did it again I would probably only have 4 layers and I might try angling the middle 2 at 45 degrees like you mentioned
My advice is to place the carbon fiber layers on top and bottom only, between Baltic birch and purple-heart veneer It will give you more stiffness…
Also I would make the deck in two step process…First glue the baltic birch layers together with carbon on top an bottom…then test it if it is stiff enough, if not, add more layers (but i think one on top and bottom will be much more than enough)…once you are satisfied with the results, just add the veneers
It will give you more stiffness…