After a host of setbacks I finally am going to split my board this spring and have an idea I want feedback on.
After splitting my board, instead of just epoxying the new inside edge, I want to use a layer of carbon fiber to help stiffen the board. The way I am thinking about it is the following:
1. Split the board in half 2. Take a secondary cut on each half at a 45* angle (Right most picture) 3. Remove a 1-2 cm of the top sheet from each side (red line of left most picture) (I imagine this step would be quite hard so I probably would end up just putting the CF over the top sheet, but it would be nice if the CF was semi flush with the top sheet.) 4. Replace top sheet and inside edge with layer of carbon fiber (CF would be placed between the red lines in the middle picture)
To layer the CF you could either do each half individually or you could clamp the board together, layer the CF then, after it cures, cut the board down the seam again. Either way you did it you would then sand down the excess to create a better fit. Thoughts? Comments?
Issues I am worried about are – 1. Making sure there is a full seal between the base and the new edge. 2. Actual amount of stiffness provided form 1 or 2 layers of CF 3. Flex of the CF along the axis where the 45* cut meets the top sheet. Worried it might be more prone to cracking.
No guarantee I will actually do this, just an idea I am throwing around in my head. LMK your thoughts. Really trying to figure out if this just a crazy idea that is a waste of time vs the conventional way.
Joined: Wed Mar 23, 2005 10:05 am Posts: 1538 Location: Colorado
I put uni carbon on the inner edge of my furberg when I split it. I just cut the board, then sanded the inside edge to a perfect square using aluminum angle stock and 60 grit sandpaper. Then I laid down one layer of uni carbon fiber tape tip to tail along the edge. After a slight cure, I continued to further seal the carbon fiber and level out the fibers by laying down a few layers of epoxy with graphite powder in it for increased durability. I then trimmed the edges even with the base and topsheet, and sanded smooth. This approach was a lot of work, but has proven to be very durable. I used WEST 205 epoxy with the long cure hardener, and WEST graphite powder.
1. You want to use 3 K Carbon tape because if you cut regular weave or 2x2 twill the edges will instantly fray out once you cut a 3/4 inch strip, this will be a disastrous mess.
2. even in the form of carbon tape, you will have a very hard time laminating it over the curve without the help of taping or vacuum bagging because the carbon will keep trying to spring back up off the wood. You'll probably have a hard time with the glass too if you haven't laminated surfboards or something similar before. Definitely round the top edge, a hard corner will be harder to laminate
the cheap route: tape over the part of the top sheet where you do not want carbon, start the edge of the carbon tape on the rail brushing epoxy resin onto the fabric as you go ( have the board at a 45 degree angle. after you brush a few inches on, take strips of wide clear packing tape attach each strip to the base and then wrap it up over the laminated carbon on over onto the deck of the board. This will leave a nice smooth finish on the rail.
Consider this: Carbon is better than fiberglass in that it doesn't stretch as much as glass, but wrapping the rails and deck will cause mostly compression of the fiber as the board flexes. Fiberglass and Carbon are pretty much the same in resisting compression. If you used good quality S-2 fiberglass you would get essentially the same result, but you'll probably end up buying whatever you can find in the right width of tape. Laminating over a curve on the rail should add a fair bit of stiffness, just like folding a piece of paper will versus keeping it flat. I would go with one layer of 3K by 3K Carbon or one, maybe two layers of 4oz S glass. While not as stiff as toughened ski/board epoxy, surfboard epoxy is super clear, cures at room temp and won't yellow with time in the sun.
Thanks to both of you for the advice/tips. The tape is a great idea. After I posted this I called a friend who makes one-off CF parts for race cars and he offered to help me with this. Will post updates when I get this all together (won't be until spring).
Joined: Wed Jan 04, 2012 2:59 am Posts: 278 Location: Amsterdam
I'm all for a bit of experimenting, but I have some doubt on how much stiffness this will bring. Yes carbon fibre is pretty stiff, but not in the way you're plannning on using it. A carbon fibre (or fibreglass) board get's most of it's stifness from the TWO layers above and below the woodcore. In any sandwich construction, the thickness of the core will be a huge factor in the stiffness. So a very weak core that is an inch thick with two thin layers of carbon will be much stiffer than a "1/4 inch core with very heavy carbon fibre on both sides.
I'm not an expert like your friend who does this for a living, but i've build some carbon fibre parts myself (search the forum) and a few prototype boards too.
If you just want to regain the original stiffness of the board you could consider inserting carbon fibre strip or tubing into the sidewall or even just on top of the board. Dragonplate has this in many forms and it should be less messy and stiffer than your original idea. You could use a simple router to make a groove and laminate the strip directly to the woodcore.
Also in most DIY builds you will lose more torsional stiffness, the loss of stiffness lengthwise is a lot less of a problem if done right. You want the boardhalves to be very solid when put back together. If they have very little play and movement, you will get pretty close to how your board was before cutting it. A pair of good bindings and a precise fit will help a lot with that.
Joined: Wed Mar 23, 2005 10:05 am Posts: 1538 Location: Colorado
I did not take any pictures of the process, as when doing a wet layup like this, all of your hands are full. Here is what I did:
1. Went to Keffler's place in Evergreen and used his table saw and jig to make the cut. 2. Back at my place (Phantom High Altitude Research Center, aka Ice Station Zebra) I used a piece of aluminum angle stock as a sanding block, and sanded the cut edge to a perfect 90 degree angle with square edges, using 50 or 60 grit sandpaper: you want everything to be square and rough, so the epoxy has something to key into. 3. I placed the board half into a stand I made, which held it perefectly vertical and level, to make a flat, level surface of the cut edge. 4. I used uni directional CF tape, 1" wide, purchased from WEST Systems (not anything woven, which would be weaker, and would not have as much longitudinal stiffness). I precut a piece of this tape to length and set it aside. 5. I enlisted a helper. Then I mixed up some WEST 105 epoxy with the long cure hardener. 6. BTW, the topsheet and base of the board were well masked off at this point with blue painters tape. 7. I laid down a layer of epoxy on the cut edge using the spatula method. 8. The helper and I laid down the CF tape on the edge, working out creases and bubbles with a spatula. It was a little tricky getting the curve to the tip and tail to lay down flat, but possible. The fairly gentle curve on the furberg probably helped. I made no attempt to wrap any CF over the top sheet or base. 9. I added more epoxy to fully wet out the CF, with spatula. 10. I had preheated a small bathroom at my place to over 100 degrees using a small space heater, I placed the board in there to allow for the initial cure. 10. After the initial cure, but before the full cure, I pulled the masking, and (rough) trimmed the edges back using a sharp mat knife. 11. Before full cure, I mixed up more epoxy, and added WEST graphite powder. About three coats of this was applied over the CF for additional protection and to fill any fiber gaps. 12. Put the board half back in the heat and allow for full cure. 13. Sand the edge smooth, and sand the edges at the base and topsheet with a very slight bevel. I was very careful when sanding this bevel to not sand through the bond between the CF and the base top sheet.
The addition of the CF sidewall definately added stiffness to the finished split halves. I suspect the added stiffness is more a result of the mechanical joining of the top fiberglass layer to the bottom fiberglass layer (creating a torsion box on the inside edge) than a result of the added carbon, but it is just speculation to say.
This was a lot of work, and was tricky to pull off, but I am happy wiht the results. The board rides great, and with 20-30 days on it, no problems so far. If I were to do this again, I would probably make a press, with smoothly finished inner face, and then I could do the layup in one single step, rather than adding the additional layers of epoxy. BTW, if I was doing a DIY where I just wanted a bombproof finish on the inner edge, I highly recommend WEST 105 with added graphite powder, this stuff when cured is super tough, and also very low friction. The WEST Industries website is a great resource, with lots of instruction and tutorials for those interested in learining about various glass and carbon layup techniques.