Composite Sandwich Construction Start to Finish

[Surfdad]

The composite sandwich allows us to combine various materials as suits our purpose. Balsa is about 6 pounds per cubic foot. High Density foam can range from 5 pounds up to 20+ pounds per cubic foot. I had some extra balsa around, so I chose that for this build. MY rails will be 1/2 thick so I want to cut enough material for each side a total of 1". This is a stack of 1/8" Balsa sheet.

[Surfdad]

I use the masonite rocker template that I used to hotwire the rockerbed. It's not quite the same shape as the rails need to be, but is close enough after we bag the rails that it's not worth making a separate template.

[Surfdad]

I simply trace the template and then jigsaw the shape out of the sheets. I sand them pretty quick and they are ready for epoxying to the blank. There is one more decision that has to be made. The bottom skin can oerlap the rails or not. If you overlap the rails on the bottom with the bottom skin, the board will be stiffer, with less lengthwise flex. If you trim the bottom skin flush with the core, you'll allow some sheer and the board will flex more.

I want this board to be as stiff as I can make it, so I will overlap the rails with the bottom skin. I also prefer heavier rails, heavier in the sense that they are more hevay than the core. This extra weight on the rails, I feel, penetrates the wave face better and sinks easier for turns. Lastly, the balsa rails form a strong perimeter stringer system. It reduces flex remarkably compared to a single stringer down the middle of the board. Wood offers more rigidity than HD foam, but is harder to work with.

All of the sheeting trimmed.

[Surfdad]

The last thing that needs to be done is bevel the nose section on each of the rails pieces. These will meet at the nose and we want them to mate and form a flush joint, so I quickly sand the two sides at about 45 degrees...it's an ugly picture, but should give you the idea.

[Surfdad]

There are many folks that use balsa for rails in composite construction. It's easy to work with, high denisty than foam and readily available in appropriate sizes. There are also as many ways to attach the rails...saran wrap, bungee cords, offcuts with clamps. I have found the easiest and cleanest is to just bag it. Tomorrow I'll apply epoxy and bag the pieces to the sides of the core.

[Surfdad]

I thought this was interesting. The folks at Firewire have updated their site for their new Direct Drive 2.0 system. It features carbon rods that connect a high density foam and the fin boxes, along with tieing the tail up with cross members. The blue foam rails look like Dow HD insulation, which I believe is a 3# foam. Also the skin is core-cell a500 like we are using in this build.

http://www.firewiresurfboards.com/direct_drive.php

[Surfdad]

The rails are in the bag as I type this. This portion is a little tough to photograpgh because I have gloves on and epoxy everywhere Anyway, the details are a bit skimpy on this.

Principally, I paint on a thin layer of epoxy onto the blank on the rail, then also on to each succeeding layer of balsa. The same would be true if we used HD foam.

There is one step I forgot in the preparation of the rockerbed. When we bag, there is excess epoxy and we don't want anything stock to the foam of the rocker bed. So I use a section of linoleum that I purchased at Lowes for less than $5. Epoxy doesn't stick to the lino or polyethelene, so either of those materials would make a good barrier.

[Surfdad]

I use a disposable foam brush to paint the epoxy on and only about 2.5 oz of epoxy to attache the rails. Rubber gloves (the stuff in the pile) are HIGHLY recommended for this phase.

[Surfdad]

I put a few pieces of masking tape over the board to keep it and the rails in place while I slide the rockerbed and board/rails into the bag. Seal it all up and pull the vaccum.

[Surfdad]

This is a picture of the nose after I have pulled the vaccum, as you can see, it pulls all the rails pieces down and into the core. This does require some hand fitting as the bag tends to want to be pulled down between the core and the rails rather than pulling the rail bands IN towards the core. What I do is hold them in place, pulling out the excess bag material as the air is being evacuated from the bag. Once it's snug, I can let go and make sure the rest of the rail band is straight and tight.

[Surfdad]

The next phase will be to laminate the bottom skin to the core and rail bands. I will be using 3mm core-cell A500 for the skin for this build. I intend to attach the corecell to the core with 2oz glass. Hopefully the rails will cure by lunchtime and I can start the skin lamination after that.

[LovinPowell]

Lastly, the balsa rails form a strong perimeter stringer system. It reduces flex remarkably compared to a single stringer down the middle of the board. Wood offers more rigidity than HD foam, but is harder to work with.

Isn't that the principal behind the Firewire surfboard that Taj Burrow rides?

[Surfdad]

Hey LovinPowell, yep that's how the original Firewire's are constructed.

I do believe that Nev built the original board that Taj rides...and I also believe that it has a balsa skin, rather than the corecell skin, as is the case with Sunova boards and many of the boards from Nev's Speedneedle Surfboards. The other thing that Taj's board has is a shaped springer that is a free floating piece of wood running horizontally for a portion of the board.

[Surfdad]

I currently have the bottom skin in the bag. I had some BAG drama and so only got one picture of the corecell after I cut a section from it. What I did in this phase is cut a piece of corecell a bit oversize of the blank. Next I cut a piece of 2 oz glass the same size as the core-cell. I want to try and maintain a 1:1 glass / resin ratio so after cutting the glass I fold it and weigh it. It amounted to 1.3 oz. This would be less than 1 oz by volume, pretty hard to measure accurately. I went with 1.5 oz of resin by volume, which was the easiest "clean" amount I could measure.

Next I wet out the glass and smoothed it out on the corecell by hand. Next I laid the core with the balsa rails onto the middle of the glass corecell combo. Finally, I took all of that placed it on the rockerbed and slid that into the NEW FRESH bag.

The only picture I took - the corecell AFTER cutting the bottom skin.

[Surfdad]

Vacuum bags will eventually wear out. They develop small pinholes and the vacuum just doesn't develop. Many big name shops, swap new bags with each pull or board. Smaller folks like me, try to get 10 to 12 pulls out of a bag. When they fail, all you can do is swap them out ASAP.