Composite Sandwich Construction Start to Finish

[Surfdad]

I thought that I would, over some weeks, show all the steps in a composite sandwich construction board. I have two more that I have scheduled to build, so I'll show all the steps start to finish.

A composite is merely two or more different materials combined to create a structure. For thge purposes of this build I will be using a low density core 1# EPS foam, a High Density foam skin, no doubt 5# Corecell A500 in 3mm and then balsa rails, all connected with 2 oz fiberglass and the exterior will have 4 oz fiberglass, possibly carbon tape on the rails.

You'll start with some basic shape in mind The shape has two components the rocker - which is the curve of the bottom of the board and the outline which is what the board looks like when you are looking down and standing on the board.

It's not uncommon for folks to R&D (rip-off and duplicate ) an existing rocker and/or outline. For my build, I am modifying an existing design. I loved the board overall, but want about 1" more nose rocker.

So that will be my starting point.

To copy an existing rocker, if you don't have a template on paper or masonite, is to transfer the rocker onto paper. The easiest way I know to do this is to tape a sheet of butcher paper to a wall, then turn the board upside down and support it on a box so that the entire rocker is covered by paper on the wall. That is hard to explain, so the image:

[Surfdad]

You can see the butcher paper masking taped to the wall and the board that I am R&D'ing supported and pushed next to the paper. The entire length of the rocker has paper up against the wall. What I will do is draw on the paper and then cut that paper out using scissors. The curve that is left will be my rocker template. I draw the rocker on the paper using a sophisticated tool

Details are evident in the following picture:

[Surfdad]

Keep the level square to the board and wall and then simply pull it along the board being careful not to tip the nose or tail of the board.

Now on this rocker template I want 1" of extra nose rocker, so after I have traced the original rocker, I mark the nose and then measure an extra 1" down such that I have MORE curvature in the nose. I think merely free-hand the curve from the nose to a pont 12 inches back. I am careful to maintain the same basic curve, just a bit steeper.

Once that is done and you are satisfied with the general shape, using a good pair of scissors you can cut it out. Some folks leave the paper intact and just cut on the traced line. What we are going to do with this, is transfer the rocker to a piece of masonite. The masonite will then be used when we hotwire a rocker bed, the core/blank and if we do balsa rails, or even a high density foam rail.

The next step will be making the masonite rocker guides.

[Surfdad]

Transferring the paper template to the masonite is fairl easy. What we want, though, is two identical templates. When we hotwire the billet EPS, we need a guide on each side of the billet. The hotwire will rest on each template and that will give us a square cut.

So, toward that end, we cut two sections of masonite about 4" wide. Next lay then on top of each other and I fasten them to a solid workbench or suitable surface. Trace the paper template on to the masonite and then jigsaw the outline.

You want the rocker template surface as smooth as possible and that means SANDING! I start with 36 and work up through 150. The smoother the better with the hotwire. Any imperfection will cause the hotwire to stop and you'll burn a deep groove in the surface.

I use a sanding block and fast long strokes. Keep working it until it looks and feels burnished. Leave the masonite template fixed to the workbench until you have completed sanding.

The templates rough cut.

[Surfdad]

Still attached as I run through the sandpaper

[Surfdad]

Two identical bottom rocker templates ready for use.

[Surfdad]

I will use the masonite templates to hotwire a rocker bed out of 2# EPS foam. The rocker bed will be a tool that I'll reuse over the years. I will also use the template to hotwire cores out pf 1# density foam for composite construction. Lastly I like heavy rails for ding protection and also better wave face penetration, so I will use one of the templates as a guide to cut rails from balsa or a high density foam, running a razor blade along the template. The templates are also treated as tools and kept flat. I have a rack where I hang all the templates. I also label all the templates with the description and date.

Our next steps will be to hotwire. First the rockerbed and then a few cores.

[Surfdad]

I use a higher denisty foam for the rocker bed, in this case 2# EPS. When we bag the core, we want the bed to have a little more rigidity than the core. I acquired a 2' x 4' x 6" piece of 2# EPS and attach the templates to each side. I pick a point that is easily measure for the nose. Mark that on one side and then use some wood screws to attach the template.

[Surfdad]

The next measurement is another easily measured amount that gives me at least 1" at the tail. I typically use that 1" as the mark. I attach the tail section of the template and then one more in the middle.

[Surfdad]

Lift, flip, repeat Using the measurements for the first template attach the second template. Once that is done, stand the billet on end and on a slight angle. This will allow the hotwire to glide down the foam easily.

[Surfdad]

The rocker bed h'wired. Save the offcut as you can use that as a 2# stringerless blank.

[Surfdad]

We'll do the same basic thing for our cores, but will use 1# density foam for those. I buy in bulk 4' x 8' x 6"

[Jason B]

How bout some definitions--not sure what you mean by a rocker core vs. the rocker bed. Also, what's the hotwire (aside fromt he obvious fact it's a hot wire)-- is this a homemade tool or a commercially bought tool?

Very cool write up. I'm intrigued. I think you're making it look a lot easier than it really is though

Would using a surfboard blank be easier for a 1st timer trying to make his own board? Seems to me like I could shave a bit off the blank and have an easier time-albeit at a higher expense.

[Surfdad]

Hey Jason,

I don't want to mislead anyone, the composite sandwich construction is WAY hard. However, if you've shaped a board, it's manegable. It's also substantially more expensive than shaping a blank. The one thing that the composite construction offers, is an engineered construction. Differening materials in seperate areas to give the ride you want.

In order of "ease", IMO:

PolyU blank with Polyester resin to laminate the glass is the easiest and it will give a great ride. It's easy enough to do that anyone with basical hand tool skills can shape a board. It's also fast. You can shape a board today, glass it tomorrow and ride it the following day.

The next would be EPS and Epoxy. Epoxy is less toxic, but IMO is also harder to work with than Polyester. Gloss coats with Epoxy require some experience and skills. A polyester gloss coat is pretty easy and looks good in comparison.

The hardest is the composite sandwich construction. Specialized tools like the hotwire and vacuum bag system. Not impossible, but it's an acquired skill.

Hopefully I'll get into some more detail as we go along...I am basically just showing all the tools and supplies that are needed. TONS left to cover.

[Jason B]

Any source you prefer if I was to buy a PolyU blank?
I haven't used polyester resin yet-only West systems 105/206 and another off brand (that I'll never use again).
I appreciate your taking the time to write this up!! It's neat to see it done, kinda like the How it's Made show on Science Channel