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:)

[Surfdad]

Polyester is very easy and you can find water white clear for surfboards at TAP that is actually quite good. It does require the use of a respirator. The fumes are toxic even in a ventilated area.

My two favorite sources for supplies are:

http://www.fiberglasssupply.com/

http://www.foamez.com/

The folks at Foam EZ are hands down the best to work with. If you have an issue, they'll correct it without hesitation. I ordered a set of Futures Quad fins and one of the trailers was wrong. I shot them an email explaining the issue and they overnighted me the correct fin and asked if I could return the other one, if not that was ok. GREAT cutomer service. They also have complete board kits - includes everything you need to build a board, save for the tools.

Fiberglass Supply is cheaper but not as helpful. They also have a much more extensive inventory of products.

[Surfdad]

Back to the build after a night off :) I had that scheduled. :)

Starting with the core which I hotwired yesterday, I draw a centerline. Typically blanks have stringers down the middle so we don't have this issue, but our composite build requires us to do that. I use a 4' carpenters square for this.

[Surfdad]

I make a master template out of foam. Most professional shapers use masonite to store the outline shapes. I only have two basic shapes, so...I just cut and save the entire outline in 2# foam.

[Surfdad]

I center this outline on the CL I drew on the blank and then trace this on the blank.

[Surfdad]

Many instructionals and books describe using a handsaw to cut the outline, but I am lazy :) So I just breakout a jigsaw and cut on the line, slowly and carefully.

[Surfdad]

Typically the cut is square, but if it's a little off I straighten the cut with a surfoam.

[Surfdad]

The composite sandwich construction requires that you build from the inside out. I want to connect the rails to the fin boxes and I'll do that with a carbon tube. More over the weekend.

[Surfdad]

As I mentioned in the post above, you build from the inside out. I wanted to add a small bit to connect the rails and the fin boxes. That requires that I install that bit before the skin goes on. It's a lot like assembling a motor, the bits and pieces must go in before buttoning up the cases.

The carbon tube does a few things. One is that it stiffens up the tail, another is that it helps prevent twist-off of the board. IMO the biggest loads we have behind the boat are rail-to-rail and this longitudinal member helps minimize that twist.

The tube I am using is 1/2" OD, so I make my cut 1/2 x 1/2. In this way, when the tube is seated the top will be even with the bottom of the core. When we go to skin the blank, if we have anything standing proud, it will cause a "bump" on the skin that will need sanding.

I use a Kyobi laminate trimmer for this sort of freehand routing. The tool is light and easy to manage, plus it has a see thru plastic stand so that you can see what you are trimming.

[Surfdad]

Slot routed and the Carbon Tube trimmed and shaped along the ends to fit in the slot connecting the rails and boxes. I have measured the location of the carbon tube placement such that when I route the fin boxes in, later, the leading edge of the boxes will just nick the carbon tube. Then when I epoxy them in, I'll have a single mechanical piece.

[Surfdad]

As you would expect, the slot I routed is square and the tube, by definition is round. I fill the corners with a slurry of epoxy and microballoons. The microballoons make the epoxy thick, but also allow some ability to sand. Epoxy, when cured, is extremely hard and that makes sanding difficult. There are a bunch of products on the market, but TAP plastics is very convenient for me.

The mixture should look and feel like peanut butter, almost.

[Surfdad]

Next I slather an ample amount of the slurry in the slot, being sure to coat the sides well. Then fit the carbon tube to the slot, aligning the edges so that the cut is flush with the rail outline. Finally, using a scraper I fill in the voids so that the slurry is flush with the core. I want that smooth, without excess epoxy and also, without any voids.

[Surfdad]

The temperature here is pretty cold at night. The epoxy I used for this requires a minimum of 50 degrees to cure, but works best at 70 degrees. I have a hotbox which maintains heat anywhere up to 100 degrees F. So I toasted the board. :)

[Surfdad]

The next phase will be to attach the rails. We are off snowboarding today, so hopefully I will get to that tomorrow.

[dogbert]

I like it, a toasted peanut butter board ;)

[Surfdad]

Dog you're fuuny! :)

[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.

[Surfdad]

Out of the bag, the bottom skin is attached. I got two quick pictures out of the bag. The corecell is a light yellow and somewhat tansparent.

[Surfdad]

I use a 1/2 roundover bit in my router to trim the corecell and also shape a large portion of the rails. I leave the rails sharp from about 6" in front of the fins through the tail. I use a razor blade and sandpaper for that section...blending the two areas with sandpaper.

[Surfdad]

The bit I use has a bearing on the tip, so I just run that up on the balsa rails and the skin, glass and balsa are all trimmed up nice and neat - what the ut looks like and the trimmed board.

[Surfdad]

Back on schedule, I shaped the deck and rails this evening. I still have a little touchup, but the board is ready to have the deck bagged.

I used three basic tools. The Planer to make BIG cuts. The surfoam to roughly shape some and smooth the deeper cuts., the block plane to shape the balsa rails.

I still need to sand a bit to blend things, but it's close.

[Surfdad]

Back to it - I got distracted with a molding project and helping someone with some testing.

I attach the top corecell with 2 oz glass - it asctually weighs 2 oz. The best ratio of 'glass to resin is 1:1. That allows for the least weight and gives a strong, stiff lamination. Too much 'glass and it's flexy, too much resin and it's brittle and heavy...so...1:1. Not folks that have laminating experience are probably wondering how to spread 2 oz of epoxy! :) I basically just fold the cloth up and stuff it in the mixing bucket, absorbing the 2oz of epoxy.

The corecell attached to the blank with the glass and epoxy underneath.

[Surfdad]

Vacuum pulled - if you look closely the surface is smooth as glass. That's a fresh bag and THIS is the key for external lamination...start with a fresh bag.

[Surfdad]

This time of year it's pretty cold. Epoxy needs heat to cure and so I maintain that heat by covering the bag and rocker bed with an electric blanket :) My Walmart autoclave. :)

[Surfdad]

Out of the bag and ready to be trimmed. The corecell is pretty easy to work with. I'll trim it close with a single edged razor and blend it with 60 grit sandpaper.

I have to bag a d-cell skin this evening on a separate board, so it may be a few days before I get to the carbon fiber tape over the rails.

[Jason B]

I thought you dropped this project. Nice to see you didn't, it's neat to see it done! Keep going;)

[Surfdad]

No, I'm still working on it. This will be my board this summer, so I want it RIGHT! :) Just a few more steps and this one is finished, but I'm turning into a slowpoke these days.

[Jason B]

It happens...I'm going on week 2 now for installing hard wood floors in a bedroom and hallway. I could never do this for a living, my whole damn body is sore after a day of doing it! WHITE COLLAR baby:ro: :p

[Surfdad]

I hear you Jason - manual labor wipes me out too!

Two quick updates. The Corecell skinned board is trimmed and blended. This is an easy job. I just run a single edged razor along the rail and then use a sanding blocl to blend the skin into the rails.

The next stage is the carbon tape on the rails.

[Surfdad]

The other thing I was doing this evening was bagging the top skin on a quad square tail. This board has a single to double concave, whereas most of the other projects have a simple flat bottom. When I have been bagging the other skins, I've been using the rocker bed. This quad has a full basswood perimeter stringer. When you hotwire the rocker it will stay during a bagging, especially after laminating at least one skin and the rails.

The quad in the bag without a rockerbed.

[Surfdad]

Carbon Fiber tape bagged on the rails. The balsa tends to be bouyant, and that gives the rails a "corky" feel. The Carbon stiffens up the board as well as reducing the corkiness of the rails. This board, when finished, will weigh in around 4'ish pounds and is exceptionally bouyant. When you fall, it will typically shoot 12-15 feet in the air (and 40 feet away!!!!!) :)

The edge is a bit rough, but I will cover that with a pin line or a pattern that blends the carbon and corecell. It's almost impossible to do a cutlap under the bag, or at least I haven't found any good way. Things behave very differently in a vacuum.

[Surfdad]

The carbon up close.

[Surfdad]

Out of the bag and ready for the final external lamination and sanding. The board looks like this:

[Surfdad]

The nice pinlines that you see on custom made surfboard are design to hide the transition between the laps and the rest of the board. :) I am NOT an artist and my etch-a-sketch is still in use this morning. :) The concept will be to paint some broad design to hide the transition from the carbon to the corecell - something like this:

[Surfdad]

A few points I wanted to touch on in applying a rail tape like this. I didn't get good pictures, but I used a wetout table to get the carbon wet with epoxy before laying this on the board. There are a few ways to apply a laminate, one is to drap the textile on the board and then pour resin out and spread it. This is the typical process for Polyu boards. Carbon is a little tougher to wet out and you can't really work epoxy into a textile, it tends to FROTH when worked too much.

A wetout table can be constructed in any number of ways, but I simply use an appropriate length of plywood and then I drape a sheet of polyethelyne over that. Literally NOTHING sticks to polyethelyne. Also, the Polyethelyne acts as a barrier, so as I am pouring the epoxy over the carbon tape, it stops at the plastic and so soaks both the top and bottom of the tape.

I did one tape at a time, wetting out and then laying up on the board.

Carbon CAN be significantly stiffer than fiberglass, but a great deal is dependent upon the resin used to laminate the Carbon. You want to use a resin that has a HIGH modulous of elasticity - that is to say when cured it's STIFF. I used TAP plastic's SUPER HARD 4 to 1 epoxy to laminate the carbon over the rails. Which, if I haven't mentioned it before is one of the benefits of building a comosite sandwich...you have the freedom to choose the materials inclusive of foam, textile/fabric, resin in various compartments of the board. Resin infusion which tends to be considered more advanced, you don't have the luxury of choosing resin. As such, for a resin infused board, the entire construction will have the same resin. Whereas, when bagging, we can use one resin for the bottom skin, one for the top, another for the rails, and still others for the external lamination.