The top skin seemed very stiff, so I cut grooves along the edges where it will have to bend around the rails. I used a flat piece of aluminum as a guide for my dremel and I used the jig that allows the dremel to set the cut depth. Made grooves about 1/4" apart up to 3.5 inches from the rail. Last week I was checking on my vacuum pump and found that it is broken, so I have to wait until I can use my brother’s pump. In the mean time I remembered a post from my mentor BB30 showing how he bends balsa strips around curves. I decided to give it a try and sprayed the balsa with water then taped it down onto the board. Came out pretty good except the nose. I can cut better grooves and fix that later.
Then I took the left over 1" and 1.5" foam and started a 8’ mini mal build.
We normally use a surfboard we like as the rocker table and keeping the foam full thickness we can press the rocker in by placing the deck side of the foam against the donor board’s bottom. The vacuum bag force is more than enough to pull the bottom skin down and duplicate the donor board’s bottom contours.
This second board I’m doing is a little different because I want to have either a slight roll or a beveled edge on the bottom (like a Stewart Hydro Hull). I don’t have a board with the bottom contours or rocker I want, so I made myself a second rocker jig that is a mirror image of a rocker table I already have. It simulates the bottom side of a surfboard, but like the first rocker table, it’s flat, no concaves, or roll. It will allow me to shape the bottom then attach the wood skin. I decided to glue the rails on early in the build to have a blank with the rocker locked in. I had already cut out pieces of 1/8" plywood with the correct rocker, so I glued them on with tape and shrink wrap, and I have the foam secured in the rocker jig. We’ve used the tape and shrink wrap to attach wood skins in the past, so if you don’t have a vacuum bag system, you can still get by. I use bricks, tape and shrink wrap a lot. I’ll need to use a vac bag later because I don’t have a jig with the contours I’ll be using and the skin won’t press down as accurately with just weights.
I should note that the rocker tables I have won’t fit into my vacuum bag, but my brother made a jig that has the same curve on each side and it fits into a vac bag with the board. We place the foam deck side against the jig to do the bottom, then later place the bottom side against the jig to attach the deck. Works great, but I’m using a different rocker right now. I gotta admit that making these boards is way more hassle than buying a surfboard blank, shaping it, then glassing it without a wood skin. But, we’ve made some very light yet durable boards using this foam and 1/8" thick Balsa wood.
Shaped the bottom with a slight concave and chines, then taped up a simple 1/16" thick balsa skin. I You can see the balsa strips that will help hold the single fin box in place.
Spent half of the day getting vac pump working again. I used foam glue and a vac bag to attach the bottom skin.
Board is out of the bag, but needs to have the deck shaped. Before and after shots of the deck. Next step is to make the top skin, but today the weather is nice so I have a lot of yard work. It was supposed to rain hard again late in the afternoon, but it didn’t. Oh well, spent the day mowing 2 yards with very tall grass and weeds.
After the deck skin is glued on, I will add an inch of XPS foam all around the board then shape the rails. I want the deck skin to overlap the wood rail band, so I add the last part of rail after the deck skin is attached. Then I’ll add wood nose and tail blocks, then it’s on to glassing.
I got the deck glued on and trued up, then I added a rail band of blue Dow styrofoam about 1 1/8" wide. Used stretch wrap and tape to glue it on. Then I tapered it down to the same size as the rails, and sanded the skins since they were pretty rough. I also made wood nose and tail blocks.
Next up, I’ll shape the blocks then final sand the wood skins then turn the rails.
Finally got the deck skin glued on with the vac bag. I actually did this before the board with the blue rails. I started adding the rest of the wood rails on this board with carpenter’s wood glue. Depending on how it looks, I may or may not need another band. I still need to make a nose and tail block for that board, but I usually let the glue dry 24 hours. I’ll get pics of that board in progress tomorrow. I work on one board until I have to wait for glue to dry, then I work on the other board. I left this one at my brother’s house to do the vac work, but since I fixed my vacuum system, I brought it back and did the deck skin myself.
I use polyurethane glue like gorilla glue or epoxy to glue the skins to foam. I used to use 5 min epoxy to glue wood rail bands to foam, but I used poly glue for the last several builds to help fill any voids. I use carpenters glue, not the white glue, it’s a yellowish color to glue wood to wood. The carpenter’s glue id not good for foam. Best glue is the polyurethane glue. I’ll shoot a photo of the glue later today when I get shots of the board with wood rails.
Aloha Sharkcountry, do you allow for any spring back when using your rocker table? How much movement is there after releasing from forms? Is it significant enough to pre-plan for, or can it be done with a final sanding?
If we don’t add the rails right away, the foam will flatten out. Once a band of wood is glued to the rails, the foam will hold the rocker. I added a piece of 1/4" thick wood under the nose when I did these boards and when I lay it on the rocker table it still has that extra bit of rocker.
In hindsight, this process is time consuming and a lot of work, but if you want to do veneers, vac bagging is probably the best way to do it. If you don’t mind the extra weight, using thin plywood would make it a lot easier and faster. Model airplane Balsa works great, but it only comes in 4’ lengths. To use the fancy woods, I really need more equipment. My brother has a thickness planer and a joiner, but trying to coordinate time to use them is a hassle. I could use a thickness sander as well because the planer tears some of the woods we used. I also need to re-calibrate my vacuum pump. The gauge is not working, and whatever it was set at is a little too strong for Home Depot foam.
Here’s the board with the wood rails. I try to cut the strips as close to the width I need, but this board has so much curve my pencil couldn’t get all the way in to mark the wood. I used some 1/4" thick wiliwili for the straighter tail section and balsa for the rest. You can see in some of the photos that I had to cut away quite a bit of wood. I used a razor knife and several small hand planes to work it down to match the board. I cut out a nose and a tail block for this board, and glued it on with poly glue.
Back to the blue rail board. After the nose and tail blocks were glued on, I drew outline then cut it out and went to town shaping the nose and tail blocks, then turned the rails, and sanded the big scratches out of the top and bottom. You can see the cuts I made to help the foam wrap around the nose.
Depends on what wood I use. I have a stash of Balsa sticks that are 1/4" x 1/4" from 18" up to 48" long, and others that go all the way down to 1/16" x 1/16" x 18". Those will bend most curves, but I have to use up to 5 strips to get a single band. With the sticks, I just tape them along the rail following the curve of the outline and rocker.
For single piece bands, we cut the rocker and use the outline to get the shape right. I’ve been using heavy paper or poster board and make a template of the bottom rocker. My brother makes his first band the full thickness of the blank, but I made mine about an inch and a half. There’s less to cut later because the thickness of my boards at the rails are about an inch or just a bit more. We’ve also been using 1/8" plywood for the 1st band, but any wood would do. I think a solid wood is better because ply tears when you plane it. I made a few bands of redwood recently, and at 1/4" x 1/4" it will bend easily. For wider pieces, wet it, and it will bend, or make it thinner. At 1/8" most lighter wood bends quite a bit, but you can usually only bend it around one curve and the boards have 2 curves.
These boards are being made much more complicated than it could be. If you us a simple skin, like a full sheet of thin wood, you don’t have to mess with piecing together a bunch of small pieces. You can use another board as the rocker table, if you have a board with the rocker you want to use. The trick to using another board is to keep the sheets of foam full thickness, and place the top of the foam against the bottom of the board. If you profile it, it will change the rocker, so you have the ability to use a board and make a different rocker, but you have to plan it out.
Balsa is easy to work with because it is soft, you just have to go through it and organize the pieces that bend the most to the pieces that don’t bend easily. If you cut a bunch of grooves into a sheet of ply, you can get it to bend around different curves. I just think the plywood is too heavy, but it makes a solid board. Woven 4’ x 8’ bamboo sheets work well too, they make really strong skins, they are light, and the sheets are very flexible.
Charlie, you taught us how to do this. We just added the Home Depot foam to the mix.
You are the master, we’re still students. Thank you for all the time you spent teaching us, and all the stuff you gave us over the years.
Added a Wiliwili nose block and Koa tail block on board one. Shaping is done. I need to do a seal coat then I’ll glass it. I glassed board 2 and after doing that I realized I should do the seal coat first.
