Hollow wooden kneeboard

[Headwax.]

could be relevant

man not happy tho

http://www.hollowsurfboards.com/how_to.htm

[Jon Manss]

If it is worth any thing Tom, I would chose a stringer or vertical support. Remember where your planning to surf. Also the plywood is far supior to wood strips for strength. A thin skin can be bent and glued out of one piece. It may not look as nice but your after strength here.

[tomway]

Headwax: Yes beautiful aren't they! As I said in my opening post Paul Jensen was the person who at least brought the hollow wood surfboard into public awareness, and developed the method that many seem to be using (all this information can be found in posts on swaylocks). His boards really are works of art. I think Daniel Hess's boards and philosophy of design looks like it could be better applied to kneeboards though, and his site is definitely worth a look. As posted before www.hesssurfboards.com

[tomway]

Hi Jon, I think you're right, but I'm still intrigued about how the flex characteristic of a totally stringerless wooden board might contribute to handling. The solution is simple really I guess.... as I prepared rails for two boards I've decided to do one with a stringer and one without, then see which goes and lasts best.

... or, how about a stringer that is only attached to one skin, so it still allows shear movement between the top or bottom skins and some flex, but supports the deck in compression. Think I might need to sleep on it another night!

[frankfqr]

Perhaps small I beams attached only to the center cross beams at a location approximate to your knee dents on your foamy. At least you will be able to positively transfer your turn "G's" to the rail instead of just merly compressing the surface skin. I'm not thinking full length, just knee location. Also at this junction you you might want to consider your preference for a crowned deck or "scooped" in the knee area because you sure won't get the time worn dents with this construction. Anyhow, looking good and thanks for posting the progress!!!

[Man O' War]

Hi Jon, I think you're right, but I'm still intrigued about how the flex characteristic of a totally stringerless wooden board might contribute to handling

Tom, when you're considering flex, keep in mind that it works if the degree of flex increases as you go from front to back and sides to center. Remember markgnome's well worn comparison of the tuning fork. That's why Loehr has been experimenting with peripheral stringers. Otherwise, if the flex is sort of uniform throughout, instead of flexing and torquing, your board will bend and bog. That's not what you want for a masterpiece like this.

I'm enjoying your work, your pics, the comments from friends, and your thinking out loud.

[tomway]

A slight sidetrack. In conversations with my friend Eko he would often tell me about a number of different trees that grow around his village in the mountains. He reckons that some of them are extremely light in weight and pale in colour. There's about 5 different species, or varieties that he reckons would be good for wooden board projects. I'd asked around this part of east java for the trees he named but no one had heard of them. Obviously a local name/dialect. To cut a long story short, he came back with a sample today:






... now if I'm not mistaken, this is balsa

Eko says it grows extremely quickly and has a long straight trunk. Apparently there are a number of varieties, all of which are extremely light in weight. He disinguishes them by colour and whether goats like to eat the leaves. The sample in the pics apparently makes very good goat fodder. The wood is only every used for supporting floors when cement is layed in construction, is plentiful as its not favoured by the timber trade here, and extremely cheap. A big tree, he says, would cost about two million rups (about 200 dollars). Milled into planks, 21 cm wide and 2 cm thick, the net cost works out at about rp 7,000 per metre. In other words, 70cents.

The name Eko gave this sample was 'besiat', and another tree he reckons is similar (but that goats won't eat) is called 'sengon laut'. Any of you wood people heard these names before? Can anyone describe a balsa tree for me?

[scoop]

Tom
this is an excerpt from a page I found

Balsa trees grow naturally in the humid rain forests of Central and South America. Its natural range extends south from Guatemala, through Central America, to the north and west coast of South America as far as Bolivia. However, the small country of Ecquador on the western coast of South America, is the primary source of model aircraft grade blasa in the world. Blasa needs a warm climate with plenty of rainfall and good drainage. For that reason, the best stands of balsa usually appear on the high ground between tropical rivers. Ecquador has the ideal geography and climate for growing balsa trees. The scientific name for balsa wood is ochroma lagopus. The word balsa itself is Spanish meaning raft, in reference to its excellent floatation qualities. In Ecquador it is known as Boya, meaning buoy.
HOW DOES BALSA WOOD GROW?

There is no such thing as entire forests of balsa trees. They grow singly or in very small, widely scattered groups in the jungle. For hundreds of years, balsa was actually considered a weed tree. They reproduce by growing hundreds of long seed pods, which eventually open up and, with the help of the wind, scatter thousands of new seeds over a large area of the jungle. Each seed is airborne on its own small wisp of down, similar to the way dandelion seeds spread. The seeds eventually fall to the ground and are covered by the litter of the jungle. There they lay and accumulate until one day there is an opening in the jungle canopy large enough for the sun's rays to strike the jungle floor and start the seeds growing. Wherever there is an opening, made either by a farmer or by another tree dying, balsa will spring up as thick as grass. A farmer is often hard put to keep his food plot clear of balsa. As the new balsa trees grow, the strongest will become predominate and the weaker trees will die. By the time they are mature, there may be only one or two basa trees to an acre of jungle.
HOW LONG DOES IT TAKE A BALSA TREE TO GROW?

Balsa trees grow very rapidly (like all pesky weeds). Six months after germination, the tree is about 1-1/2 inches in diameter and 10 - 12 feet tall. In 6 to 10 years the tree is ready for cutting, having reached a height of 60 to 90 feet tall and a diameter of 12 to 45 inches. If left to continue growing, the new wood being grown on the outside layers becomes very hard and the tree begins to rot in the center. Unharvested, a balsa tree may grow to a diameter of 6 feet or more, but very little usable lumber can be obtained from a tree of this size. The basla leaf is similar in shape to a grape leaf, only a lot bigger. When the tree is young, these leaves measure a much as four feet across. They become progressivly smaller as the tree grows older, until they are about 8 - 10 inches across. Balsa is one of the few trees in the jungle which has a simple leaf shape. This fact alone makes the balsa tree stand out in the jungle.
THE PERFECT NURSE!

Nature evidently designed the balsa tree to be a "nurse tree" which would protect the slower-growing species of trees from the scorching jungle sun during their critical early years. For instance, in an area of the jungle that has been ravaged by a tropical storm or other natural disaster, the balsa trees will quickly sprout and begin to shoot up to impressive heights in a very short time. Their fast growth, and the extra large leaves they have in their early years, provide shade to the young seedlings of the slower-growing forest giants. By the time the seedlings are established enough to take care of themselves, the balsa tree is beginning to die. Undoubtably, the balsa tree's rapid growth, fast spreading crown of first very large and gradually smaller leaves, and it's relatively short life span were intended to make it the "perfect nurse" in the jungle ecosystem.

[scoop]

Tom
It could be an imported "weed" that likes the area
Sounds very simillar to natural growing area
Basically the faster a tree grows ... the softer the structure .. hence lightness in weight
But it is still classed as a hardwood because of the grain structure ...unlike softwoods (pines)
Tony

[tomway]

Hi again! First, thanks for all the ideas on design, there was a fair amount of mulling (in the non-australian sense of the word) to do before I did any more work. Scoop, thanks for the info you gleaned on balsa. I've since spent hours scouring articles on the web and find no mention whatsoever of balsa in Indonesia. And yet I would bet my left swim fin that's what I've got... perhaps you're right, this is a foreign plant that got introduced recently, but it seems strange there's such a large quantity. Cheers anyway.

MOW: the tuning fork metaphor, that is a good one isn't it, and it prompted me to reread all the flex-spoon thread from last year too. Took a fair while! Thanks Frank too for your comments.

In the end I tried to encorporate all the ideas. From the nose of the board to slightly forward of the wide point I installed an eps stringer with wood skins either side to create some stiffness and prevent the 'bogging' that MOW mentioned could happen if the flex was in the wrong place. Under the knees I also used an eps/wood sandwich for the stringer, but the wood only extends about an inch down, leaving I hope the remaining eps a little flexibility. From the knees back I've put in an eps only stringer as this is where the flex seems to be most beneficial.

The next step was to make the skins. I went with Jon's preference for plywood. Finding good quality plywood was a mission in itself and took me to factories all over this part of east-java. To cut a long story short, no one would sell me the good quality (and nice looking) stuff as it was all being exported to America and Europe and would breach their contracts. I could get some nice teak veneers but the oiliness in view of lamination put me off so I went for a wood called 'sungkai', very pale with a marked pink, dead straight grain. Pretty boring but it was lightish and strong.



Then I cut the skins for the deck and bottom, a little oversize.



The skins fit into a 1/8" recess routed into the rail and tail sections. They needed alot of repeated measuring, sanding and planing to fit.



I glued the skins in with 'liquid-nails' which I found in a local hardware store. Its a brown coloured, bond anything kind of cement that fits in a caulking gun. Then I clamped the skins down from the centre out. The bottles of aqua are keeping the concave in over the centre cross members.



Weight pre-rail turning, 4kg. Hopefull lose 1/2kg on that before glassing.



After nearly 4 weeks of solid work, I've got a hollow wood blank. Polyurethane seems so cheap!!



The wife decided to give it a strength test



Yes, she's a goofy kneed sofa-surfing rail-grabber! I'm so proud

Hopefully start turning the rails over the next few days. Got to decide what tool to use for this. My feeling is to go with the handplanes, but I have more experience with an electric planer on foam, so am still unsure.

Tom

[Jon Manss]

Beautiful job Tom. I think I mentioned to you that hand planes work really well on convex surfaces like your rails. Just remember to follow the grain from mid point to tail or nose. That way you won't chip or split the grain. You will also notice how forgiving a plane can be. It wants to cut smooth lines. Make sure the knife is sharp and have fun. Thanks for sharing this project. You have documented it well and it has been fun wtching the progress. Jon
BTW Teak is hard to finish I here an accetone wash helps with bonding.

[Man O' War]

[skansand]

uh oh manowar..
thou shalt not steal emotocons from the groms......... ......you must be a dropknee'er too!!!!

[Man O' War]

Busted

I just like Tom's work!

[tomway]