I had a bit of an idea today.
I get blocks of eps 250mm x250mm x 1000mm at work so I was thinking if i made ribs like a hollow timber surfboard construction at these cross sections of a board & cut them out perfectly & say glued them all together with expanding foam maybe to fill the void were the ribs go & have say a couple of holes through the eps to allow for expansion of the foam .
I could then shape the board down to the ribs & get the right shape for the board .
Ive never made a board before & its the shaping that I'm worried about but I do have a scrolling saw that I can cut the ribs out perfectly with & I just scored a vacuum pump today & I sort of came up with this idea plus I get the foam for free .
Maybe just as a beginner guide to shaping a blank .
I realise it would add a bit of weight but if you used balsa wood for example & the rib was say only 20 mm thickness on the cross section & say 5 mm thick .
I think you would be able to cut ribs out of the centre of the timber as well so not using as much timber .
Make a stringer to mount all the ribs on & block out the voids & then sandwich it & glass.
It's probably a stupid idea but I had it & just thought I would pose it to people far more knowledgeable than me & see what they think .

Worth a try. Even if it fails it would be a fun project

IMO too heavy

so what density is the foam?? I tend to agree with force10 it's probably going to be heavy. I'd leave the timber out.

I have absolutely no idea of what the density is .
Is there a way to test it ?

Yeah would be way too heavy...... but if it is free then just do it I say :) but no wood
If it is anywhere from 13kgm3 to 19kg/m3 then its usable.
Just weigh a piece and figure out its volume....... your pieces are one eighth of a cubic metre, so if a piece weighed 2kg it would be perfect board building density.

Glue together with Tarzan's grip polyurethane glue, build a hotwire to cut rocker and go shape. If you stuff it up,you've lost very little :)
Just be cautious of too much glue - you don't want hard lines running thru your blank as they will not shape as easily and give u high spots.

BTW I have been looking for source of free styro packing and there was talk of some industries throwing away stuff that is suitable for us so what is your workplace?

Cut a piece 10cm cubed and weigh it, if you don't have sensitive scales, cut a bigger block.
Boards are normally made from 13 or 16kg/m3 depending on how light or strong they need to be.
The heavier foam is easier to shape.
That's another thing, varying densities are a pain to shape. Like wood and foam, foam doesn't cut real well it's better being abraded, especially as you get close to the finished shape. This will leave the timber sticking up, so it has to be carefully cut back to the foam surface. If you aren't careful you can tear the foam or pull beads loose.

It's a clever idea but to be honest I think it's over complicating it, especially if it's your first board.
What Decrepit is saying is also correct, it's tricky shaping a softer surface to a harder surface.
I think you'd be better off spending the time to make some good templates and shaping it from a single block.
Take your time and stick to your original measurements and you should be able to come up with something pretty good first go.
The only way to learn it is to do it. Get into it and have some fun with it!

Good luck, Hoops

Tricky is an understatement too/........

Well the idea was the timber would be cut to the finished shape & they would be me templates to sand down to .
I do also get sheets of eps 50mm x 1000mm x 4000mm so would probably be better off laminating those sheets together .
Ill have to weigh up some & work out density .
Im just inspired by the great works I see you guys posting

^^^ If you cut timber ribs and have a bit of EPS in between each, then sand down - you will still get more EPS removed and end up with something that looks like a supermodel's ribcage no matter how you do it. Real PITA

If you have 4000x1000x50 in anything from 13kg to 30kg and its getting chucked, there will be many of us interested........

Well the idea was the timber would be cut to the finished shape & they would be me templates to sand down to .
I do also get sheets of eps 50mm x 1000mm x 4000mm so would probably be better off laminating those sheets together .
Ill have to weigh up some & work out density .
Im just inspired by the great works I see you guys posting

I also wanted to try ribs like the aeromodellers but like mark says..... its gonna be bumpy and uneven.

Watch Rob Rocks videos, he has a great way of using foam blocks to shape his blanks. Links below.....

My advice is to just learn the proper way. Don't reinvent the wheel! There are others that have tried it before you.
Accept the fact that the first 1 or 2 you do might be pigs. It's a learning process. If you don't go through it you'll never be able to do it.
shaping is one of those things where you never stop learning.
Its good fun, get into it!!

/\/\/\/\ This exactly.

Ok thanks people .
I appreciate all the advice .
I wont waste my time & efforts trying to reinvent the wheel.

But give it a go , it is a lot of fun . If you copy a board or only slightly change it , using templates , the shape should work. Take your time and only three beers max at any time
Plenty of people here to help step by step , post photos and it will inspire others to do the same.
But it wont be cheap. Same kind of cost as a really good second hand board.

Thanks Dar I was under the impression that I couldn't glue under density block's together from year's ago post massive problems with glue cutting with hot wire & shaping sanding .
It's what prompted the rib construction & inbuilt template.
Its just so cool too be able to ask from expert's .