building a female mold from scratch (without a male plug)

Thanks mate!

 

Something like that ?

http://www.3dwsystem.it./gallery/barche-a-vela/36-regata.html
http://www.3dwsystem.it./images/gallery/vela/36_regata/foto__22_18.jpg

Seems that they use section spacing closer than 500mm. I would say more something like 300mm (1 feet)

 

Wow theres some pretty cool stuff in that sight !! and nice finish !! lots work !! but use the right products it shows what you can exspect if you put in the work !!
Great stuff Going to hang onto that site !!

 

Some great stuff Tunnos, I like to apply the principle of "who ever applies the filler sands the filler"= application techniques improve rapidly. Some thing else is I usually put a couple of wraps of tape around the ends of the board, then there's no corners to rub into the surface. Jeff.

 

I would never sand anyone elses fill jobs !! never! . using the steel ruler method some times hardly had to touch the filler just sand so the high build undercoat would adhere properly !.
Used to use auto filler and mix a little acetone with it to thin it down and get a really smooth easy fill with no lumps , acetone evaporates quickly and in thin coats the amount left in the filler after it had been wiped on was almost zero as in nothing !!have done this for more years than i can remember .
NO DONT USE STYRENE it dosent evaporate properly .
I always use acetone in high build paints as well from the time it leaves the end of the gun and hits the surface most has evaperated into the air and if you gently blow air over the surface of the paint its just about completely all gone . Its only used to get the paint to atomizes into smaller drops and get a fine spray !!!.

 

Thanks for your help everyone! that website was great! lots of photos, which always say so much more than words could.

So frame spacing for the mold, 500 mm too far? granted that more frames would be more rigid, but it only has to be strong enough to make the boat, not withstand forces at sea like the hull will.

My main concern with more frames is that a) it will cost more, although in she scheme of things it wont be a huge amount, and b) it will be more work, chamfering edges in order to plank it... also makes it harder to ensure fairness as each frame will have to be angled perfectly, and there are more to do.

On the upside though, it will make a stronger mold. There are always two sides to the story.

 

You can see there another female framing built for foam.

http://forums.sailinganarchy.com/index.php?&showtopic=90914&st=0&p=2462236&

I don't think the close spacing of sections and stringers are for strength, but more for surface precision : less sanding and filling, which is difficult in a concave surface.

I guess there is NO chamfering done on a rather thin plywood. I fear parts are raw from CNC router. And probably a 3 axis only, not a 5 axis that could do chamfers.

Also, in the highly curved parts in the stem, longitudinal stringers are no longer battens, but horizontal sections CNC cut. (visible on others molds from 3dw).

Last, one interesting question : how do they do the mold planking airtight for infusion ? It looks like cold molded, but only one layer.

 

It looks to me like they were planking diagonally, and on top of the stringers rather than the framing, so no chamfering required? On 20mm MDF, you would definitely have to chamfer the edges, i just cant imagine it working if you don't. I think its just a different approach to the same method... Might have to rethink the best solution.

As for surface preparation for infusion, i too would like to know, as i intend to infuse. I am sure that there is a spray on finish that would work, as i have seen it done. Not sure which is the best though. perhaps someone could suggest something?

 

Found this, similar method and quite interesting. For a skiff hull
http://www.rclass.org/info/construction/leech-mkiii/mould-construction