Doug Conn wrote:
> Oh ! I see now. Ron, is this what you were describing, too ? Sorry, I
> misunderstood. I guess it would be like this, then, where I sand away
> the blue areas
Yes, grasshopper - the pebble is getting closer.
> What material is a good choice ? I don’t think foam would work for
> vacuforming. Even I use fiberglass, I’d like a mold that survives more
> than one use.
By far, the best choice is .... wait for it .... you'd never guess it on
your own .... but the winner .... and all around best choice is:
Cedar Fence Boards
Cedar is relatively cheap, cuts and sand easily, the dust does not fly
in the air (it actually freshens the air in the workshop) and accepts
any filler and sealer you want to use. Cedar is very light when
compared to other common woods and it forms a very smooth surface when
sanded, even across the grain. Unlike balsa (which is also much more
expensive), the sawdust drops to the floor instead of floating in the
air. In fact, if you sweep up the sawdust and put it in a plastic
container, you can mix it into any resin as a thickening agent to make a
nice sandable putty (it's called "wood flour" when used like that). So,
after shaping the plug, you mix some epoxy or polyester resin, throw in
enough cedar dust to make a "mayonnaise" consistency and then smear that
over the surface. When dried, you can sand that just like wood filler
and finish the surface as smooth as you want.
I've personally made two large scale sailboats using cedar:
http://www.pittelli.com/schooner/photos/ships/Frank/Wasa/
http://www.pittelli.com/schooner/photos/ships/Frank/Junk/
and I've found it to be the best softwood to work with for
non-structural components. (Popular is my favorite choice when a
hardwood is needed for strength or durability.)
Styrofoam is a workshop nightmare, especially in the winter when static
electricity will cause it to stick to everything. Unless you have the
right tools, it is harder to work with than wood and less forgiving. You
cannot make a sharp angle or detail in styrofoam like you can in wood.
Worst, when you push on it, it compresses and then rebounds, making it
very difficult to get a smooth contour. We (not just me) tried using it
for numerous large scale boat molds in the early warship days, learning
with each bad project that wood was the proper plug-making material.
Frank P.
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