making a plug for a vacuum formed Hydro cowl

[JimClark]

I need to make a cowl for my 1/16th Scale hydro project as the ones I have are for a larger boat than I am making. Plan is to make a wood plug then use the plug for vacuum forming. I am open to making a one off cowl but it has to look good and smooth. My only experience is shaping balsa would like to try carving in Bass wood or something else anyone have ideas tips or tricks?

Jim

[JimClark]

Here is one I made a while ago for the Miss K+ out of Balsa

but this one is shaped like this

[Shooter]

Wow Jim. That balsa cowl looks great. I do a lot of vacuum forming, but it's mostly with ultracal plugs. It's a very strong plaster material that holds up to multiple pulls. One idea would be to shape it out of balsa, then make a negative shell mold so you can pour in ultracal and make a hard positive. Hopefully others will chime in. I'm very interested in this as well.

[RayR]

I am interested in this process as well.

[JimClark]

Shooter more info on the negative shell, what would be used



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[darryl whitman]

thats cool Jim , I have used pine wood to carve, then I put sanding sealer on it. then buff it with car wax.
then I make box around the plug an fill it with concrete. pull the plug out , clean and spray ( Brownells acra-release )
I use it for inlaying rifles barrels into stocks with resin. back to the mold, once sprayed I start laying in fiber glass, 2 to 3 layers after harded pull out the cowl . it works for me .

[CornelP]

The best material you can use is actually a high density polyurethane foam:

http://www.modulor.de/en/Model-Making/Panel-Materials-without-Texture/PUR-Rigid-Foam-Modelling-Panels/SikaBlock-PUR-modelling-board-M650-580-kg.html

This is made by Sika, but I am sure you can find an equivalent. It is very easy to cut, shape, sand, it is widely used for 3d cnc routers.

[Jr Branham]

DSCN1458.JPG

[Jr Branham]

Jim,
If you carve one out of balsa and seal it with epoxy you might can get a single pull of plastic off it. Then support the plastic and pour molding plaster or hydro-cal, ultra cal, etc in that pulled plastic. That will be your male mold. The higher quality components allow you to make more pulls. How many cowls are you tryi ng to pull?

[JimClark]

Only one or two

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[Jr Branham]

In the pic of the miss K cowl, that would not pull as pictured. The huge forces (vacuum)would break the sides of the driver compartment due to the arch on the bottom, You could build that area up with bondo.

[JimClark]

That actually was only the first step. The final was a different material

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[Jr Branham]

If you build the male molds (not balsa), I will pull you a couple. My machine has a surface of 2 feet by 3 feet. I could pull several in one sheet. I have .040 styrene. I do not have any abs.

[JimClark]

I have a lot to think about on this this is a whole bunch of work I didn't really want to do

[RandyatBBY]

I like to use press board or composition board. I have several thickness of board I cut it a little small and use bondo to finish. I have made hundreds of mold over the years I probably have what you need and can form it out of Stryene. I have made several shovels that I did not release because I felt pickles were better for my business. I have a Micro that you know of, I also have a 21 inch, a 23, a 34 and a 36 in process.