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Joev259A

material for making a master mold for scratch building

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G'day. I'm making a master for vacuumforming a fuselage. In the past I used Bondo two part putty (automobile stuff), which sets up quickly and is solid enough to take the vacuum form. However, once it sets it is VERY difficult to sand quickly, and dust is everywhere. I've tried regular (grey) modeling clay, but I don't think it will keep its form before crumbling. I was thinking of Skulpy, but that's about $50.00 a container (the fuselage is 14 inches long, about 3 inches high and 1 1/4 inch deep). Does anyone have suggestions? I was thinking of Plaster of Paris. Don't recommend the "take a block of wood and whittle . . ." route-- wood does not like me. Thanks~!

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Hey Joe.....where ya goin' with that model in yer hand......(sorry, too easy to pass up!) :smiley4:

 

Although I haven't used it myself, there is this stuff called RenShape foamboard, which I've seen a lot of scratch builders rave about. Here's a link to one manufacturer: http://www.freemansupply.com/RenShapeModelingan.htm You can also Google Ren Shape and go from there.....

 

Supposedly its available in all sizes, including blocks big enough for fuselages, sands and carves like balsa but has no grain to fill, and leaves less residue too. You'll have to see how expensive it is, but if you hate balsa and bass wood, this might be an alternative.

 

Outside of that, there are plenty of epoxy putties that are clay-like when first mixed and dry rock hard. Plumbers epoxy, pool repair epoxy, and marine repair epoxy are all available at hardware and department stores. Miliputt is another possibility, although as a hobby putty it's more expensive for the same amount. If you use these, I strongly suggest you make your fuselage master up with a lot of plastic stringers and bulkheads, and then fill between all of those with sheet plastic to a point JUST below the "skin". That way, you can smear the epoxy putty on like the skin, but slightly thicker, and then sand back down to the outline of your bulkheads and formers. In fact many of them can be shaped and smoothed with a finger and alcohol until they set up, which can cut down on the sanding needed.

 

I'm sure there are other ideas, but until they show up, I hope this helps! Best of luck!

 

GIL :smiley16:

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Thanks for the information. I think the Milliput will be too expensive-- the others I'll look into. I remember Dr. Frank Mitchell using that surfboard material for some of his stuff. I'm aware of the bulkhead techniques-- I wrote a couple of articles for the Journal-- one on scratchbuiding an AH-56 Cheyenne (all Bondo) and the other a 1/48 scale HU-16 Albatross. Stay tuned . . .

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Why wouldn't you simply carve the male molds from balsa? It is not too expensive, it is easily available and it is easy to carve. I have used this method many times to create a male mold for vacu-forming. Regards, Nick Filippone

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thanks- wood and I just don't get along.

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For additional information on Scratchbuilding, refer to Shiffer Books' "The Master Scratch Builders" by John Alcorn. It is an excellent reference book on the subject. Happy Modeling,

 

 

 

Mark Fiedler (aAzZ09)

IPMS#14333

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Thanks- I have both books. great!!

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thanks- wood and I just don't get along.

 

I have the same relationship with paint :)

 

Just wondering if you've tried using basswood and shaping it with sandpaper (the real 150-200 grit stuff meant for woodworking). A 1 inch wide x 11 inch long strip of sand-paper used like a giant flexifile works great to create curved surfaces. The basswood works a lot faster/easier than even white-pine and is sturdier than balsa - its a lot more like fine-grain styrofoam than wood.

 

 

If you've already tried basswood, then never mind...

 

Don

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Don, I have also used basswood. It is indeed sturdier and will "hold an edge" better than balsa because it is harder. But I always found it took longer to sand to shape because it is more dense. I usually use balsa for male molds, being somewhat lazy and impatient myself. Nick

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If you have r/c model sailboaters in your area check with them. Those guys often build their own boats to standard class plans, and make a master mold (male)building up layers of fiberglass in hull construction.

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