laminating paper from a mold

[stone]

My first design in paper was an L-19, but I found that the engine cowling didn't look very realistic. I made a cowling in plasticine and cast it in dental tech.
plaster. I plan to laminate this inside mold, using glue-soaked newsprint or thin paperstrips. What would be the best and simplest seperating agent, barring vaseline, which I wouldn't use for obvioeus reasons ?
Any one please ?
Serge

[dansls1]

I'm sorry I can't help, but if I had gone through the trouble to make a mold like that, I'd probably be looking at doing one of the simple plastic vacu-forming techniques using plastic like people do with canopies and then painting it.

[stone]

It didn't take very long Dan, modelling in plasticine with a fairly simple shape takes only some 20 minutes. I poured the plaster in 10 or so,then set it aside to harden. Taking the plasticine out,again no more than 10. And consider this: You'll end up with a paper cowling ! Not plastic !
Serge

[Leif Ohlsson]

I agree, Serge, paper is nice. But how shall you be able to avoid painting, if you sort of make up a papier mache cowling?

I hope Gil Russell bites on this one; he's been there, I know.

See this post at Kartonbau.de and following.

Leif

PS. A few post down from that in the same thread there is a useful collation of articles on the theme "Designing paper models without CAD", which ought to be right up your alley, Serge!

[stone]

Leif,
the Fury build, was the one I told you about. The old fashioned way he uses,I copied for theL-19. After a laminated nosesection is done, you could als"plank it" in precoloured paper as done by Gil. Petal glueing over an existing shape would be les tricky then normal as you could fairly easily adjust the pattern, even by trial and error.
As to cone construction, there is also a good tutorial on :sheetmetal world.com and a Navy piece, the sitename of which escapes me at the moment.
Serge

[stone]

After answering yours on the problem of working with unprinted papier machee, I had a look at your link about the DH 88 and I was completely astounded. How on earth you do it is beyond me. Absolutely top flight, my sincere respects.
Serge
P.s. I discovered a cone calculating site at ShroudCalc 2.2

[SCEtoAUX]

I have seen candy makers use corn starch as a mold release for candy like gummi bears. Maybe it would work for your application too. If you can not find corn starch maybe talcum powder or baby powder or even rosin like baseball pitchers use would work.

The baby powder would make it smell good, too.:D

[Gil]

Hi Serge,

Attempting the next level in realism with the paper medium opens a wide avenue for experimentation. It's reassuring to see that you're venturing outside the comfort zone.

Modeling with plasticine is an excellent method. Especially when the clay can be abutted up against a former. A very clean, closely toleranced mold plug can be realized with this method.

The dental plaster mold looks clean and ready for layup. A couple of points which serve as an answer to your original request for a good mold release agent.

If you use paper that is water saturated no mold release is required. The plaster will aid in absorbing water from the paper. The paper shrinks as it dries naturally separating from the mold. This is by far the least complicated method.

Adding starch, PVA or other papier mache binders complicates the situation and will require a separating agent. Sealing the porous structure of the plaster "de-tooths" the surface so that the mold release agent can be effective. I suggest Krylon Crystal Clear for this. The plaster will absorb the first coats but will start to gloss by the third or fourth. A simple mold release consists of mixing Vaseline thinned with paint thinner. It can be brushed on and allowed to dry.

I've used a number of different "binders" for paper layups. The method I like best is the water only layup method. The piece is allowed to thoroughly dry then trimmed in the mold before extraction. The piece is then painted with nitrate lacquer or lacquer sanding sealer to strengthen and seal the surface. It also waterproofs the piece.

I sometimes use Hard Acrylic Modeling Paste on the inside of the piece which doesn't require sealing with lacquer. The paste is thinned with water and brushed onto the internal surface of the molded piece (dried, parted, and reinserted into the mold). PVA can also be used in the same way. Be careful to insure that the piece doesn't become attached to the mold by over brushing the binder into the paper.

The piece is now ready to paint which, often, proves to be more difficult than making a molded piece (i.e. paint matching).

The nice thing about a mold is that if you're careful you can always make another one if the current version doesn't live up to expectations.

Best regards,
+Gil Russell

[stone]

Hello Gil,
Thank you for your extremely helpful and concise advice. I didn't dream up this plasticine operation myself, but we used it in Highschool to make masks.In the early sixties I bought a small book by Ron Moulton of MAP publications on building flying scale models.
As this was at a time when Vacu forming was still very seldom used and extrusion not for the "hoi polloi", it also contains a piece on paper laminating( see attachment). Its main use seemed to be for wheels and spinners.Having designed and "white built" my
first plane I wanted a more streamlined cowling, so then I remembered Ron Moulton's
article. He used to be editor in chief of Aeromodeller Magazine.By the way, how would you go about designing (by hand ) a rounded- off shape? For instance a wingtip or the nose piece of a Cessna, one with a fairly flat front. I have seen all these little cuts around the edges, is there a simple formula for this ? Again my thanks
Best regards
Serge

[Don Boose]

This is the kind of discussion that makes membership in this forum worthwhile. The quality (and courtesy) of the discussion, the standard of craftsmanship, and the ingenuity are all wonderful.

When Bill Geoghegan and I were in high school back in the 50s, one of the subjects we studied at the Baltimore Polytechnic Institute was green sand casting from wooden patterns. As I recall, the mold release was walnut shells ground finer than talcum powder and shaken through a porous little cloth bag. I presume this material is still available, but I do not know if it would have any advantage over corn starch.

Don