Mould casting

[Jim Hunziker]

Are there any tricks to getting a glass smooth casting? Mine always come out a bit rough. I'm casting into a glass smooth silicone mould. I've tried blending the paper pulp for longer and shorter times, with more and less liquid.

[whulsey]

I would say that it's just the nature of the beast since it is a suspension of particles in a liquid and not a solution of liquid.

[missileer]

Years ago, when I worked with paper sculpting, I would coat the rough form with the same dope that you would use on a paper covered, wooden frame aircraft. Then use 400 grit sandpaper to smooth it somewhat. Then add another coat of dope and this time sand with 600 grit sandpaper. Finally add a third coat and polish with 800 grit sand paper. Hope this helps.

[Gil]

For your two posts;

The Art of Paper Casting for Card Modeling

-Gil

[Monkey]

I once used a thick paste of all purpose flour and water brushed into the mold before I applied the pulp. It sort of works like a gel-coat in fiberglass molding. The result was a very smooth, slightly shiny surface. I also discovered that the addition of the paste between layers and on the back of the final layer almost doubled the hardness and over doubled the strength.

A word of caution though: be careful of your mold material. Plaster of Paris works very well with straight paper pulp, but the flour paste will stick to it like crazy. It will not, however, stick to silicone or plastic molds. At least not in any of the experiments I have conducted over the years.

[Gil]

Monkey,

Applying thin layers of gelcoat (slurry molding) prior to blanketing with paper fiber is a great idea. I've come up with a cardmodeling paste that casts hard with high detail.

Makes for an interesting experiment:

• Take a highly detailed plastic model airplane fuselage and create a female mold from it
• Use several coatings of the cardmodeling paste to create the detailed gelcoat layer on the female mold surface prior to reinforcing it with the paper fiber layer

Will this be far trickier than it sounds or will it be a piece of cake right off the bat (with suitable release agents of course)?...,

-Gil

[Jim Hunziker]

Thank you, Gil, for your instruction sheets on how to do the castings. I'll give them a try.

[whulsey]

Gil, thanks for posting the link to your previous thread. Jim meet Gil, one of our resident wizards of advanced edge paper techniques.

[Monkey]

Gil,

In theory, your idea with the plastic model kit will work. I almost succeeded in doing that very thing. I never could get a suitable mold, but I was limited on what materials I could use for the mold since I didn't have the money for RTV or any of the other professional mold making materials.

If you try it, I would love it if you would share the results, even if it's an epic failure. I always have to tell myself that it is just as important to know what doesn't work as knowing what does. As of now I can consider myself an expert on what doesn't work.

[Gil]

Bill,

Thanks for the brief intro bio. Not as wizardy as I'd like but sometimes you have to wait for those flashes of intuition which can be as rare as the "green flash" from a setting sun.

Jim,

This links to the build of MiG-17 mold build with minimal cost materials. I shy away from RTV unless it's something intended for a prototype pre-production run.

At the time the thought process was to clad the fuselage with rivet detailed aluminum panels made out of 0.005" aluminum tooling foil. The design ended in a sort of designers limbo as I retreated to think out the entire design approach. Yeah, go figure time.

During that period I discovered that aluminum will receive inkjet ink directly if it is first anodized (microscopic holes that hold the ink and is a very durable printing on aluminum method). This led to yet another conundrum - to print or emboss rivet and line detail not to mention access panels. Either way the aluminum panels retain their ability to form the necessary compound curved panels of an airframe.

I have to make up a decision tree to come to some sort of conclusion - but if it doesn't look right it will be back to the drawing board...,

Decisions, decisions...,

-Gil