Torso Casting as a Patterning Aid

[besserai]

Patterning is difficult to do on your self since you can't see everything and only have two hands. So I have decided to make a casting of my self as an aid. I plan to make a single cast of my head down to about mid torso including my arms down to the elbows. This should enable me to do some patterning on the head, neck, and shoulders (places I find especially difficult to do on myself).

I've been reading around mostly here: http://www.smooth-on.com/

My plan:

- Wrap gypsona plaster bandages alone on the head and upper torso
- Cut down sides and up armpits
- Seal two halves togeather using more bandages
- Fill the mold with a castable rigid urethane foam like this: http://www.smooth-on.com/Rigid-and-Flex ... catdepth=1
- Break of the plaster and done.

I have two questions for you all:

- Most places I read talk about alginate and other compounds for casting but I am not sure this is necessarily needed since those seem to be meant for capturing fine details which I don't need. Can my plan of just using the plaster bandages work and skipping the alginate?
- What do you think of the rigid urethane foams? My budget is 200 or so dollars and I quickly learned that resins are kind of expensive for the size of the project i'm doing (probably more than 5 gal). Also expensive considering that I might mess this up.

Thanks

[wcallen]

The answer always depends on how detailed you need things to be and how you like working.

I have done a cast with "cast" plaster bandage material and I got something that seemed reasonable to me. Since then I have seen some built with the fiber glass cast bandages that seems better. You can get a more durable result in a pretty thin layer. It is more expensive, but you don't end up with chalk as you play with it.

For things like heads and bodies where you will either be adding padding or clothing, either should work.

I think the fiber glass bandages are more expensive but probably work better in the long run. You can reinforce them all you want with more fiberglass and make yourself a dummy if you want to.

Wade

[Chris Gilman]

If you'd like I can give you some pointers on how to do this, but it's too complex to describe here. If you’re interested call me at my shop any week day and I'll talk you through it.
(Edit: I see by your posts you may be new here. This type of thing I do for a living so I have about 25 years experiance, I can be reached through www.globaleffects.com)

[besserai]

I am going to take you up on that offer right now.

[Gurahl]

Argh! And the Wizard disappears behind the curtain again..

[coreythompsonhm]

I've been wanting to do this too, only a full body casting.

[besserai]

I had a lengthy conversation with Chris on the phone and he convinced me that a full body casting is not worth the effort for a patterning aid. (I originally thought I wanted one too...)

Beyond just difficulty in creating the casting the final result is not worth it. His reasoning was that you don't need to have the head there when you are trying to pattern for the feet. If you want to see the whole suit together as a whole just get an armour stand.

It is useful to have adjacent body parts on a single casting though. For example it is useful to cast your neck and head together as one so that you can see the gorget and the helmet at once.

I am going to attempt to use the techniques described by Chris and post the results here to spread the knowledge a bit. Its going to take me a week or two to gather the supplies needed. If I fail miserably there have been some simpler techniques described to me which I will employ instead.

[coreythompsonhm]

Thats a very good point, and makes things soooo much easier logistically. What products are you going to use?

[besserai]

The supplies that I am going to use (all recommended by Chris)

For creating the mold:
- Plaster Bandages: http://orthotape.com/plaster_bandages.asp
- Vaseline: Release agent, so the plaster doesn't stick where I don't want it too.
- Saran Wrap: So it doesn't stick to my hair.

For creating the positive:
- Bondo thinned with a polyester resin: For creating a hard shell.
- Johnson paste wax: So the Bondo doesn't stick to the plaster.
- Rigid Urethane Foam (specifically the 3lb/ft3): http://www.smooth-on.com/Rigid-and-Flex ... index.html

I am going to detail all of the steps once I get started but I'll give the basics as I understand them.

The mold is going to be made in two halves. The seems will run along the top of the shoulders and from the armpit to the hip. Make the back half first and overlap the seem by about an inch. Let it dry a bit. Spread vaseline on the front and over the back plaster half a few inches. This will allow the front and back to overlap and lock together but they wont stick to each other. Make the front half overlapping the back half but only over the vaseline areas (so you can remove it). Wait until dry and then remove.

You now have a mold

Casting starts with masking tape holding the two halves together. Liberally paint the paste wax on the inside of the mold and let dry. Mix the Bondo up so that it is thin enough and paint it on the inside of the mold. Mix the two foam components well and pour into mold. The foam will go through three stages foamy->rubbery->hard. Only add more foam once the foam reaches the rubbery stage. This should take up to five minutes but this depends on environmental factors. Cut masking tape.

Now you have a positive.

[Chris Gilman]

Sounds good. Remember to practice on a mellon or something simple. You will use a small amount of material, but you will learn alot and save risking the material you want to use on the body.

[coreythompsonhm]

Well my question is, why thin out the bondo?

[besserai]

Chris actually explained that to me as well and as far as I understand it is to allow a more even coat. Basically you want to be able to drip a smooth coating down the side of the mold.

Bondo is naturally very tacky and it will be difficult to do this straight out of the can.

I've found polyester resins online for about 15USD per pint. This is a lot and he said you could use just a couple of ounces though.

He got technical and I am still working on understanding some of the physics behind this property.

[Chris Gilman]

Thixotropic is the word I used. ( http://en.wikipedia.org/wiki/Thixotropy ) I have found with a foam bodycast that it is easy to “chew” up the raw foam while working with the finished casting. So as a skin for the foam, I use Bondo that has been thinned out with polyester resin to allow you to paint a layer in the mold. (about 1/16th to 1/8th inch) Changing the amount of resin added changes the thixotropic quality of the Bondo. So when the 2 halves of the mold are open, you can paint in a layer with a wide disposable brush, within ½” of the seam. Then while the Bondo is still a little “green” (flexible) you fit the 2 halves of the mold and tape them together. Now with another thicker batch of Bondo/resin, you can pour this thicker mixture down the seams to join the front and back. Now when you add your rigid foam, the foam will stick very well to the Bondo/ resin coating and give the bodycast a durable skin.
The most durable way we use is to fiberglass the inside of the mold, but if you want to sand the casting smooth, then the Bondo/resin thicker “gelcoat” gives you a great surface to do this.
The problem, for armour, is your real body is “squishy” and a bodycast like this is not. So if you make a cuirass using a cast like this, you want to carve away material between the ribs and hips and replace this with soft foam so when you make the cuirass, it can come in at the waist the way real armour does. You just have to estimate how much your body compresses.
The other thing to keep in mind, is all these materials shrink a little (about 2% to 4%) and you are going to have an akaton on under the armour. so adjust accordingly.

[coreythompsonhm]

Interesting, William Hurt and I were talking about that same squish factor a few years ago, trying to figure out a torso cast that would allow for this same squish. I like your solution for that problem!

[besserai]

I am trying to find the polyester resin locally and nobody around me stocks a product by that name.

I have however found a "fiberglass resin" that some people on the internets think works just as well for thinning bondo filler. Does this make sense to people here? I am going to try this out first to see if it works. If not then ill buy the actually polyester stuff.

[coreythompsonhm]

I believe polyester resin or epoxy resin is used for bonding layers of the fiberglass fabric together, then a gel coat levels and seals the surface. Be careful with what they are calling "fiberglass resin" could be the epoxy stuff, it should say on the can. Any auto paint supply store should have fiberglass supplies. I know i'll be looking at wesco up here in Seattle.

But dont quote me on that, I may be wrong.

[Chris Gilman]

"Fiberglas resin" is almost always Polyester resin. Epoxy resin is usually identified as Epoxy because it is more expensive. Having done this type of thing for so many years, I forget that items may be labeled as "Products" instead of as "Materials".
As for FRP or fiberglass reinforced plastic.
Here is an excerpt from my propmaking skills book I’m working on:

… Most common is “fiberglass” more correctly, “Fiberglass reinforced plastic” , “Fiber-reinforced polymer” or “FRP” However this term is misleading as it is really “Fiberglass ridgidized with plastic” It is the glass fibers that make FRP strong, not the plastic. Fiberglass comes in a number of ways, cloth, matt, roving.


...Polyester resin and epoxy resin are the most common for use with fiberglass and along with the family of urethane resins can also be used for casting parts. Polyester resin is the most common for fiberglass (FRP) work and are generally weaker than Epoxies. Like other plastics, these are formulated for specific application. (The specifics of these will be covered in the chapter on composites) This includes the addition of a variety of fillers, such as micro balloons (microscopic hollow glass spheres) to thicken polyester into the plastic body filler commonly called by the trade name Bondo. Epoxies are also available in a wide range of formulations. Epoxies are most common as glue, you most likely know them as “5 minute” epoxy. But epoxy is used in many different forms of plastic part manufacture. Including of course for composites (fiberglass, carbon fiber, see below) and are stronger, but more expensive than polyester. Epoxy can also be mixed with micro balloons and made into a material know in our industry as syntactic dough. This is great for making durable structures or sculptures that are exposed to the elements. Disney uses this for many of its amusement park installations because of it durability and strength even when exposed to severe weather and sun....

Polyester resin FRP is usually done in three steps. Gel-coat, laminating, finish coat. The Gel coat is the surface you will be seeing in the finished product, so this is applied to the mold surface as the first coat. It is formulated to set up a little harder than the other resins and often has“filler” added to give it a better thixotropic quality so it will “hang” on the mold surface, resulting on a slightly thicker coating. Laminating resin is used, as the name implies, for laminating. Once cured (hardened) it stays slightly tacky, so subsequent layers will bond to it. Then a finishing resin is used for the last layer of glass. This resin has wax in it, so the final coat will be smooth and tack free. Fiberglass does not like to make sharp bends, so while laminating with it, it is necessary to fill in “rugged” detail or tight inside corners with a thickened polyester resin. This is done by adding chopped fiberglass, or micro balloons to the laminating resin to form a paste. This is then activated with MEKP just like you normal polyester resin and spatula this filler into these corners. Make sure the finished surface is smooth and lump free. You want your glass layers to lay down nicely and if you leave lumps in this filler process the glass will not lay down smoothly and air bubble can get trapped making the lamination very weak in the areas.

[besserai]

My plaster arrived and I got straight to work.

First working with my plaster buddy to practice on the watermelon.




I had plently of plaster so we decided to go ahead with the torso casting too.




I learned a whole bunch and made a bunch of mistakes. I will detail all of my lessons some other time when its not 2am.

[Chris Gilman]

Looks good.

[Ugo]

Go to Fiberlay off hwy 30, They stock everything from molding supplies to casting urethanes, expanding foam, fiberglass, resins, epoxys, etc

[besserai]

I finished doing the torso casting and it worked out very well.

Chris, thanks for all the help it turned out to be very useful.

Ugo, I'll try that place out thanks for the recommendation.

It turned out a bit lumpy but that is to be expected from using paster:


Here is a picture of me using the casting to pattern a new gambeson:

[Michael Cartwright]

That's bloody interesting stuff, thank you!