Different materials used for making molds

[ozz]

So, I was wondering what materials everyone prefers to use to make a buck or to sculpt with to make a buck.

I have tried a few things. I used to work in the molding and casting department for a Dinosaur museum. We used just about everything, and depending on how big the project was for us to make, we used different materials. If the project was big, we used plaster. If it was smaller, we used Bondo, and two part plastic to make the base. We rarely used clay because of the molding and casting process we used. We used the two part foam sometimes as well for really difficult projects that were big and needed a "filler" base.

I am starting to make some casts for Star Wars armor, and helmets. I recently used (just) plaster to carve a full set of clone armor. I decided to do this because of the size, and the plaster stays workable for a few days, as long as it's thick enough, and can be sanded and smoothed out nicely while it is still wet. I am not sure if it will be able to take the vac form process well. I am guessing the heat will destroy the molds/bucks I made in a pull or two.

I even tried to do a plaster base and Bondo on top, but the Bondo keeps the plaster from curing correctly, and makes it a little hard to form (the Bondo) correctly.

Now that I am starting to try to do helmets, I have seen a few ways people have done this foam carving process. I decided on trying the foam back/base carved out into the general shape, and Bondo to cover. I have foam residue everywhere, and it is making the biggest mess. Plaster made a mess, but I just wiped it up with a wet towel, The foam is way worse. lol Like I said: I have rarely used clay for this kind of project.

So, I wanted to know, for the helmet/prop makers out there, what materials/process do you find easiest to make these type of sculpts?

 

[ozz]

Guess I a question about some trade secrets... lol

Here is a link to one of the sculpts I did with all of these bases. http://www.rmdrc.com/archives/2662/dromeosaurus-plaque_black

It had a foam base, plaster "rock" over the top (which I had to carve to look natural) and the bones are the 2 part plastic.

I see this topic has over a hundred and twenty five views, but no one wants to comment.... Is this thattouchy of a subject no one wants to answer? I will even take a PM.

 

[sbaxter]

Guess I a question about some trade secrets… lol

Same thing happens to me on most model forums a fairly high percentage of the time. I learn loads just reading threads, but when I post a specific question, I often seem to stump the experts. Not to say the experts aren't experts; I just have a knack for posing difficult questions, I suppose. Maybe I just want to do crazy things sometimes that cannot be done!

I can't help you with this question here, but I'm interested in any answers you might get.

Qapla'

SSB

 

[ozz]

Well, I found out an answer to one of my concerns:

Brushable Shore 25A Hardness Platinum Silicone Rubber Compound.
1A:1B Mix Ratio - No Scale Required.
Note: This product will not work with modeling clays containing sulfur under any circumstances.

MIX RATIO: 1A:1B by weight or volume;
POT LIFE: 50 mins; CURE TIME: 4 hrs; SHORE HARDNESS: 15A; COLOR: Green
Note: This product will not work with modeling clays containing sulfur under any circumstances.

Smooth-on will not work with clays. So, DO NOT make your vac-formed bucks/molds out of clay!! Or at least clay with sulfur...

 

[robn1]

I haven't made a helmet, or anything quite that large. But if I do I'd use Bondo over foam if it's something smooth and simple, or sculpt in clay if it needs more detail.

Plaster is fine for vac bucks, I've used it with no problems. Durham's Rock Hard Water Putty is also good, I like it because it's tougher that plaster.

Platinum silicone can be used with non-sulfur clay, but it has problems with other materials too. I like to paint my master parts with Tamiya spray paint which inhibits platinum silicone. I like Smooth-Sil 945 for it's 1-1 mix and 6 hour cure, but it takes 72 hours to cure against Tamiya spray. I've been using tin silicones with fewer problems.

 

[ozz]

Thanks for the reply Robn. I was hoping the plaster would hold up for a few pulls...

Never thought of the water putty.

It looks like I will have to shop around. Smooth-on isn't the only place to go...

 

[stormtrooperguy]

I LOVE sharing trade secrets!

My go-to materials are:
Smooth-On Rebound 25 silicone
Smooth-On Free Form Air for the shell (more later)
Smooth-On MoldStar Fast silicone

Both are platinum cure silicones with a long library life (how long they'll last before naturally decaying) and capable of a lot of pulls (I've had molds that have gotten 50 - 60 helmets before they start to fail)

Rebound is a brush on, so it's good for big stuff. It takes a long time to build up the layers, but it ends up using the least possible amount of silicone. I brush up 5-6 layers of it on a helmet and that's usually good.

The silicone is a relatively thin and floppy thing though, so you need a solid shell to support it while casting. I use Free Form Air for the shell. I used to use their Plastipaste product, but the Air is lighter and easier to work with.

For smaller molds I love the MoldStar Fast. In half a day you can pour a 2 part box mold and start casting.

I've got a bunch of videos in youtube that might help:
https://www.youtube.com/playlist?list=PLJWVKaDzrhxreUpOPKMmK4vuu0_esNqvs

 

[ozz]

Nice! Thanks for that response Stormtrooperguy!

I was thinking the smooth on 25 (orange) was my one to go for. But the shell, how does it compare to the plasti-coat? Which one would be easier? And Plasti-coat I or II?

How about roto cast? I will be doing it by hand and without a machine. So what would work best? I have seen the smooth cast 300, but I think it only is wet for 2.5 seconds. And the 305 is 7? But I saw that 65D will last for 7-9. That might be a long time, but it might be long enough to cover on the first coat... maybe?

 

[ozz]

Here's what I have so far:

Clonetrooper armor bucks made out of plaster. Mostly Finished. (Needs some re-thinking to fix under cuts and ends for vac-form release.)
Clonetrooper helmet started, foam/plaster base, will have Bondo shell.
Stormtrooper armor started. I have made one out of plaster base, Bondo shell.
Stormtrooper helmet started, foam base, Bondo shell. (I think I used the wrong foam, but it works good enough.)

I will start a WIP thread some day...

 

[NormanF]

Nice! Thanks for that response Stormtrooperguy!

I was thinking the smooth on 25 (orange) was my one to go for. But the shell, how does it compare to the plasti-coat? Which one would be easier? And Plasti-coat I or II?

How about roto cast? I will be doing it by hand and without a machine. So what would work best? I have seen the smooth cast 300, but I think it only is wet for 2.5 seconds. And the 305 is 7? But I saw that 65D will last for 7-9. That might be a long time, but it might be long enough to cover on the first coat... maybe?

I meant to respond to this yesterday. I use 65D. You really should do a few thin layers even though your back will be sore after the first one or two. Otherwise you will end up with what looks like a thick line of plastic on the inside of your casting when the resin suddenly sets.

Here is a good demo, and what pushed me over the edge and convinced me I could do this stuff. I figured if he can do it drunk then surely I can do it sober

 

[ozz]

Haha, maybe you have to be drunk to do it...

- - - Updated - - -

And I found this so my arms won't get tired... http://www.instructables.com/id/Make-A-Rotational-Casting-Machine--For-Under-150/

 

[robn1]

Here's one that looks very easy to build.

 

[Duncanator]

I was confused by the first posting whether you were looking for info on sculpting a pattern, or molding it or vacuforming it.

I like sculpting large patterns with 4-6 pound urethane foam. It is rigid and sands quickly. I can often get it to 95% or closer to my final desired shape, then I vacuform a thick layer of styrene (.060-.080") over it. I leave the foam in the vacuform shell, and then use bondo to fill and smooth it to the final finish. After that, I can mold it or vacuform over it. It won't be the most durable vacuform plug, but with powdered talc and some care you can get several pulls with no troubles. Perfect if you just need a few parts.

 

[ozz]

I was confused by the first posting whether you were looking for info on sculpting a pattern, or molding it or vacuforming it.
QUOTE]

Actually, a little of everything... lol
As Joe Dirt said: "I'm new, I don't know what to do!"

I also wanted to see if anyone else has used plaster to vacform with. Since I am very new to vac forming, I wanted to know if my buck/molds would stand up to the process. Or if I need to add bondo to it to make them last longer. Or if I should just start over with an "easier" process, and/or materials, and which ones would last longer...

You know, the usual...

 

[Duncanator]

Plaster works great as a vacuform pattern. You just need to make sure it is thick enough or reinforced to take the pressure. The vacuum in vacuforming just removes the air beneath the warmed plastic, which allows the atmospheric pressure of the surrounding air to press the plastic down on your pattern. Atmospheric pressure at sea level is roughly 15 pounds per square inch; so if you have a small pattern, there isn't much force exerted on it. A large pattern has to withstand more pressure because it has more surface area, and every square inch is being pushed on by 15 pounds of air in the vacuforming process.

You have to be careful when using dissimilar materials in a vacuform pattern, because the bond between each material is a potential failure point. Some materials bond very well to each other, but others (like plaster and bondo) don't bond to each other well. I also like to have my materials to be of similar hardness when shaping them. That way when I sand them, I'm not removing a lot from the soft areas and just a little from the hard areas. It turns out lumpy.