Making Molds (1 Viewer)

[Big Miller Bro]

I wasnt sure how many other 'drop cast' hobbyists make their own molds but I thought I'd add some info about what I do.

I make my molds out of 2 materials when drop casting metal (or liquid plastic):

The cheapest is Mold Max 30 (by smooth-on) it has a hardness of 40 and I can get around 50 casts off of a well designed mold (no undercuts).

The best is Smooth-Sil 940 (or 950) because it is better able to take the heat- literally hundreds of casts and the mold may never wear out if cared for properly.

I used to prep my figures by embedding them halfway into clay- but many clays are problematic and can denature the RTV- or dont give a smooth transition line where the model meets the clay. Recently I switched to wax- carving and shaping a perfect mold line:
http://www.deviantart.com/deviation/49856263/?qo=6&q=by:stripwalker+in:scraps&qh=sort:time

I've also taking to doubling the size of my molds- so that the pour chamber is 5-8 times the volume of the bit I wanted cast- the increased weight on top increases the pressure within the cavity and I found I'm getting near 100% detail with the metal I use so that I have not pulled my spin caster off the shelf yet this year.

 

[kilted vampire]

What is mold max and smoothsil? Is it silicon based and where can you get it? Price? Have you ever tried Vulcamold? Do you use a wooden frame? I am very interested but would like to get better at casting first.

 

[Big Miller Bro]

The RTVs I use are from www.smooth-on.com (I use their liquid resins so that way I know what is compatible with each RTV and what isnt from their lines). Although post curing isnt needed I do it for my drop cast stuff to make the molds tougher.

http://www.smooth-on.com/liqrubr.htm

Smooth-On’s new Mold Max™ silicones are the choice of model makers because no release agent is required when casting urethane, polyester or epoxy resins, and castings are easily painted. Silicone rubber will also withstand the high temperatures of tin, pewter and other low-melt metal alloys.


Mold Max™ Series (Condensation Cure) - Smooth-On's new line of tin-cure silicones that feature low mixed viscosities with high tear strength and knotty tear propagation.

Smooth-Sil™ 930, 940 & 950 (Addition Cure) – No post curing required and cures with virtually no shrinkage. Ideal for reproducing exact detail of any model. Hardness: 30A,40A & 50A


I've never used vulcamold but know some folks use it. I used micromark stuff back in the 90s too.


The real trick is setting the mold up- embed the figure halway, I use candle wax rather than clay now.

http://www.deviantart.com/deviation/49856263/?qo=6&q=by:stripwalker+in:scraps&qh=sort:time

I put the embedded figure on a sheet of flat styrene then build a mold box out of Lego blocks (makes it really easy to get uniform molds of various sizes). Drip a couple blobs of wax onto the the base of the embedded figure to keep it from floating around when you pour the first half of the mold and set it in the lego mold box. I then seal the outside rim of the Lego mold box to the sheet of styrene with some clay (non sulfar clays only) so that the RTV wont bleed out the bottom. Calculate the volume then pour the RTV.

24 hours later peel the mold box off the sheet of styrene and flip it upside down. Gently pick/cut/melt the wax out leaving the figure now embedded halfway into the RTV instead of the wax. Trim any excess RTV and cut a 'mold key' if you didnt add a wax or glass bead one before pouring. You want to be sure that you have a nice half of a mold showing so keep your cuts small and clean and be sure not to wiggle any slack into the figure/RTV area. Then apply a release agent- they say not to use vaseline cause it will damage the RTV but I've had enough molds turn out to be giant cubes of rubber with an original sculpt trapped deep inside so I use dry skin lotion / hand cream and gently rub it all over the RTV but NOT over the figure itself since it will just fill detail. Build up the back half of the Lego Mold box and then pour the second half.

edit: some more tips and reference: http://groups.msn.com/SculptingMiniatures/makingadropcastmold.msnw

 

[kilted vampire]

This is most helpful. I am getting a much better picture of the process. Thanks Bro!

 

[Big Miller Bro]

well be sure to ask if you have questions