About Me

My photo
I make toys for kids who don't want to grow up. I'm on the lookout for new projects. If you're interested in commissioning me to build something ridiculous, shoot me an email.

Saturday, March 15, 2025

Genestealer Update 23: Molding and Casting the Knees and Elbows

 When we last updated this project, we had finished texturing the sculptures for the knees, elbow, and tail:Genestealer sculpts

Since then, we made molds for all of them and started casting rubber parts:
Happy with the Fit

To see how it was done, read on

With the clay sculpts done, the next step was to make molds.  Since we'd be making rubber parts, we'd need rigid molds.  In this case, we're making hollow silicone castings, so we'd need two-part outer molds with a core inside to define the inside shape of the cast parts.

The core would be the 3D printed piece that we used as a sculpting armature.  To make the two-part outer mold, we'd start by building a parting wall using WED clay:
Building Parting Walls

We used WED clay because it's water based and would be easy to clean off of the oil-based clay sculpture.  Here's Jeff helping me set those up:
Building parting Walls

This is a dimly-lit pic of the tail with the parting wall started:
Parting Line Set Up on Tail

Because I'm a terrible photographer, it fails to illustrate the registration dimples I pushed into the surface or the watertight edges along the surface of the sculpt.  Really I should've taken the photo when the wall was all polished and smooth, not when it was half done like that.  I don't know what I was thinking.  I apologize for this shortcoming.

You can almost make it all out in this pic where I'm starting to apply an epoxy-based gelcoat to the surface:
Gelcoating Tail Mold

The gelcoat captures all of the fine details on the surface:
Applying Gelcoat to Tail Mold

Gorgeous:
Gelcoat on Tail Mold Side One

Here's all four molds with the gelcoat applied being set aside to cure overnight before reinforcement:
Gelcoat on Knees, Elbow, and Tail

Once the gelcoat had set up, I used some Plasti-Paste Epoxy (a trowelable plastic compound) to fillet the hard corners and smooth over the peaks and valleys of the gelcoat.  Then I laid up a healthy thickness of fiberglass:
Knee Mold First Half

Here's side one of all four molds laid up:
First Side of Knees, Elbows, and Tail

The next day I removed the WED clay parting walls, washed off the residue they left behind, then sprayed a thick coat of release agent onto the first half of the molds and the clay sculpt before gelcoating and fiberglassing the second half.  Then they set overnight to cure again.

The next next day the molds looked like so:
Elbow Mold Ready to Split

All I needed to do was to pry the two halves apart with a pair of flat head screwdrivers:
Elbow Mold Separated

To make it a little easier, the clay inside was softened by placing the molds in front of a heater in the shop.  Even so, it took some doing to get the molds open.  Here I am forcing the tail mold apart:
Pulling Tail Mold Open

Ta-da:
Tail Mold Separated

The original 3D printed sculpting armature inside was pretty smooth and the sculpted texture inside of the outer mold was pretty rough, so the clay mostly slipped right off of the armature and stuck to the inside of the molds:
Tail Mold Opening

So this here is the tail core all nice and clean after a quick wipe down with a rag:
LOOK AT MY SEXXY TAIL!

After cleaning up the edges of the fiberglass molds, the clay that was stuck to the inside of the fiberglass parts needed to be peeled and picked and scrubbed out.  This particularly tedious pain-in-the-butt chore was perfect for Jeff:
Jeff Scrubing Molds

Jeff loves this sort of thing:
Creepy Jeff Scrubbing Genestealer Molds

While Jeff was going through the tedium of scrubbing the oil-based clay out of the molds, Rachel sewed up a set of plurple powermesh fabric sleeves to fit over each of the mold cores:
Powermesh Reinforcements Sewn

Meanwhile, I drilled a series of holes around the base of the armature (which would now become the core of the mold) to allow rubber into the space between the outer mold and the inner core.  Then I bolted the whole thing back together and it was ready to pour:
Elbow Mold Ready to Pour

Just like the flat fleshy parts we made before in update 20, these fleshy parts will be cast in Dragon Skin silicone with a mix of red, blue, and a teensy bit of white pigment from Smooth-On's Silc Pig lineup.  Then it all gets mixed together before vacuum degassing.  The degassing chamber is always fun to watch:
Degassing Plurple Tinted Dragon 
                                                                                                            Skin Silicone

Once all of the bubbles had been evacuated from the liquid rubber, I pour it into the mold:
Pouring Silicone into Elbow Mold

But it turns out to be way too viscous to easily drool its way into the holes I drilled, so I ended up having to use a syringe to force it into the mold:
Injecting Silicone into Elbow Mold

The whole hole was filled to overflowing so there would be excess silicone to flow into the mold if a stray bubble worked its way out:
Elbow Casting Overflow

The next morning, it was time to open up the mold:
Demolding the First Elbow

And then peel the cast silicone sleeve off of the inner core of the mold:
Sleeve Demolded

The resulting sleeve was not too shabby:
First Sleeve Cast and Demolded

It was, however, a little loose on Rachel:
Rachel Tries Genestealer Elbow

It did fit me pretty well:
Slipping into the First Elbow Sleeve

It'll be even better once I trim off the excess powermesh fabric from the ends:
First Elbow Sleeved

But this?  This will work:
Genestealer Gun Show

Since I was excited, I couldn't resist the temptation to slip on the arm exoskeleton shells and check the fit in the dirty shop mirror:
Dirty Mirror Test Fitting

Turns out I forgot to tuck in the little flat bits in the holes in the sides of the arm:
Tucking in the Arm Meat

Still, it looked pretty good:
Elbow Meat with Exoskeleton Arm Shells

Right Arm with Meat Installed

So that's a thing!

As I write this, the second elbow is curing in the mold.  The tail and knee molds need a bit more cleaning before they're ready to pour.

Next on my way up the ladder of increasingly complicated shapes to mold and cast in silicone will be the shoulders.  Then the feet, the hands, and the waist/hip section.  Then finally the head.

Stay tuned!



No comments:

Post a Comment