After finishing my "Rotocast machine" I need to make rotocast forms for this machine.
I need forms that can be pressed in to the machine without deforming.
The first test is to make a casting form of the gate house.
The process of making a rotocast form starts with the so called “master” object.
In this first test I replace the master for a foam form that has exactly the same form and size as the master.
For this first step I need the master form, river clay, wooden sticks an a round piece of wood, thin metal plates, some adhesive tape and Talcum.
The first step is to wrap the gatehouse form in to a layer of clay. The clay is rolled flat between 2 wooden sticks of approximately 5 to 7 mm thick,
forming a thin and equal flat pieces. For this I use a thick round piece of wood that I roll over the clay.
The talcum prevents the clay to stick on to the round piece of wood.
Clay pieces are pressed on to the object forming a mantle of clay over the entire surface.
Joints are being filled using water to butter the clay up.
Once the whole object is covered with clay thin metal plates are pressed in to the clay on either side and on top.
The object is now divided in to two pieces (a front and a back piece if you like).
I fix the plates with lumps of clay on the bottom side and use adhesive tape to connect the top metal plate to the left and right plates on the sides.
The first stage is done. Next step is to build up the so called fiber mantle of the casting form.
For this step I use Vaseline, Epoxamite, Fiberglass, two brushes, and Aerosil.
First of all I use the Vaseline on the metal strips.
This will help me in splitting up the form later on. Next I use Epoxamite. Epoxamite is a mean material so ventilate well and use gloves.
I use the plastic gloves you get for free at the gassstation. You need a fresh pair for every run you do using Epoxamite.
I make a batch of epoxamite and grease the whole form with the stuff. Straight after that I start adding strips of fiberglass on to the wet surface.
(best is to have strips of fiberglass ready so cut of enough before starting the work with Epoxamite).
After the first fiberglass layer is done I grease a second layer of Epoxamite on to the surface. In this run I add Aerosil.
Aerosil is a very mean material. This stuff is lighter then air and is so fine that you inhale this stuff easily.
That you do not want so use a mask! Take the right precautions and all is well.
You do not need to work with Aerosil but it does give your Aerosil more volume so the layer you grease on is thicker.
Add a second layer fiberglass and you get quite a solid mantle. The whole process goes reasonably fast but you might want to do this in two batches.
If so, the You need two brushes. Once the Epoxamite start its chemical reaction it gets hard quickly and you can throw away your brush.
Now the epoxamite is hard you can cut, drill, saw and sand it.
Beware that fiberglass threads that where flexible during the greasing process are now hard and when they stick out, sharp!
You do not want to have fiberglass splinters so wear gloves at the start of this stage.
You can scan the surface for sharp bits and pieces cutting and sanding them away.
Next you can use a sharp knife or screwdriver to get in between the metal plate and the hardened Epoxamite.
I use a kind of pliers to draw the plates out.
Before trying to split the mantle open I use a saw to cut the three sides and sand them.
After that I drill holes through the edges so I can fix this form later on in the actual casting process.
I split the mantle open using a screwdriver trying to open the form slowly and steadily bit by bit from side to side to prevent damage to the mantle.
Once its open You will see that the clay sticks to the mantle. So now you need to scrape that out.
The clay itself is still good enough for a possible next form. Store it away in a plastic bag with a few drops of water for later use.
The mantle is quite sturdy so after a thorough scrub I also use warm water and an old toothbrush to get the tiny left over clay bits out.
If I put the mantle over the form You will notice that there is a space between both that equals the thickness of the clay layer.
This is exactly what we want because now we can cast the actual silicone form.
For this step I use a piece of wood, a drill, some screws, clay, universal mold release, silicone and a funnel.
To cast the form I start with fixing the master on to a piece of wood with some crews.
I use Universal mold release on the surface of the gatehouse so the silicone will get off more easily once it is dry an I add a lot of
Vaseline to the inside of the mantle for the same reason. In the wooden base are a few tiny holes for letting the air out and a larger hole that I can
use to poor the silicone in. Once the master is fixed I fix the mantle that goes over the master.
I seal the edges of the master off with clay and hang the whole shebang upside down in a bucket.
I start mixing the silicone and place a funnel in the big hole. Now the casting starts, small batches at a time.
Once silicone is oozing out of the little holes the form is full.
Once the silicone is dry the mantle can be opened and the silicone form should easily come loose from the mantle.
The master can also be removed from the form leaving a big hollow silicone form.
With the silicone form and the mantle to give the form support during the rotocast process I now can start casting.
As you know by now, using rotocast forms is quite an undertaking. It is a lot of fun to sort it all out and making the forms.
For me this is as much part of the hobby as the sculpting or painting is.
I still need to do a lot of testing especially when it comes to making these forms and the materials used.
I will try to update the article if I made any kind of progress in the process.
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