Tips & Tricks Rotocast

Rotocasting machine

Introduction:

Imagine you're able to cast a 3D object in only one cast (a house for example). No assembling needed and you even save on materials. Now that would be a great time and money saver.
Nothing wrong with designing a house and casting the 4 sides a part. The results look great so that’s fine. But it takes a long time to cast all the parts (6 casting runs for a house like the ship themed ones) and there is quite some assembling involved as well.

Building the machine:

I designed a simple rotating casting machine that is operated by hand. For this I bought some MDF a round stick of redwood, wire-rods, nuts and wing nuts, rings and a paint roller.
After drawing he design I was able to make the machine in a single afternoon cutting the wooden pieces and gluing it all together. I designed quite a heavy foot in which the arms that lift the rotating part rest.

The rotating part is made out of 2 wooden disks with a diameter of 30 centimeter and 3 round redwood sticks of approximately 60 centimeters long. Alongside the three redwood sticks I placed three wire-rods. The outside disks and redwood sticks are fixed with Wood glue and screws. The wire rods are fixed with rings and bolts. At first I added a single round disk in the rotating section that is used to fix a form in its position. To get this to work I use wing nuts. I added another round disk later on so I am able to do two rotation casts in one session.

To get the machine operating I added a handle made out of a paint roller. Since the rotating part moves quite smoothly it isn’t essential to have a handle but while casting it is nice to use the handle as an alternation. To fix the handle firmly on to the machine I made a resin connection as shown in the pictures below. I fixed the roller in a two cast session. First I cast the roller in a disk and put the top of a plastic bottle over it while the resin was still wet. The second run I filled the plastic part. Although it is not an essential part it was fun making it and since it works I want to share this experience as well.

Operating the machine:

The machine only operates when using special rotating moulds. Making these molds is explained in the Tips & Tricks topic “Rotating molds” so I only focus on how to put the mold in the machine.
A rotating mold is open on one side that has to be closed while in use. To get it closed I use a silicone sheet of a couple of millimeters thick. This it laid over the opening. The round disk is being pressed against it and fixed using the wing nuts on the wire rods. The form is now closed and ready to be used

Since resin is as thin as water you might get leaks. Nothing to worry about as long as the resin doesn’t poor out. You only halve a twist on one or more wing nuts a bit that might do the trick. Just in case I lay an old piece of cloth underneath the rotating part to prevent the resin drips falling on to the foot of the machine or table.

Operating the machine means you have to rotate the cylinder for some time. Depending what type of resin you use you need to operate the machine for 10 to 20 minutes. The rotation speed is quite slow and just to be sure to get the resin in all the right places I turn over the machine a few times to the left and the right.

To get an indication of the chemical process I keep a few drops of resin near the machine so I can see when the chemical reaction is done. I set the mold aside so the resin can harden a bit more. After about an hour I can open the mold and get the cast out.

On to the Rotocast form

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