One of the biggest problems with building your own DIY equipment is the space that it takes up. If you happen to live in a small space and don't have a workshop to keep your kit in, it can very quickly become overwhelming.
A descent roto-moulding (or roto-casting depending on your terminology) machine is quite a bulky thing. Add to that the limited space that you have as a student (or freelance product designer) and you have a dilemma - you would like the equipment, but need it to be stored in as small a space as possible.

The solution to all of these problems comes with K'NEX. This child's construction toy is lightweight, strong, reasonably cheap and best of all completely adaptable for different purposes. These instructions will show you how to build a fully functional machine with a big enough space for descent models and projects.
This is prefect for small plastic casting, but also for more 'family friendly' projects such as Easter egg making (more on that later)...

Enjoy!

Step 1: Counter-balance (x1)

To begin with you need to construct the inside frame for the roto-moulder.
This can be done using normal purple connectors and white sticks. You also need to add some wheels to this part to add ballast.

Step 2: Motor (x1)

For the opposite side of the inside frame, you need to insert a motor (to do the first set of rotation). This is why you needed the wheels as counter ballast in step 1.

Step 3: Rigging (x2)

You need to build two of these parts. These connect the motor part and the counter balance part together together to complete the inside frame. These parts can be joined using the numbers indicated.

Step 4: Pivot & Motor (x2)

The next stage is to build the support structure for the inside frame. This allows the inside frame to rotate (thus spinning the material you are moulding around inside the mould).

Step 5: Main Body One (x2)

These pieces make the main bulk of the support, raising the inside frame off the ground enough for it to rotate.

Step 6: Joining Sections (multiple)

These parts connect the two main frames together, merely to give structural stability. Otherwise, when the motors are running, the machine becomes unstable.

Step 7: Rotating Section (x1)

The final part of the rotomoulder, this sits inside of the inside frame. This itself rotates, allowing for 3 dimensions of spin.
When you come to moulding, you attach your plastic mould to this part (I found elastic bands best).

Step 8: Testing

Once assembled, all you need to do is click the motors on and watch it spin!
The best technique is to start the inside frame one first, then the main support one.

You can then begin moulding!

Step 9: Moulding

Attach the mould you wish to use to the rotating piece using elastic bands. You can then start the machine rotating. Here, it may require a bit of a push to get going. Leave it for about half an hour or longer to let the material set properly.