Rotocasting basics

[bridgeman]

I am trying to cast small parts - gaming dice - by rotocasting polyurethane (EasyFlo). At the moment I'm just doing 18mm cubes to get the hang of it. And I don't have a rotocasting machine so I am doing manually.

What I find is that the material seems to accumulate in the corners of the dice, and the faces are thin, and tend to bulge. I'm not sure if this is two separate issues - the unevennness and the bulging - or whether they reflect the same problem. It's fairly consistent - ALL the faces are thin and bulging.

As I say, I'm just doing it by hand and want to build a rotocasting machine and hope that this will help. Because the parts I'm casting are small I don't need powerful motors so I think I can have two separate battery-powered motors rather than trying to gear one motor. But before buying the motors I need to have an idea of the right revolution speed for what I'm doing. I'm assuming that slower is better, so that the material has time to settle on the faces rather being constantly sloshed into the corners, but am I right, and if so how slow is slow enough? And is there anything else I should be aware of, given the difficulties I've experienced with my initial experiments?

[bridgeman]

This is what it looks like from the inside:


i.e. almost all the material has ended up in the corners

[mangozac]

Hi Bridgeman, welcome to RA! Sorry for the late reply

I've not done any rotocasting before, but I suspect it could be an issue of your technique doing it by hand. How exactly do you rotate it?My understanding is that it's important to use the correct speed and motion to get rotocasting to work properly without thin areas as you're experiencing.

How soon until you can get a rotocasting machine?

[bridgeman]

I've made the machine - will maybe post a video of it when I get a moment. The two axes both rotate at about 8 rpm. I might be able to slow it down by reducing the voltage. I'm using a different resin - the Easyflo version specifically meant for rotocasting. The results are OK-ish but the material still has a tendency to accumulate in the corners. I'm thinking that this is a consequence of physics, the shape of the mould, and its small size, and that there probably isn't much I can do about it.

[mangozac]

You will always get accumulation in the corners - as you say, that's just the physics of it. With the right rotation speeds though you should be able to ensure that you end up with sufficient resin on the sides as well though