Rotocasting- random or orderly motion?

[helix_3]

I'm considering building my own hand-operated rotocasting machine, but I'm hearing conflicting perspectives.

On one hand, Robert Tolone is a very talented mold maker/ resin caster and advocates for random, continuous motion. His videos show this technique working for small and large-scale castings. On the other hand, literally every other rotocasting machine design I can find online uses a mechanical linkage to get ordered, regular motion.

Which design should I choose? I'd personally prefer to skip the gears and belts, but I also want to make sure I'm making the right design choices before preceding.

 

[joberg]

Depends on what kind of resin/medium you'll pour into your mold. Doing what Robert does works if your medium doesn't look like water (you could be turning that mold like a mad Dervish for hours) Since you don't want to build a rotocasting machine you'll have to experiment what works for you. I use the random with simple pieces (not too many ''nooks and cranny'' details. I use the orderly motion with a complicated, detailed piece and a more liquidy medium.

 

[JPH]

Have you ever rotocast before?

It depends on the mold. Some molds I can just do my usual roto-dance, and some require you to address specific areas repeatedly or they come out thin.

Any spikes will require extra love, because if they clump off at the base, then resin wont go to the tip.

Are we talking a fast-sett8ng resin, or one that takes hours to cure?

Are we talking shallow detailed, round cast or assymetric, spiky cast?

 

[helix_3]

I use the random with simple pieces (not too many ''nooks and cranny'' details. I use the orderly motion with a complicated, detailed piece and a more liquidy medium.

That's interesting- I will start simple but may want to go more complex in the future. Does ordered motion still work fine for simple pieces? If so, I should probably just commit to making a higher-end version from the start

Are we talking a fast-sett8ng resin, or one that takes hours to cure?

Are we talking shallow detailed, round cast or assymetric, spiky cast?

I haven't actually gotten into researching the resin, but I assume I'd want a fast-curing resin so I'm not standing there all day. Is there any downside to that kind of resin?

Also when you say spiky, is it specifically long, thin "spikes" that cause problems, or just fine detail in general?

 

[lmgill]

I'm not sure how you would build a random motion rotocaster machine. Unless the mechanics were very poor.
Consistency and versatility is what you want.
Constant, from the standpoint that when you find a speed and direction that works for the material and the mold, you can repeat the successful movement and speed accurately.
Versatile, in you will want to have the ability to change the speed of the axis of rotation independently from on another.
Example, a long cylindrical mold will want a faster rotation around the diameter of the cylinder, while a slower rotation along its length.
Most professionally built rotocaster have 2 independent motors, so x and y rotations can be controlled independently. It is also important to be able to position your mold in the center of these two rotations. (A mistake a college of mine made many years ago, by building a rotational caster with a car differential)

Cure time is not so much about fast and slow, as it is the cure curve. Is the resin "liquid, liquid, liquid, Boom - solid", or does it gradually get thicker.
Whenever I hand rotate a mold, I leave a small amount of resin in the mixing cup, so I can periodically pick the cup and turn it to see the viscosity of the resin as it cures. This helps me visualize what the resin is doing inside the mold and adjust my rotation speed accordingly.
I have seen people consistently rotating a mold to quickly, and as a result, the resin isn't given enough time to spread out. With most resins, the more mass the quicker it will set up, (Exponentially so) a big lump liquid will cure much faster, than the thin coated surface, so rotating the mold in a way that reduces this mass of material in one spot, is key.

 

[JPH]

So, I am a big fan of smooth cast 325. Starts clear, you mix it and actually feel it *Pop* (start to heat up) that is when it is ready. Dont mix too aggressively or it gets alot of bubbles.

You pour it in your mold and do your rotodance. You maneuver the pool of resin (the smoothcast) trying to spread it evenly throughout the mold. While it is most liquidy, aim for fine details and projections off the main mold body.

So, if molding a helmet with spikes or a mohawk, get the resin in the mohawk or spikes early. When the resin starts to thicken, you will see it slow down...but it will still keep moving for a while. Try to find a place to land the clump, a spot where the resin can settle. If you try and move the slowing clump over a protrusion off the main mold, the slowing resin could block the entrance to the protrusion, or get stuck in it with an air pocket.

Either way, "random" is bad here.

I'd use a random machine for a slow curing resin on something that just needs one big pour, without too many protrusions.

 

[joberg]

As you can see, lots of great advices here : JPH, Imgill and lots of possibilities and variations
Medium (type of resin or other)
Mold
Rotocasting machine
Details of the piece being rotocasted