Rotational Molding Tips And Tricks

You can use molds designed for casting solid resin parts to rotocast hollow parts.


Such molds are usually heavier than the blanket and mother molds used for rotation casting. So the trick is to make a cradle that mounts them on a rotational casting machine so that they are carefully balanced. You also need a quick way to close the pour spout and lock the mold into place for rotation. In this video I build a cradle and demonstrate its use.

Once the mold is secure on the machine you must cast the resin into the mold using just enough resin to coat the surface of the mold. I usually use 3 small shots of resin to cast the part. If you try to cast the part in one heavy shot the resin will pool inside the mold and cure in a big lump resulting in a failed casting.

I put one shot of resin in the mold and cut open the resulting casting to show the evenly coated walls. I also show how the resin flows away from the high spots inside the mold. This creates weak spots in the mold and is also why you need multiple layers of resin to complete the casting.

In making hollow castings it is frequently necessary to pre-paint the mold to make sure that you don't catch bubbles in the finer details of the mold. That is because the rotation forces are not strong enough to push resin into those areas.


Here is a list of suppliers for the rubber, resins and waxes I use in my videos:
https://www.dropbox.com/s/kz6mhmf7v5v...

Do you have a project to suggest for the channel?
Here’s a .pdf with everything you need to know:
https://www.dropbox.com/s/pjb0l6fr7zj...

TIME STAMPS
00:00 Using a mold made for solid casting to hollow cast parts
00:25 Balancing the mold in a cradle designed to hold it on the machine.
03:54 Mixing the resin and adding pigment to color it.
04:44 Pouring the first shot into the mold and rotating it.
06:17 Opening the mold to evaluate the “clean-out” casting.
07:41 Cutting the casting open allows you to see if the shot volume was correct.
08:32 Using a light lets you set the thin spots in the mold.
11:05 Pre-painting the mold to eliminate bubbles.
12:50 Pouring the first of three shots into the mold.
15:12 Removing the mold from the machine and checking out the casting!
16:52 Close up inspection of the parting lines and flaws in the casting.
19:10 Thanks for watching!