Jose Balderas

Part 3: Casting

Part 3: Casting

Now that the molds are made and materials selected, its time to cast. At first this can be a messy process, so make sure you have taken measure to control the mess. If you don't have the equipment I use here, you can still get by. Though optimal parts won’t be achieved. 


Coat and Clamp the Molds

Let's begin by closing up the mold we made. Before we do, it is important to spray the molds with a releasing agent. Otherwise, the cast could break as you try to remove it from the mold.

I like to first torque the bolts down by hand, then snug them with a wrench. Careful not to over tighten the bolts. You risk breaking the mold.

Mixing and Minimizing Bubbles

There isn't any leeway in this step of the process. Specific mixing instructions come with every compound and additive that's available. We just have to make sure the measurements are precise and mixed thoroughly. 

Once mixed, stick the mixture into a vacuum chamber to pull out the bubbles. Be wary of the pot life. The urethane can begin curing before you inject. 

Observe the bubbles rising from the mixture. At first, you'll see a bombardment of them. After a few minutes only a couple will be seen rising, thats when you pull out the mixture.

Injecting and Curing

When most of the bubbles have been removed, it's time to fill up the syringe and inject. Before injection, tilt up the syringe and smoothly push out any trapped air inside. Think of a nurse removing air out of a syringe before vaccinating. 

Bring the tip of the syringe to the inlet hole and inject steadily. Continue to push out material even after its filled. Bubbles that are trapped inside the mold begin to make their way out as the urethane flows.  

Now let is sit and cure. If you have a pressure chamber, now is the time to stick it in.

Opening and Reviewing Results

When the cure time of the urethane has passed, its time to crack the mold open and take a look. 

Observe where bubble might be. If they seem trapped due to circulation, add air vents. If they're randomly everywhere, they need to by vacuuming or pressure. 

A little flash is normal, you can see some as I rotate the washer. If you are getting way more than that, then you might be having sealing issues. Try tightening the mold a bit more.

Its common to go through a couple of iterations on a mold. Especially if the part you are creating is complex. 



Thank You,

For taking the time to go through all three parts. I hope this guide was clear and is helpful enough to get you started on designing your own. If you have any questions or need help on making some cool stuff, please reach out.