Week 8: Molding and Casting

Introduction

This week, I molded and casted the letters ‘ClassRate’ for my final project

Design of the logo

I used TinkerCAD to make the logo because TinkerCAD comes set up with letter shapes. I measured the width of the box that I was putting the logo on, and then adjusted the size of the letters accordingly. Each letter was 8mm wide, 15mm tall and 2mm thick.

The design

Machining the wax

Then I used the ShopBot to cut out the logo. Molding and Casting requires some thinking on the positives and negatives of the mold! Since I wanted the individual letters, my oomoo should have a block with the indentation of the letters. In order to create an indentation of the letters in the oommo, I would need to pour the oomoo in a box with the letters sticking out. So that it what I did! I added a box to the design in TinkerCAD and had the letters sticking up from the box. I was using the 1/16 bit, but then the fine details of the letters didn’t come out (for example, the hole in the A), so instead I used the 1/16 bit for the roughing toolpath and then changed the bit to a 1/32 for the finishing toolpath. The toolpaths looked great, and then I machined the max.

Machining the wax
Wax with the letters protruding

Messy Oomoo

Now that I had the wax mold, I would need to pour the oommo. So I followed the instructions and measures equal parts of part A and part B of the oommoo mixture. I added about 100g of each. I mixed them well together in a beaker. Then, I placed the beaker in a vacuum and sucked out the air.

Mixing these two equal parts
Putting cup in vacuum

EXPLOOMOOSION! The oomoo exploded all over the chamber of the vacuum and made a huge mess. It blocked the valve for the vacuum and there was blue stuff everywhere. I cleaned everything up, and then tried again.

Exploomoosion

This time, I put the mixture in a larger cup so that it wouldn’t overflow as quickly. I put the vacuum on and stopped when the oomoo reached the top. The vacuum is used to remove bubbles. Once I had that, I needed to pour the oommo into the wax mold. Since my letters are very thin (2 mm thick), I needed to add a wall for the wax mold structure so that there the oomoo could be poured into it. So I added a wall around the letters. Then I poured the oomoo. I found out later that I was supposed to let the oomoo flow, but I didn’t know that, so when I poured it, I just poured it all over – this led to some small bubbles. Now, I waited for the the oomoo to dry. The box said it would take only 75 minutes, but I ended up waiting 5 hours before it was good enough to take out

Oomoo mixed and with bubbles removed
Wax with wall
Filled wax with oomoo

Hydrostone

Hydrostone container

The oomoo turned out well, despite a few small bubbles.

Now, I mixed the hydro-stone. I used about 50g of the hydro-stone powder and 16g of water. I then started pouring the hydro-stone mixture into the individual letters, but that was taking long and the hydro-stone was drying out, so instead I poured the hydro-stone onto the whole thing, and then smoothed it out with a wooden spatula. This was MUCH quicker. Now, I waited for this to dry. This didn’t take too long to dry – about a couple of hours. I have my molded and casted logo!

hydrostone mixture
Individually pouring hydrostone mixture
Faster method with a wooden spatula
Oomoo with hydrostone mixture
Result

SprayPaint

I spray-painted the hydro-stone logo.

Hydrostone spray painted