02. Mold and Cast: family turtle

Edrie Ortega []


This design focused on making an object that could be casted for each of my family members. The turtle with the “O” represented my favorite animal with my family name. Initially, the turtles were suppose to be able to stack on top of each other. However, complications within the process made this aspect unsuccessful. The overall project was fun.

There are 3 parts in completing the mold and cast. 1. Mill the positive 2. Cast the negative mold, 3. Cast the final  positive mold.

Mold 1: 6″ x 3.5 ” x 1″ Wax block

Machine: Shopbot

Rough =10 min.

1/4″ ball nose

Spindle Speed= 9000


Pass Depth= .25

Flakes are a great sign of appropriate speed for milling wax. If too fast, the heat of the bit will melt it.

After a few rough cuts comes the finish cut.

Machine: Shopbot

Finish = 40 min.

1/32″ ball nose

Spindle Speed =9000

Stepover = 15%

Pass Depth= .125

Feed Rate =4

Plunge Rate= 4

The design on the shell didn’t come out correctly. It most likely was how I designed the depth of the letter. It also showed a bit of melting.

So I gave it a face lift. To fill the holes on the shell, I used hot glue. Now time to cast the mold!

Mold 1: Mold Star 15

Pot time -50min.

Cure Time- 4 hrs.

So many choices…

Mixing the solutions together was very simple.  Its a 1:1 ration of each chemical substance.

After applying a release agent, hand soap, the Moldstar 15 was poured to the top. After  waiting and waiting and decided to wait overnight, it was ready.

You can see the excess amount of pink hand soap used when peeled from the wax. The amount of soap caused a ton of tiny air bubbles in the mold.

The first mold also did not go into all of the crevasses. This will not be able hold the solution for the next step. Time to REMOLD!

The second attempt was again left overnight. Less amount of release agent was used and therefore little amount of air bubbles. SUCCESS!

Cast 1: Smooth-cast 300

Pot Time= 3min.

Cure Time = 10min.

The far right cast cured before the mold was full. By the 3rd attempt, the casted mold showed great progress but there were still problems with air bubbles. So I decided to experiment on a stiffer rubber.

Mold 2: PMC 121/30

Pot Time =30mins

Cure Time= overnight/16hrs.

The mold is beautiful.

This time, I clamped the mold together with rubber bands and plugged the original pour and ventilation hole with one of casted turtles.

The new pour hole will be located at the head of the turtle.


4.196 Special Problems in Architectural Design Complete Fabrications Nick Gelpi Mon-Fri, Jan 5-7, 10-11, 13-14, 18, 20-21, 24-25, 27-28, 01-04:00pm, 3-402/7-432studio, 1st mtg Wed 1/5 Pre-register on WebSIS and attend first class. No listeners Prereq: Permission of instructor ; Yr-1 MArch students who have completed 4.123 only Level: H 9 units Standard A - F Grading Can be repeated for credit Lab Fee: 150 A comprehensive introduction to methods of “making” explored through a wide range of brief but focused exercises. Skills = developing complex geometries from flat components; fine-tuning press fit construction, molding and casting, and making repeatable molds for customization. A two-part workshop, the first half will contextualize contemporary tools and techniques within the trajectories of historical case studies of building, combined with hands on familiarization of tools. The second half will implement the tools of our workshop in the context of Design. Working on group design build process for three MIT 150 FAST installations, students will test and influencing designs through the instrumentality of production. These hands-on design build projects are intended to produce reciprocity between skills and design, making more complete the problems of fabrication. Subject limited to year-one MArch students who have completed core-1 studio. Contact: Nick Gelpi, 9-224, 253-9415, -


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