2.2 – Mold Making: Process

Milled Mold

Material – 1.5″ foam

CNC – Shopbot

Roughing Pass: NA

Finishing Pass:

Endmill – 0.25″ Ballnose

Spindle RPM – 9000

Pass Speed – 10 inches/sec

Plunge Speed – 6 inches/sec

Step Over – 25%

Traverse: Along Y

Flexible Mold

Material – Smooth On: Mold Star 15

Mix Ratio – 1:1

Pot Life – 50 mins

Cure Time – 4 hrs


It was necessary to cut a much large sprue because of the material’s viscosity.  Original sprue diameter was 0.25″, however, a sprue roughly the size of a square inch was more appropriate.  The amount of material necessary was not taken into account when initially designing the mold.  As a result much more Mold Star 15 was required to fill the molds.  Approximately 56 fl oz was used.  Caution when mixing large volumes of the product because the bottom portion has a tendency to require extra mixing despite what appears to be an even mixture throughout the material.


Material – Smooth On:

Mix Ratio – 1:1

Pot Life – 7 mins

Cure Time – 15mins


Although the product’s information sheet states that the cure time was 15 mins it required at least 30 mins before it could be removed from the mold without altering the product’s shape.  Possible reasons: cooler room temperature, improper mixing of materials.

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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