2.3_semacode door knob [casting process]


Once the molds are ready, it’s time to do the casting. The logic is that with flexible mold, you want to cast a hard material into it and vice versa, i.e. (hard) foam positive – (flexible) rubber negative – (hard) plastic cast or (hard) wax negative – (flexible) rubber cast.

Ventilation and pouring holes were added manually at this stage.

The molds were clamped with just enough force to keep them together whilst maintaining the shape of the doorknob.

Smooth Cast 300 Liquid Plastic (Polyurethane Elastomer) consists of two parts (A & B) which when mixed up together (1:1 ration) became reactive. It has a pot time of 3 minutes and 10 minutes cure time. Really useful for casting multiple times quickly.

HMIS (Hazardous Material Identification System):
Health = 2 (harmful by inhalation, irritation on skin)
Fire = 1
Reactivity = 1

Gloves and safety glasses must be worn when working with this material in a ventilated area.

The poured Smooth-Cast started to dry up after 3 minutes.

Each knob was cast using 5 oz of the liquid plastic. It was enough to allow the substance flowing out and around the edge of the rubber molds.


We experimented with the primary colours including the red pictured below. It’s found that 10 drops into the Part B this would give vivid colour to the cast. 2-5 drops were not sufficient and left the objects pale-coloured.

White Knob (no colouring).

Cheese Yellow Knob (2 drops of red and yellow).

Blue Knob (5 drops).

Red Knob (10 drops).

The American Knobs.

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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