Design: John Simpson Architects International, London, UK
Technical Drawing: Stantec Architecture, Chicago, USA
EAST ENTRANCE ACROTERIA
Matthew and Joyce Walsh Family Hall of Architecture
University of Notre Dame, South Bend, IN, USA
I had never heard of an acroterion when I started work on the Notre Dame School of Architecture’s new building.
Acroterion is the Greek architectural term for a pineapple-looking thing that is perched in a prominent position on the rooftop of a Classical or Neoclassical building.
A herd of acroterions is called an acroteria.
An acroteria is challenging to manufacture.
All 3D CAD modelling, CAM machining, graphics and text: Cam Frith
unless otherwise noted
Design: John Simpson Architects International, London, UK
Technical Drawing: Stantec Architecture, Chicago, USA
Design: John Simpson Architects International, London, UK
Technical Drawing: Stantec Architecture, Chicago, USA
Once the CAD modeling was completed in Rhino, we determined how best to approach the manufacture of cast stone parts.
Due to the desired level of detail and finish in the final parts, we elected to machine positive masters, to be cast in rubber, to create negatives into which stone would be poured.
The most obvious obstacle in machining masters is the geometry itself:
There are no planar surfaces to secure to the machining table.
A second challenge in machining the master for the central acroterion involves the angle at which it perches on the rooftop.
The angle of the V-notch at the base of the acroterion is not 90° to the face of the piece, making it considerably more problematic to mill on a simple 3-axis mill, which does not have the ability to tilt the tool in relation to the table.
The solution involves machining the master from a two part blank:
MDF on the face (brown), where a high level of detail is required, and
EPS foam on the back (white), which is faster to machine and allows the blank to be wirecut to a different angle partway through the milling process.
The two sections are permanently glued together with a two-part epoxy and placed in a vacuum press to ensure maximum adhesion.
The machining process for the center acroterian is as follows:
STEP 1:
The blank is secured to the table with the angled EPS face down.
The V-notch is cut into the blank at the appropriate angle, due to the angular shape of the blank.
STEP 2:
The blank is placed MDF side down on the CNC hotwire cutter.
The angled EPS foam portion of the blank is trimmed parallel to the MDF face.
STEP 3:
The blank is secured to the mill with the MDF face up.
STEP 4:
The front face of the acroterion is milled into the blank, to a depth just below the MDF layer.
STEP 5:
A jig is designed and milled to securely hold the blank.
STEP 6:
The milled blank is secured into the jig, with the newly-milled front face down.
STEP 7:
The back of the acroterion is milled to shape, completing the process.
