[Aluminum Birdcage]

Corvette Grand Sport #002

"The Birdcage" is the structural backbone of the otherwise-fiberglass Corvette body. It locates the relative positions of the front and rear clips, firewall and seats. It carries loads across the door openings and contains support and mountings for door hinges and latches.

A quick, economical and nearly undetectible "shortcut" in the construction of a duplicate body for the Corvette Grand Sport would have been the use of a production, steel birdcage from a mid-year Corvette.

That idea is quickly discarded, however, when you consider the essence of the original design of the Grand Sport: Light Weight! Unlike the production Stingray, the Grand Sport birdcage was originally fabricated of aluminum for a substantial weight reduction.

Since the owner is intending to participate in vintage racing, power-to-weight ratio is as important to this reconstruction as it was to Zora's engineers in 1963.

The fabrication presented many challenges, not the least of which was the use of authentic rivet and bonding techniques over more modern processes. The results justify the effort.

Some of the tooling built to fabricate the new aluminum birdcage "A" pillar main panel.

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New Aluminum "A" pillar main panels, right and left side.
New tooling to fabricate the "A" pillar top panel.

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New "A" pillar top panel after forming over tooling.
New "A" pillar assembly. This hinge area weighs less than 2 1/2 lbs. assembled.

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New "B" pillar panels, right and left side. Weight: 1 lb.
This is the new aluminum sub-assembly at the windshield base. The top and bottom panels of this sub-assembly were made from hammer-forming over a street-production steel birdcage structure. Very tough part to make out of 6061 aluminum...

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To make the panel at the top of the "A" pillar, a steel panel from a street-production birdcage was used to make a mold for the aluminum panel needed.
Devcon mold made of the steel panel.

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Top and bottom Devcon mold made to form the new aluminum "A" pillar top panel.
The finished 6061 aluminum "A" pillar top panels.

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Hammer form and clamps for production of panel located at "A" pillar and lower windshield inside corner.
New formed aluminum panel from above tooling, right and left sides.

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Newly fabricated "B" pillar top panels, for both sides, inside and outside locations.
Miscellaneous panels and brackets for front "A" pillars.

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New gell-coated plaster molds for driver's side sill panel, "A" pillar and "B" pillar. Ready to lay up new fiberglass parts.
These pictures show how critical all dimensions are for the aluminum birdcage and mating fiberglass parts.

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Here you can see how the "A" pillar aluminum structure fits inside of the fiberglass panel like a "hand in a glove".
New form block is fabricated out of wood, fiberglass filler and aluminum for the birdcage panel directly behind the seat area. The new panel will be formed out of 6061 T4 aluminum and is the main structural member for the new birdcage.

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This aluminum panel, despite its size, weighs only 3.5 pounds and is unique to the two Grand Sport roadsters.

The original coupe version of the rear bulkhead was much simpler in design but was replaced with this curved panel during the roadster "re-engineering" process by Arkus-Duntov.

The new aluminum panel assembly (as original) is bonded & riveted to the fiberglass floor pan, center tunnel, "B" pillars, sill panels & rear panel.

The new aluminum Grand Sport birdcage structure starting assembly. The steel cross-braced fixture was built on the original G.S. #002 body to assure that the new birdcage's critial points are identical. A large number of Cleco fasteners are used as the structure is fit together.

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The main sill panels are clamped to the surface plate and, using measurements from both the production Corvette birdcage and what is visible on the original Grand Sport birdcage, the structure is carefully fit together. Everything has to be correctly located prior to the riveting and epoxy bonding step.
View of windshield base and the top of the "A" pillar as it is being assembled with epoxy. Note the steel fixture used to locate critical edges. Clecos and C-clamps hold the parts until the epoxy sets up.

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Windshield area of the aluminum birdcage after assembly with epoxy and rivets. The steel fixture will be re-used when bonding the fiberglass to the birdcage in this area.
New, exact-reproduction, aluminum birdcage ready for installation of new fiberglass panels. Weight is only 21 lbs., less than a third of the (70-75lb) weight of a standard production structure.

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Louvered Hood
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