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Acrylic Base with Wedge Supports

Context

The design started as a way to make an inexpensive, modular mould base for a roughly 70 × 70 cm monofin, while retaining the ability to reconfigure the same materials for bifins and other laminating work.

The A3-sheet idea moved beyond the initial experiment and became the base used for all laminating work.

Adopted design

  • Use six A3 sheets of 2 mm acrylic, bought as a pack for about £15 at the time.
  • Arrange four sheets in a 2 × 2 grid for the flat section, giving an area of approximately 84 × 59.4 cm.
  • Arrange two sheets side by side for the angled foot-pocket section, giving an area of approximately 84 × 29.7 cm.
  • Together, the sections occupy approximately 84 × 89 cm and can be supported on a standard 90 × 90 cm table.
  • Cover the table with a protective plastic sheet before assembling the acrylic.
  • Bridge the joints between the acrylic sheets with electrical tape. Its flexibility was preferred to the greater stiffness of packing tape when the assembly is pulled under vacuum.
  • Raise the foot-pocket section with plastic stackable wedges. No wooden backing or permanent support structure is part of the base.
  • Cut open the vacuum-bag film and seal it around the perimeter of the acrylic with butyl sealant instead of enclosing the complete assembly in a bag.
  • Form generous curved loops in the butyl at 90-degree corners. The blade does not occupy the corners, so the loops can use a large radius rather than forcing a tight turn.
  • Recover the acrylic sheets after curing so the base remains modular, reusable and compact to store.

The monofin layout supplied the original dimensions, but the construction method is also used for bifin and general laminating work.

Rationale

The tiled A3 sheets make a useful laminating surface without buying or storing a single large acrylic sheet. The separate flat and angled sections allow the foot-pocket transition to be shaped with reusable wedges. Electrical tape accommodates small movements between the sheets, while the cut-open vacuum film permits an edge seal around a base that is wider than the original 76 cm vacuum bag.

Later process change

The original discussion assumed PVA release solution over the acrylic and taped joints. The release process subsequently changed from PVA to wax, so the PVA-specific advice is historical rather than part of the current laminating process.

Qualifications and unresolved details

  • Dimensions inferred in the conversation from a CETMA monofin image were assistant-generated estimates, not verified measurements.
  • No final wedge angle or exact wedge arrangement was recorded.
  • The electrical-tape joints, butyl perimeter and support beneath the angled acrylic should be judged from their behaviour under vacuum; the conversation did not record formal leak, flatness or deflection measurements.
  • The suggested assembly times were estimates rather than observed timings.
  • Solvent-cleaning suggestions from the conversation are not retained as part of the adopted process because some solvents can contribute to crazing in stressed acrylic.