WoodSkills Issue 02 - Page 68

68

Laminating curved sections using the vacuum press

The Process

Designing the laminated section

When designing the piece to be laminated, there are several factors which should be taken into account.

1. Curve direction and material : Most veneers prefer to bend in one direction only at any given point and the same applies to thin (1.5mm) birch plywood/ aeroply and thin layers of solid wood. That’s not to say that a compound curved surface is not possible with this method, but it is very much a matter of careful design and probably a few trials – caveat maker! For most projects, and for the purpose of this article, it is more useful to consider a one directional curve, several of which can be joined together at another point to create a surface with a compound curve.

2. Under-hangs: Areas which curve under the former, should also be avoided as these are points where pockets of air can get trapped in the bag and so pressure cannot be uniformly and adequately applied.

3. Former construction: Try not to necessitate the use of a former that is needlessly difficult to prepare or requires the use of expensive processes, such as use of a 5 axis CNC, unless the project calls for and warrants the complication.

4. Material usage: Aeroply and thin solid layers will bend in one direction only and layers of veneers should generally also be oriented with the same grain direction. So during the planning stage, it is good practice if you can plan how you will lay out out the material for cutting most efficiently.

5. Finishing the lamination: It is good to plan in advance how the lamination will be trimmed and treated after forming as this may cause you to change some details of the design.

Once the section is designed, the material can be prepared. When pre-cutting the layers, it is good to include an allowance, or shoulder, of 2-4mm around the entire layer. Glue can cause a little bit of slippage during glue up and this gives you enough of a “safety zone” to trim the final piece to size. Cut one extra layer of the aeroply with an extra shoulder of 4mm around all edges and set this aside.