How to Laminate
Tuesday 09 February 2010
Laminating is a portal to another dimension of furniture design and manufacture, although still in its infancy in the history of furniture making. Its origins date back only to the 1930s with designers such as Alvar Aalto whose designs must have shocked the largely Arts and Crafts-based woodworking fraternity.
Laminating has come a long way since then and can now be done without huge expensive machinery since relatively cheap vacuum bag presses have opened up the technique to the small workshop and the serious amateur. Here I am looking at a few techniques used in my own workshop that I hope you will find helpful.
A sturdy former is the first thing we will tackle. At my workshop we use two different types.
On smaller items a solid MDF former is constructed. This is ideal if weight is not an issue as it is very strong and will not deform around the edges.
On larger items where such a former would be heavy, we use blue extruded polystyrene. This should not be confused with expanded polystyrene which is white, much softer and is usually found in electrical appliance packing.
A full-size template is required to start making your former, and I make this out of 6mm MDF because it is quick to shape and wide enough to run a bearing-guided router cutter against it.
This will become your master template and should only be used once to achieve the first section of the former after which each piece is machined from this and not the master template.
Rough-cut the MDF using a bandsaw if you have one or a jigsaw if you do not. The MDF can be either glued together or double-sided tape can be used for a less permanent structure.
The blue polystyrene can be cut and either machined or shaped by hand but either way you must be aware of the dust created. The polystyrene must be mounted on a base of 18mm MDF or ply. This is not necessary on the solid MDF former.
A layer of 1.5mm 3-ply - also known as skin ply or Aeroply - goes onto the top of the former so remember to calculate the thickness into the dimension of the former.
This can be stuck to the foam using double-sided tape. Parcel tape is used to pull it all together and act as a non-stick surface.
Some spring-back on the laminated component is to be expected, depending on what substrate and glue are used. If required the former can be constructed to compensate for this, but trial and error prevails here.
Substrates and lamina
I have experimented with most options for substrates and they all have advantages and disadvantages. Flexi ply is available in many thicknesses, allowing almost infinite combinations that will amount to your desired finished size. I always use the rule of ply and have an odd number of lamina - this means the outside laminates are in balance with an equal number of glue lines.
Flexi ply has a very open grain and this can telegraph through the veneered surface. It is also quite susceptible to moisture and can change shape after laminating.
Layers of skin ply can be used as a substrate but this is expensive and the ply does not bend well when many layers are used.
MDF at 2mm thickness is very good but stiff when many layers are used. It is, however, very cheap, not susceptible to moisture after laminating and is very stable.
Solid timber lamina are cut on the bandsaw and then planed by hand or through the planer/thicknesser. Two millimetre lamina are ideal but care must be taken with timber species and thickness of lamina as all species have different bend characteristics.
Knife-cut veneer is a great lamina. Use sequential packs if you wish to see the edge, but it is the most expensive. Take care with glue lines showing on the joins, choose your glue carefully and where possible match the colour of cured glue to the colour of your wood.
Marking out, former and substrates
With any curved work it is imperative that clear datum marks are drafted onto the former and the material being laminated. If this is neglected at this stage then it is almost impossible to achieve any level of accuracy later on.
You need to mark a centre line across the former and over the lamination, and also across both ends with the angles these will be cut to. There are occasions when I use the former as a jig for machining processes later on and sometimes this will be sacrificing the former.
The key to success really is correct marking out before it comes off the former.
Trimming up laminated shape
After the laminated shape has set hard it can be removed from the former, having first ensured that the datum marks are clearly visible on the shape.
I use the surface planer on one side to flatten and square up to the face. You can do this with hand tools but cutting through a large glue area quickly dulls the blade. You can equip your planer with TCT blades for this kind of work. While they do not give the best finish they do last a lot longer and are about the only thing that will plane teak without being eaten alive.
Ends can then be cut on the bandsaw, tablesaw or routed to the desired angle. The other side can be rough planed close to a parallel line marked to the dimension required. I usually hand plane the final part to ensure complete accuracy.
If you are veneering the surface then the component can be veneered and re-pressed in the vacuum bag on the existing former. Trim shape to size and apply any lipping first before veneering.
Using hand tools or a bearing-guided cutter in a router table, trim the veneer after the glue has cured. Job done.