The Technique of FURNITURE MAKING
Treatment of edges
All edges should be eased back to prevent lifting and possible impact damage (29:3). If the edges of the groundwork/substrate are also covered they should be laid first, trimmed off flush and the top applied (29:4), the front bevel being formed with a fine-cut file. Mitred edges (29:5) are possible but hardly sensible, as the resultant sharp corners positively invite impact damage, and a more satisfactory treatment is shown in 29:6. Other treatments are shown in 29:7, 8 and 9, and where hardwood lippings or edges are used they can be glued on first and the top cut to exact size and laid afterwards, or the top laid first and then the hardwood edge. Either method calls for skilful working, for the edges must be worked flush with the laminate, and the easier way is to glue on the edge and work it down to the exact projection to receive the laminate, using a loose waste strip as guide. Any fractional adjustment necessary after the top has been laid can then be done by protecting the top with a strip of cellulose tape, and sanding down the high spots. If the top is laid first and the edging after, then a slight bevel (29:9) will keep the cutting tool away from the laminate. Treatment for sinks, washbasins, etc. is shown in 29:10, where a fairly wide edge (A) is applied in case there is any water seepage which might delaminate the plywood layers, with a proprietary mastic bedding (B) between the edge and the rim of the sink.
Gluing procedures
Several types of gap-filling rubber-based impact glues are available for hand gluing, which only require moderate pressure as they give a powerful and immediate tack. They set by evaporation or absorption of the spirit solvent, and do not attain maximum strength for at least 14 days. An advantage of this type is that they retain a certain measure of elasticity, and will thus withstand fractional movements of the base. They are, however, only heat resistant to about 140° F (60° C) and although damp proof will not stand continuous moist conditions.
In using this type of adhesive over large areas speed is essential. The groundwork/substrate must be perfectly level, dust free and free from grease, etc., while spreading with gauged metal spreader, wooden squeegee or roller should be reasonably full and even, with both surfaces coated and allowed to air dry until the glue is tacky and no longer moist. The coated sheet must be carefully positioned, dropped into place, rolled or banged down with the clenched fist to expel any trapped air, and if pre-cut to exact size then a useful precaution is to tack temporary battens to the groundwork, and use these as locating shoulders. Any spilled glue should be cleaned off with a suitable solvent— petrol, cellulose thinners, etc.—or allowed to tack off and be rolled up with the finger-tips, while rollers should be cleaned immediately. If any edge tends to lift it should be clamped down, and the assembly left for some hours before further working.
Plastic laminates can be glued with gap-filling synthetic resin glues, and this is the standard production method, although clamping pressures are necessary. One of the best glues for this purpose is Aerolite 306 with GUX hardener in which a proportion of glycerine has been added to the hardener to impart a measure of flexibility. Application is the same as for wood veneering (Chapter 32), but hot pressing should not exceed 160° F (71° C) with pressures only sufficient to bring both surfaces into intimate contact, and not exceeding 40 lb per sq. in (2.812 gf/cm2). This method is preferable to hand gluing with impact glues which are more suitable for on-site work, for with clamping pressures the surface will be flatter, and the glue film will be both heat and damp resistant within the limits set by the laminate itself and the groundwork/substrate.
Bending
The standard 1/16 in (1.5 mm) veneer can be cold bent to simple curves of not less than 8 in (203 mm) radius, although narrow strips will probably follow a tighter curve without fracturing. The curve should be cut very full in the length with sufficient overhang to follow the sweep, and the waste trimmed off afterwards. For more acute curves either the standard laminate must be heat softened up to but not exceeding 302° F (150° C) which is just short of the blistering point, and clamped between formers/forms, or for very acute curves to a maximum of about 1 in (25 mm) radius special post-forming grades should be used (29:11). Most manufacturers issue their own data sheets for post-forming operations, and the schedules recommended should be closely followed.
