Monday 9 July 2018
I was cramping up the underframe of a table with laminated stretcher rails; for some reason it was easier to do this upside-down. As I stood back to admire the table, I suddenly saw in the construction my next project – an exhibition piece – the outline shape for a desk. From that point on, I drew every detail of the construction out in full size on white-faced hardboard. So the drawings here are the first to be reduced to scale drawings – and there's no question which was easier!
Drawing the arcs
If you choose to make a desk based on this design you must first reverse the process and draw out a full-size plan view of the laminated stretcher rails onto a large board. I made large wooden compasses for this purpose, though trammel bars would also be satisfact-ory for drawing the arcs.
Six formers in all are needed for the construction of the desk: three for the underframe, one for the top-end rails, one for both the back rail and the drawer fronts, and one for the swivel drawers. The construction for each former is the same, and the one to shape the end stretcher rail is illustrated. The length – including the tenons – of the end rails is 700m (27 5/8in) so the former will need to be about 800m (31 5/8in) long. It is assembled from one piece of 6mm (1/4in) plywood or MDF, and four 18mm (23/32in) pieces of MDF, 800mm long and 200mm (8in) wide.
The pillar drill is set up to to drill two identical 12mm (1/2in) holes in each of the five pieces. The 6mm piece is cut to the finished inside shape of the stretcher rail. Using 12mm (1/2in) dowels for location, screw the 6mm template onto the first of the 18mm (23/32in) boards.
Bandsaw and router
Remove the bulk of the waste with the bandsaw and finish with a bearing-guided router cutter. This is best done on the router table but can be cut by hand-feeding the router against the template. Repeat for the other three pieces.
Using two longer pieces of 12mm (1/2in) dowel to locate all five pieces, glue and screw together. Sand the finished surface and polish to prevent the laminated rail sticking to the inside of the former. Alternatively, cover the surface with wide parcel tape. This is quicker but be prepared to repeat the process if you need to use the formers again.
There are many who advocate the use of a male and female former. This requires fewer cramps when gluing up and is good when the curves are shallow, as in the top rails. They will, however, need more care to ensure they match perfectly and you will need to use much more material.
Cutting and gluing laminated rails
A 300mm (approx 12in) saw blade with a 2.4mm (3/32in) kerf is used to cut the laminates. The stretcher rails each consist of six sawn laminates 80 by 2.3mm (3 1/8 by 3/32in) making a finished rail, 70 by 14mm (2 3/4 by 9/16in). The eight top-rail laminates are cut 110 by 2.5mm (4 1/4 by 3/32in) to make a finished rail 100 by 20mm (4 by 25/32in). It's only necessary for the outer laminate of the top rails to be of the 'show' timber but there's something reassuring in having the same material all the way through.
10 walnut (Juglans sp) laminates are cut for the desk drawers to make a finished thickness of 18mm (23/32in). The face veneer used is the crotch section of the plank as used for the top. I select the two outer surfaces for each rail, clean with a cabinet scraper, and sand before gluing. Glue is applied to both sides of the inner laminates. Cascamite or Aerolite is used throughout for the laminated rails. The gluing up table was in constant use for four days as two laminates were glued up each day! This is slow but safe, and there are plenty of other pieces to work on.
If you're only using one former it's vitally important to spread the pressure of the cramps evenly against the laminates.
A strip of plywood is used to cover the outer laminate and a cramping strip of 4mm (5/32in) cross-grained birch plywood is supported by cramping blocks. It's surprising how often this support band is used in this and other gluing operations!
Cleaning up the laminated rails
Cleaning up laminates that have been glued with any of the urea formaldehyde glues (Cascamite or Aerolite) is always a scary experience; one weeps for any sharp tool-edge that comes into contact with this glass-like glue. One solution is to use a wooden jack plane to prepare one surface to a reasonable degree of flatness and squareness. Then cut the laminate on the table saw as wide as possible, removing the other glued edge and leaving it flat, clean and square. The nail is then reversed and the planed edge sawn to width a little over the finished dimension. The square-sawn edge left from a tungsten-tipped blade needs little planing to finish.
This is the time when the full-size plan view of the table becomes so important. The four rails can be matched and cramped together to fit the drawing. The surface of the laminated rails that are to be joined need to be planed to perfect the butt joints. This will also reduce the combined thickness of the rails to about 26mm (13/64in). A little tension in the structure is acceptable as the glued areas are reasonably large.
Preparing the legs
The legs are cut and planed to 70 by 70mm (2 3/4 by 2 3/4in). The corners are cut off at 45 degrees leaving a minuscule amount to be planed to create a perfect octagon.
One mortice 56 by 12mm (2 1/4 by 1/2in) is cut in each leg for the combined stretcher rails, leaving a shoulder of about 7mm (1/4in full) at the top and bottom. The tenons can then be cut to fit the mortices.
After the stretcher frame is fitted to the legs they can be cramped together dry while the top rails are marked and jointed. It would have been nice to cut the mortices at right angles to one of the facets but this was not possible. A new shoulder-line and guide-line for the mortices is marked from a squaring jig or adjustable bevel that lines up the inside – or outside – of a pair of legs.
A cutting box is made to cut the new shoulder lines and the open mortices. Once the mortices have been cut, the frame is reassembled so the rails can be marked to length and cut to fit. The angles at which the various rails meet at the legs mean that gluing up could be problematic. Consequently, the mortices for these rails are open at the top in the manner of a bridle joint.
With the size of each leg and the density of the maple (Acer sp) there's little possibility the leg will split. The back and two end rails can be fitted in place before marking and cutting the front rails. The joints for the top front rails are a variation of the conventional desk construction, a full-thickness tenon in the lower rail into the leg and lap dovetails on the top rail. These rails are left parallel until the jointing has been completed. To simplify another possible problem, the inside front face of the end rails is planed flat. After fitting these joints, the front curve is marked from the laminated drawer front.
In part 2 (coming soon) Robert describes the making and fitting of the top, runners and the drawers.