Tuesday 28 October 2008
Mark Ripley makes an entertainment centre in cherry and walnut
This project is one of a number of pieces commissioned and discussed over recent years by people looking for attractive accommodation for televisions and hi-fi equipment. The latter seems to be shrinking steadily, while TVs just seem to get bigger and bigger. Large widescreens are often wall-mounted of course, which is of no interest to furniture makers, but can generate the need for small cabinets to house ancillary stuff, including DVD players, DVDs and accessories.
This piece was designed to house the TV behind bi-fold doors, an idea I have used before, but treated rather differently this time. Part of the object in the client's mind was to deliberately limit the size of television with which they could fit into a cabinet. This is also a commemorative piece, which is always a bit special for a maker.
TimberCherry was chosen for its warm colour, and the walnut to give a subtle contrast - I say subtle because when the cherry has darkened a bit, the colour difference will be less pronounced. I once made the mistake of inlaying some cherry drawer fronts with a dark mahogany; after some years, the colour difference is indistinguishable. The stringing gives definition to the proportions of the doors and gives a less abrupt break between the walnut door panels and cherry frames. A sense of lift is achieved with tapered sides and curved top rails.
I used a lot of American Cherry at one time. It used to be sold as straight edged boards, but the quality of stock offered seemed to deteriorate to the point where buying it became pointless, on account of the amount of sapwood present. I was sold some steam-dried cherry once, which seemed to be an effort to colour the sap wood so that we wouldn't notice it! Whatever they did seemed to effect it's gluing properties, and if it is still available anywhere, I wouldn't recommend it. Now though, American Cherry is being imported as through and through boards, with no more sap than we would expect in anything else. The timber I have bought has been very nice and came from WL West and Sons in 54mm (2 5/32in) boards, partly because there was no 27mm (1 5/64in) available when I wanted it, and partly because I wanted extra thickness to use for the ends.
The remaining stock was re-sawn for rails and doorframes, base and shelves. Incidentally, I would suggest buying 27mm boards and forgoing the re-sawing - I would if I did it again! It's a lot of work for the sake of bookmatched doorframes, and I was left with plenty of attractive off-cuts with no immediate application. It's in stick in the timber rack and will either end up as a small speculative piece, or a mandolin, but that's another story.
The walnut was the lovely, dark chocolate brown that black walnut is capable of.
DesignThe construction of the piece is uncompromising, with double through wedged mortise and tenons in the base to end joints, and lap dovetails in the top rails. Deep top and bottom rails are fitted at the back to help prevent racking. The piece is backless to allow easy access for cables and airflow, so the normal stiffening effect of the back is absent. The stringing is actually laminated; this is done before making the door frames, and is a simple way of creating the effect. It also has the attractive bi-product of replicating the detail on the back of the door. In use, the central doors are open and folded back onto the outer doors, and this feature is shown off to good advantage, especially if there's nothing on the TV worth looking at!
Timber selection makes use of the best of the figure in the top and ends. The door stiles are arranged to draw the eye to the centre. If possible, curved figure should follow the arched feature of the doors. A single piece is selected to run through all four doors, and the curve is to some extent, drawn to fit the figure in the wood.
The recessed handles are a gentle curve picking up on the arched doors. Designing a piece involves a decision on detailing. The object may appear sophisticated, but should be essentially simple, repeating one or two themes on different scales and generating overall harmony.
ConstructionThe construction is mostly traditional with through wedged mortise and tenons joining the base to the ends, and dovetailed rails at the top. Firstly, the parts must be prepared, including the tapered end panels. The more accurately the tapered pieces can be machined prior to assembly, the less planing and finishing there will be later. One of the safest and most predictable methods is to make a tapered jig to enable them to be thicknessed. Cherry can machine badly, especially against the grain, so make small incremental cuts. Biscuit jointing should ensure accurate glue up. Finally the faces of the panels are hand-planed and sanded, and the ends dimensioned.
Top, rails, base and dividers, are relatively straightforward. Mark out all the joints at the same time. The twin mortise and tenons are linked with a 6mm (1/4in) deep housing. As the mortises for wedged tenons are tapered and therefore wider outside than in, the internal dimension is 4mm (5/32in) narrower than the thickness of the base, allowing for a 2mm (5/64in) taper. Ideally, the finished mortise should be the same, or marginally less than the thickness of the base. This makes fitting the housing easier and also has a visual reason. If the tenons on the outside of the ends are wider than the thickness of the base, they will look wrong. On the subject of looking right, the wedges themselves should be the same size and exactly the same width as the tenon.
The trench for the housing was cut with a router, and the mortises with a mortiser, before the taper is cut in by hand with a mortise chisel. Begin cutting the base tenons/housing with routed rebates on each end. The tenons are bandsawn and the waste between the tenons is again removed with a router, with the fence running against the end of the base.
For the housing section of the joint, small bits will need to be left otherwise the router fence will have nothing to run against. These spurs are removed by hand.
As with drawer-making, the dovetails are marked and cut first, and the sockets scribed off them with a marking knife - I generally cut the dovetails on a bandsaw. The sockets are sawn by hand and the bulk of the waste is removed with a router, before the joint is finished by hand with a chisel.
AssemblyThe dividers are biscuit jointed to the base. Where the dividers meet the rails, they are screwed and glued; likewise, the base-to-base rail is screwed. The visible screw holes are plugged with 12mm (1/2in) pellets. The plinths are set into grooves routed into the base and ends. At the back, the plinth extends over the base, again adding stiffness to the structure.
All interior surfaces are finished before assembly, with two coats of thinned polyurethane, cut back between coats.
The sequence of assembly is:
1. Dividers to base
2. Ends to base
3. Base and top rails and plinth
PVA glues seem to be getting quicker at drying - either that or I am slowing down! The down side is that 'open time' is reduced, which can be an issue with complicated glue ups. I read a boat-building magazine where a builder was advocating 'wetting out' both mating surfaces with glue applied with a brush - which I do - and letting the glue go off slightly before clamping them together - which I don't, at least no more than I can help. One reason for pre-finishing interior surfaces before assembly is that it makes removing dried excess glue much easier; another is that it is difficult to get a good result when finishing into corners. After assembly, the piece can be trued up. Special care needs to be taken to ensure that the front is flat.
Shelves and topThe shelves are made and dimensioned. Dowel shelf supports are fitted for the side shelves, and allow three shelf positions.
As walnut was used as a contrasting feature on this project, this is what was used to turn the shelf supports. The central shelf is for a television and needs more substantial support, so screwed blocks are fitted here. They are too low down to be visible so their chunky appearance is not a major issue.
Screw blocks are also used to fit the top in the centre of the dividers and ends, otherwise the top is screwed through the front and back rails.
FinishingCherry, as is noted in books on timber, "takes a high polish". It does, but it makes you work for it! Sanding down through the grits to 150 silicon carbide on a Random Orbit Sander, produced a good surface, which was further hand-sanded. I generally check sanded surfaces with a magnifying glass and low angle spotlight - low angle sunlight is best. The time this takes is marginal compared with that of having to refinish a surface.
A thinned polyurethane sanding sealer was applied in two coats with a cloth, and cut back with a palm sander, prior to applying Danish oil. Initial coats were applied with a cloth and later ones with synthetic wire wool. If anything, the problem is preventing too high a finish developing, and I used a medium grade applicator.