Night at the Opera archive

Monday 9 January 2012

Bob Chapman makes this unusual sculptural piece which was influenced by the Tenerife Opera House

Gallery

A few years ago my wife and I embarked on a cruise, and one rather dull afternoon we found ourselves marooned in Santa Cruz, the capital of Tenerife. With little else to do we decided on a stroll along the seafront where, after about a mile, we happened to arrive at the 'Auditorio de Tenerife', the Tenerife Opera House. Wow! The building is quite stunning. Its most striking feature is a beautiful pointed 'roof' which arches over the entire structure.

The opera house provided the inspiration for the piece I called 'A Night at the Opera.' During the 'critique' at the AWGB seminar in 2009, Bert Marsh described this as "The piece I would like to take home with me," and in a private conversation afterwards he told me again how much he liked it. Praise indeed.

Tools used: Narrow parting tool, captive ring tool, skew chisel and 13mm (1/2in) bowl gouge

Step 1

My first thought was to cut two opposite sides from the bowl and then glue them together, but I soon realised that I needed to cut a circular 'slice', at an angle, from the bottom of a bowl

Step 2

I calculated that the diameter of the circular slice needed to be approximately 80% of the diameter of the bowl. For a bowl 150mm (6in) diameter the slice should be 120mm (4 3/4in) diameter

Step 3

Mount a piece of beech 35mm (1 3/8in) thick and 150mm (6in) diameter on a screw chuck. True up the piece with a 13mm (1/2in) bowl gouge and form a chucking spigot on the underside by removing waste with the bowl gouge and then forming the dovetail shape with the long point of a skew. The size of the bowl is not critical, but I recommend a diameter of around 125 to 150mm (5 to 6in) to start with. Don't make the bowl too deep, as the depth will be more or less doubled in the finished piece

Step 4

Leaving a small section flat around the spigot will help seat the chuck jaws securely later. Use the bowl gouge to shape the underside of the bowl into a smooth curve up to the rim. Sand from 120 down to 400 grit. If you intend to bleach the wood, then leave it unsealed, otherwise seal and polish

Step 5

Use the toolrest to mark a line across the bowl surface from one side to the other. This should align with the grain direction to avoid forming narrow sections later on which have the grain running across them. With this line marked, the blank can be removed from the screw

Step 6

With the dovetailed spigot held securely in the chuck jaws, hollow the bowl to a wall thickness of around 5mm (3/16in) using a 13mm (1/2in) bowl gouge. Sand down to 400 grit, and leave unsealed if bleaching it. An even wall thickness is not essential, and you don't need to bother too much about the centre of the bowl because it will be removed when the 'slice' is cut away

Step 7

Once the bowl is made, mark the slice out on the underside by setting compasses to 60mm (2 3/8in). The centre of the circular slice must lie on the pencil line drawn earlier. By trial and error find the centre of a circle that comes close to the edge of the bowl. This circle is the circumference of the slice. In order to cut the slice off the bottom of the bowl a special 'carrier' must be constructed to hold it at the correct angle. Hinge two plywood squares, a little larger than the bowl diameter, together along one edge. Fix a sliding clamp on an adjacent edge, near to the opposite side

Step 8

Mark a horizontal line across the carrier and align the line across the bowl with it. Glue the bowl to the carrier using five or six dabs of hot melt glue around the rim. The circles drawn on the carrier are from a previous job and are irrelevant to this project

Step 9

Adjust the angle of the carrier so that the bandsaw blade will cut the bowl at the correct angle to remove the slice. This is most easily done by a little trial and error. Line the front of the cut up with the front of the blade...

Step 10

...and line up the back of the cut with the back of the blade. Continue the adjustment until both ends of the cut are correct, then lock the carrier in place by tightening the screws in the sliding clamp

Step 11

When all is correct, the slice can be carefully cut from the bowl. Keep the carrier tight to the saw fence and guide the bowl gently by hand, keeping fingers well away from the blade. Owing to the shape of the bowl, it is not easy to use a push stick for this

Step 12

With the slice removed take the 'bowl' off the carrier by warming the glue, and then cut in half along the remaining pencil mark

Step 13

Apply a thin coat of PVA adhesive to the cut surfaces. I find a finger is by far the easiest tool for this job. Avoid using too much glue as it can be difficult to remove 'squeeze out' in the valley formed between the two pieces. Line up the tips of the two pieces and hold them with a clothes peg. Align the curved edges and clamp the wide end with a rubber band. Leave overnight for the glue to set

Step 14

Clean up and level the wide end of the assembly on a sanding disc. By holding the tip about half an inch from the disc surface, sand the wide end at a slight angle. This ensures that when the wide end is eventually fastened to a base, the pointed end will stand above the surface

Step 15

Using a drum sander in the drill press, sand the inside curve smooth, taking care to maintain an even curve from tip to base. Sand away more near the tip to thin it and make it more elegant. At this stage you need to bleach the piece to make it paler in colour. I've used Rustin's two part wood bleach several times and find it does exactly what it claims. Simply follow the instructions given on the box. The bleaching will raise the grain slightly and, when dry, it can be rubbed down with fine steel wool to restore the smooth surface. You can then apply two coats of cellulose sanding sealer as the final finish, rubbing down between coats

Step 16

Measure the distance from the upper surface of the tip to the bottom of the valley at the wide end. Add 5Mm (3/16in) to this measurement. This value is the internal diameter of the partial ring which will form the 'spine'

Step 17

Next, you need to mount a piece of scrap wood on the screw and, after marking the required internal diameter, use a captive ring tool to form a ring of the correct size. Sand the ring smooth while it is still attached. Don't part all the way through at the back because when the ring comes loose it will be trapped between the wood, the tool and the toolrest, and will almost always get broken. Instead, move the toolrest to the front of the piece and use a narrow parting tool to part off the ring while catching it with the left hand. This method has proved very effective in making unbroken rings of all sizes. The ring will inevitably have a residual narrow fillet on the side but this is easily sanded away

Step 18

Place the ring around the piece and mark the required length, allowing an extra 13mm (1/2in) or so. Cut the required segment out of the ring and sand one end down to a rounded point. Sand the outside curve down towards the inside, starting far enough back from the tip to make the change in direction of the outer curve imperceptible. In a similar way, sand the sides in towards the point

Step 19

Drill a hole in a piece of scrap, big enough to put the end into to hold it, and spray the curved segment matt black. At the same time, prepare a rectangular base from whatever you might have - I used plywood - and spray that too. I made a small painting stand for the base by knocking three nails through a piece of scrap

Step 20

When the paint is dry glue the curved segment in place to form the spine of the piece. If you have used cellulose paint, as I have, do NOT try to glue the spine in place with CA adhesive - it dissolves the paint instantly and it will get everywhere. Using three or four tiny dabs of an epoxy glue is much safer. Use clothes pegs to clamp the spine in place. Align the tips and sand off the excess spine at the bottom when the glue has set. Drill suitably sized dowel holes in the bottom edge of the piece. I find this is best done by switching the drill on and, holding the piece by hand, pushing it upwards onto the drill. It is not necessary to go deeper than 4-5mm (about 3/16in). Take care not to come through the sides of the piece. A cocktail stick or matchstick makes good dowels for this purpose

Step 21

Put a tiny dab of white correction fluid, or any white paint-like liquid, on the ends of the dowels and touch these onto the base where you want to position the piece. The resulting white spots enable you to drill the dowel holes in exactly the right places. With the piece glued to the base the sculpture is finished. In the original piece I made two arches, of different sizes, but the technique is identical for both. Obviously a bigger base would be required

Step 22

In this instance I decided to add a bleached beech ball to give a focus and add interest to the piece. The ball is dowelled to the base in the same way as the main piece

(PHOTOGRAPHS BY BOB CHAPMAN)


Woodworkers Institute

Tagged In:

Woodturning , Bob Chapman , sculptural , Tenerife Opera House

About The Author

After teaching chemistry for many years, Bob took early retirement to become a professional woodturner, and is a member of the Register of Professional Turners (RPT). He was a demonstrator at the 2009 AWGB Woodturning Seminar and is available for lessons, demonstrations and commissions. Bob may be contacted through his website.
Email: bob@bobchapman.co.uk

The Tenerife Opera House - where Bob got the inspiration for this project

Diagrams Click an image to enlarge