Stylised Seed Pod
Tuesday 25 January 2011
Bob Chapman creates this unusual stylised seed pod from a piece of ash complete with 'spikes' made from ebony, which makes a perfect ornament for any surface
Nature is incredibly inventive and seeds and seedpods are a terrific source of inspiration for shapes and textures. They can vary from the extreme spikiness of the teasel to the almost perfectly spherical peppercorn. They may show wonderful symmetry like the star anise or a poppy seed head, and they may fall naturally into two halves like the garden pea, a pistachio or a walnut. This piece stems from that very inspiration.
Sketching a number of imaginary seed pod-type shapes eventually led me to the design adopted here.
The dimensions shown on the drawing opposite are not critical but there are other design criteria to take into account. When the bowl is cut and re-joined, the shape formed where the rims meet becomes one of the focal points of the piece. It is well worth sketching different rim shapes to plan this effect in advance. Undercutting the rim slightly has a marked effect on the elegance of the finished piece. Do not make the bowl too deep - the depth will be doubled when it is cut and re-joined - and it is easy to spoil the proportions of the final shape.
Tools used: 13mm (1/2in) bowl gouge with single bevel, 13mm (1/2in) bowl gouge with multiple bevel, 6mm (1/4in) scraper and 25mm (1in) skew chisel
For this project you will need a piece of ash (Fraxinus excelsior) which measures a little more than 150mm (6in) diameter and about 50mm (2in) thick
Mount the blank on a screw and true up both faces, removing material from the faces until the thickness is reduced to about 40mm (1 5/8in). This allows for a spigot to be formed, which will be removed
Mark out the depth of the rim features on the side of the blank with a pencil and, with a 13mm (1/2in) bowl gouge, shape the underside into a smooth, flowing ogee from the spigot to the rim. Finish it with a fine cut, but don't worry about sanding at this stage
Attach a piece of wood to the toolrest to act as a drill guide, and mark the required depth on the drill bit. 7mm (9/32in) might seem an odd drill size to choose, but I found by trial and error that 6mm (1/4in) holes seemed just a little too small for the proportions of the piece, and I then re-drilled them all a little larger. It's surprising what a difference that extra millimetre can make! Use the lathe's indexing system to drill 24 holes, evenly spaced around the circumference, about 6mm (1/4in) from the edge and 6mm (1/4in) deep
Reverse the blank in the chuck and mark out the size and positions of the rim features, working from the designs you have already made
Begin hollowing the bowl, but only enough to distinguish the rim, without weakening it. I then used what I call a 6mm (1/4in) 'flat gouge' to shape the curves into the rim area. The flat gouge is, essentially a scraper with the burr honed off, used angled slightly upwards as you would use a gouge. It leaves a fine finish which doesn't need sanding
The upper surface of the rim must remain perfectly flat, as this will form the mating surfaces when the bowl is cut and re-joined. Pencil over the relevant surface to make it show more clearly. Use a straight edge to check it is level and adjust as necessary
The flat gouge, now functioning as a scraper, is used to undercut the rim of the bowl. Adjust the toolrest so that the cutting edge of the tool is at centre height with the tool held horizontally. Take fine cuts, deepening and widening the undercut to the finished shape
With the undercut done, complete the hollowing of the rest of the bowl with a 13mm (1/2in) bowl gouge. To achieve a smooth curve and a level surface be sure to keep the tool's bevel in contact with the wood, and the flute at about 2 o'clock
As hollowing proceeds, check the bowl's wall thickness frequently. When the bowl is cut in half, the wall thickness will become visible. The actual thickness is not important, but it is essential that the wall is an even thickness. If it varies in thickness, especially if there is a bump or a hollow in the middle, it will spoil the whole look of the piece. When all is right, sand and finish the surface with cellulose sanding sealer. I did not apply any other finish on top of the sealer
I reversed the bowl by expanding the chuck jaws of my large Vicmarc chuck into the bowl, aided by the undercut of the rim which helped locate the jaws firmly. If your chuck will not expand far enough you might use button jaws or a jam chuck or mount the bowl between a rubber-faced drive plate and the tailstock centre. Carefully remove the spigot with the bowl gouge
It is essential that the bottom of the bowl runs from one side to the other in a single flowing curve. If you want a smooth finish to your work now is the time to sand and polish the underside. Sand and finish with sanding sealer. Carefully cut the bowl in half on the bandsaw, and glue the two halves together. Use Titebond II, spreading it very thinly on both surfaces using your forefinger. The mating surfaces are then rubbed gently together, positioned carefully and left overnight for the glue to set. Too much glue will result in squeeze out, which will be difficult to get at to remove. Better to be miserly with the glue in the first place. Do not attempt to clamp the two halves together as it will almost certainly cause them to move. When the glue is finally dry, carefully sand the sawn edges smooth and level off on a disc sander
Using a carbide burr in a Dremel, the holes are chamfered and then hand sanded to a smooth curve. I wanted to create the impression that the points were growing out of the form, rather than having been implanted into it
The points are made of ebony (Diospyros spp) 25mm (1in) long and 7mm (9/32in) diameter. After reducing the diameter and roughly shaping them with a bowl gouge, refine the points with a skew chisel used on its side as a scraper. I resist all attempts to tell me that this is a misuse of the tool. It isn't, because it's safe and it works. It is an alternative use of the tool
Glue the points into the holes with small beads of Cyanoacrylate adhesive. Again, it is better to be parsimonious to begin with rather than having to remove excess glue later. Texture the sides of the piece using the same carbide cutter in the Dremel. On reflection this might have been better done before inserting the points, but I was eager to see what they looked like!
The texturing raises small splinters and wispy bits of 'fuzz' on the wood, and these Scotch Brite radial bristle discs, used with a Dremel, are ideal for removing them. Give the textured surface a coat of sanding sealer, and then you're finished