Weekend Projects - Ash bowls archive

Friday 27 May 2016

In the latest part of his series on local timbers, Bob Chapman looks at one of the most common species in Britain – the ash tree

Gallery

While my wife and I were on holiday in Dorset on the south coast of England, in June 2009, I heard about an ancient ash (Fraxinus excelsior) tree in private grounds in nearby Somerset and I am indebted to the owner for letting me see, and take photographs of it. It is thought to be the oldest ash tree in England and possibly in the whole of the British Isles. Its immense girth, around 9 metres, testifies to its great age, which has been estimated at somewhere between 250 and 500 years. Even at 250 years it would be very old for an ash tree, and at 500 it would be ancient indeed. Whatever its age, it is obviously a dignified great-grandmother of a tree and looks as though it has spread its skirts and settled down to a well earned rest. Superb in its parkland setting, its gnarled and twisted limbs are supported on wooden blocks and despite its contortions and the damage that its great age makes inevitable, there’s no doubt that it is receiving good care in its dotage.

Ash is one of Britain’s most common trees and excellent, though less venerable, examples are to be found everywhere. A short walk from my home in Bingley in West Yorkshire, much further north than Dorset, this fine ash tree has, for many years, offered shade to the barges toiling up the flight of locks on the Leeds-Liverpool canal. A little further afield, in the Yorkshire Dales, a smaller example clings for dear life to a rocky outcrop. Its precarious position has caused its growth to be stunted but it is a good illustration of the tenacity and toughness of the species.

Ash timber is best known for being tough and resilient, and ash was once the most economically valuable of all European trees. Its timber has many uses and it is widely used for any application where strength and resistance to shock are needed, most commonly in handles for tools, such as axes, hammers, picks, spades and so on. It has also found use for making snooker and pool cues, baseball bats, hockey sticks, bows and skis, which must all withstand collision or bending forces without fracturing. Ash was used in the chassis frames of Morgan cars, and in the construction of the de Havilland Mosquito fighter bomber of World War II, the so-called ‘wooden wonder’.

The grain and figure of ash can be very attractive, especially in ‘olive ash’, which is not a distinct species but is so called because its darker colour and contorted figure resemble that of olive wood. Ash is now finding wider use as a decorative timber for turning and for furniture making, as well as for shop and office fittings.

Ash bowls

While demonstrating at the North of England Woodworking Show at Harrogate in 2009, I found some squares of ash that had a beautiful ripple figure. They were not cheap, but, I thought, worth the money. The wood is beautiful and turned very easily. The first decision I had to make was whether to turn a single bowl out of the piece or cut it up and make a number of smaller bowls. The square was 260 × 260 × 50mm-thick and although these are reasonable dimensions for a bowl, by cutting it in half both ways I would end up with four pieces whose thickness was deeper in proportion to their maximum diameter, and that is what I decided to do. Should I make a set of four identical bowls or make four different ones?

Making four identical objects, no matter what they are, is never easy, whereas four different designs give plenty of scope to experiment. After a few minutes spent sketching possible designs, I decided that four different bowls would be far less demanding and far more interesting. I sketched a couple of full-size profiles roughly on the side of the square to double check how they might fit. They were approximately 130 × 50mm. This helped me realise a small oversight, which I will come back to a little later. Each of the four bowls was made in much the same way. What follows is a description of making the bowl design shown at the bottom of the diagram, but it applies equally well to the others.

Chuck screws

As supplied, most screws are much longer than mine and if used ‘as is’ they may be inconveniently long. No matter what length the screw is, it will dictate the minimum depth of the bowl, which must be hollowed at least as far as the bottom of the screw hole. A longer screw obviously requires a deeper hole and this will demand a thicker piece of wood, or the use of spacers to take up the length of the screw. Spacers move the workpiece further from the support of the headstock, increasing the risk of vibration. If you have more than one of these chuck screws, then cut them to different lengths to suit different workpieces.

Tools used:

3mm parting tool

20mm skew chisel

6mm bowl gouge

13mm bowl gouge

25mm round-nose scraper

Screw chuck

Abrasives down to 400 grit

Beeswax

Carnauba wax

Vacuum chuck – if you have one

PPE: facemask, respirator/dust mask and extraction

STEP 1

Cut the square into four pieces and drill an 8mm hole approximately 25mm deep in the centre of each one to accommodate the large screw that fits in the chuck. Most chucks are supplied with a screw like this and the hole size may need to be changed to suit your particular screw. The assembly is commonly called a ‘screw chuck’

STEP 2

Usually I begin by mounting the blank on the screw, truing up the blank and forming a spigot to hold it by when it is reversed for hollowing. However, in this case, I wanted to incorporate the whole thickness of the ash into the bowl shape, and not waste any forming a spigot. This was the oversight, and to overcome it, some small blocks of scrap wood were glued to the underside of the bowl blanks using a good quality adhesive. The spigots could then be formed in this scrap wood leaving the whole thickness of the ash for the bowl

STEP 3

With the bowl blank screwed securely onto the screw chuck, true up the sides of the blank with a 13mm bowl gouge. Mark the centre of the blank by bringing up the tailstock centre and winding the point into the wood

STEP 4

After marking your diameter, use a 3mm parting tool to cut a groove to the required depth in the scrap block. This should be a little less than the maximum depth of the jaws so that the spigot will have maximum strength but will not ‘bottom’ in the jaws. Use a small bowl gouge to remove the corners of the scrap block and turn it to round. Remove the waste down to the level of the ash blank

STEP 5

In order to make the diameter of the foot about one-third of the diameter of the bowl, a little more of the scrap block has to be removed before cutting into the ash with the parting tool and removing the waste with the bowl gouge. This is continued until the foot of the bowl has been roughly formed

STEP 6

Using the 13mm bowl gouge, remove waste wood between the foot and the rim of the bowl. Aim for a smooth curve with no bumps, hollows or sudden changes of direction

STEP 7

With the underside of the bowl shaped, use a 3mm bead forming tool to cut a series of decorative beads across it. Start at the corner where the bowl meets the foot and work outwards so that any ‘part beads’ will occur in places where they can be turned away later

STEP 8

Using abrasive, gently sand between and over the beads, taking care not to flatten them. Work down to about 400 grit. Brush on sanding sealer and, when dry, sand lightly with the 400 grit paper. Polish the bowl by rubbing it over with a stick of beeswax followed by carnauba wax. Do not overdo the waxing and don’t let the wax accumulate in the grooves

STEP 9

Reverse the bowl in the chuck and true the front face up with a bowl gouge. If there is a ‘part bead’, cut it back to the next full bead. Decide on the wall thickness and use the point of a skew chisel to form a small ‘starter groove’ for the bowl gouge. Holding the gouge on its side, push the tip into the starter groove immediately and, still pushing gently forward, rotate the gouge anticlockwise to bring the flute to the 2 o’clock position, and swing the handle slowly back towards the body. These actions cause the cutting edge of the tool to curve forwards and towards the centre, removing wood and starting to hollow the bowl. Keep the bevel of the gouge in contact with the freshly cut surface, otherwise you’ll lose control of the direction and depth of cut

STEP 10

While the walls are still reasonably thick and strong, finish the rim of the bowl by converting it to a slight curve using the skew chisel on its side, flat on the rest as a scraper. Use a small 6mm scraper to undercut the rim slightly. This tool has had the usual burr honed off on an oilstone, and the cutting edge is sharp. Hold the tool horizontally, flat on the toolrest with the cutting edge exactly at centre height. Take fine shavings until the depth of the undercut is satisfactory

STEP 11

With the undercut completed, take the central lump down in stages. Check the wall thickness frequently to ensure it is fairly constant although some thickening towards the base is acceptable. When hollowing with the gouge is completed, remove any ridges in the surface with a 25mm scraper. Again, the scraper is honed and is used horizontally, then sand, seal and wax the inside of the bowl as before

STEP 12

One way in which the bowl may be held in order to remove the spigot is by a process known as ‘reverse-chucking’. Use the tailstock centre to push it against a rubber-faced drive plate, centring the bowl using the centre mark formed much earlier

STEP 13

With the tailstock in place the bulk of the spigot and most of the scrap block can be removed. When as much wood as possible has been turned away, the bowl may be removed from the lathe and the final stub removed with a sharp knife. The bottom of the bowl can then be hand-sanded and polished

STEP 14

However, as I have a vacuum system I was able to hold the bowl in place while removing the tailstock altogether, and I finished the bottom of the bowl with a small bowl gouge, sanding and polishing as before

STEP 15

A collection of four small ash bowls, each approximately 130mm diameter × 50mm deep. These different designs were made from the same piece of wood; the one described here is on the extreme right


Briony Darnley

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Bob Chapman , Weekend Projects