I have made several of these, and they are not complicated to make, but they do need a fair degree of tool control, and some courage, as for the latter parts of the turning, high speed is required.
- One perfectly square bowl blank. Even thickness is not a must, but the sides have to form a perfect square.
- Faceplate and chuck with dovetail or gripper jaws
- Irish grind bowl gouge (or similar), any size
- Round nose scraper or adjustable tip scraper (better)
- 3/8″ spindle gouge
- Skew chisel
- Drill chuck with a taper to fit your head stock
- Sanding arbor with hook pad, 1″ or 2″
- Velcro backed sanding paper (or abranet) 80 – 400
- Finish of choice (lemon oil for me)
And here’s how it’s done: Start out by finding the precise center of the square blank (and for this the blank really has to be square). Then mark the center with two black lines and drew a circle around it, using a compass with a pencil attached, exactly at the radius where the wholes in one of my faceplates are located. Next mark the positions of the holes on the circle and drill 2mm holes (on softer wood this isn’t needed). Finally screw the faceplate into these holes.
Now the whole thing is mounted directly onto the thread of the headstock. The first thing is to just clean up the underside. Next make a chucking point for expansion mode chucking, using a spindle gouge to take out the bulk of the material and then a half inch round bar skew chisel (in scraper mode) to create a slight recess for the dovetail jaws. This part then gets sanded and decorated with three little rings.
Now the bulk of the material is removed from the underside of the bowl. This is done with pull cuts using a bowl gouge with a long wing grind. Use a fairly high speed for this (not strictly necessary, because the blank still has quite a bit of material left on it and doesn’t flex yet). At this stage it is important to remember that two corners will face down, and therefore the smooth flow for this part of the shape has to be achieved. This final shape also requires that at the centres of all four sides the cut should be almost perpendicular to the lathe axis, more about this later. In order to get a decent finish before sanding, the final cuts on the corners should be push cuts, as they are going downhill, and therefore with the grain. Once happy with the shape, sand it to 400 grit.
Now the assembly is removed from the lathe, and the faceplate taken off. The blank is then mounted in expansion mode onto the chuck. The jaws must be clear of any dust, shavings and possible dents, to ensure a perfect seat. Any slight misalignment here will show multiplied by 2 or 3 at the corners.
Now the shaping of the bowl inside begins. Since the final wall thickness is meant to be around 1/8″, and wood becomes quite flexible at this thickness, it is necessary to turn the inside at high speed. I usually work at around 2500 rpm.
The inside is done almost completely with push cuts, using a bowl gouge. Again, the two rising corners define the shape of the cut, thus leaving (for now) all 4 corners substantially thicker than the rest of the bowl.
Start with heavy cuts to remove the bulk, but leave the centre of the bowl quite strong. Once the wings are down to about 1/2″ thickness, the tricky bit begins. Depending on the choice of wood, it will sooner or later start to flex. This can be counter acted by turning at high speed, but only to some degree. In consequence the final thickness has to be achieved in small increments, working from the outside towards the centre.
With the flute almost closed, feel for the bevel to make contact with the wood, then pull the gouge outwards along the shape, adjust the cutting depth and move in. As soon as you have cut a few millimetres, open the flute and ride the bevel along the shape for about 1/2″. Repeat this until you have achieved final wall thickness. Then repeat the entire procedure with the next 1/2″, and so on, until you are cutting continuously. From there on the rest can be turned as usual. But never forget that the 4 corners must have the drooping shape on the underside and the rising shape on the inside.
Once you have even wall thickness and a nicely flowing shape for the inside, smoothen out any cut marks with the scraper of choice and begin to sand. Obviously you can only sand those parts where material is supporting the paper in a circle, i.e. the corners need to be sanded by hand.
However, the corners are not done yet. For this, remove the bowl from the chuck, and remove the chuck from the lathe, replacing it with the drill chuck. In order to remove the bulk of the excess material in the corners, I usually use a drum type Saburr Tooth Carbide Sanding Sleeve, but other methods are also suitable. The sleeve fits onto a mandrel that can be mounted in the drill chuck. Run it at the highest speed your lathe will give, and carefully remove the wood by holding the bowl against the sanding sleeve. You must wear some kind of face mask and breathing kit for this, as the waste will go everywhere. Also, be careful, the Saburr Tooth will remove lots of material very rapidly.
The important thing to aim for is consistent wall thickness in the profile. This can only be achieved, if the center portions of the bowl walls are cut almost at a right angle, otherwise the picture gets distorted and in order to achieve a consistent visible thickness you’ll end up with an varying actual thickness.
Once the corners are roughly in the required shape, replace the sanding mandrel with the sanding arbor, and start working your way through the grits.
Towards the end I usually work with a random orbit sander, with a soft pad on the sander and then 600 or 800 grit paper on top, just to achieve a smooth surface. At this stage it also usually pays to use compressed air to get rid of dust. This will reveal any slight scratches. It is also absolutely necessary on open grain woods, as otherwise the dust will collect in the open grain, and this will affect the final surface of the piece.
Open grained woods should be finished with oil, as to preserve the open grain. Closed grained woods can have any finish you like. Alternatively you could also brush out the open grain, spray paint and then apply a limed wax or similar.