Off-centre Winged Bowl archive

Tuesday 29 September 2009

Gallery

The idea for this project is something I have been working on for the last few months. This is about the sixth version I have made, each time changing the sizes or angles to hopefully improve its form. This is an interesting form to make, although it is somewhat challenging. When making the first half dozen I used my vacuum chuck system to do the re-chucking part and the alteration on the angle of the rim – this made it so easy. For this article, I have used a jam chuck instead, which also worked very well. Obviously, the wood and the jam chuck need to have the right fit so that it is held securely. I feel this form still has potential for further exploration by adding carving, texture and colour, etc. The choice is entirely up to you.

Step 1

Start by drilling two 7mm (9/32in) holes 10mm (3/8in) apart so that the blank can be mounted onto a screw chuck on two different centres. This burr oak blank measured 200 x 125mm (8 x 5in) and had been drying for some years. Its moisture content was about 24%. Using a screw chuck, mount the bowl on the centre hole. True up the outside using a 10mm (3/8in) bowl gouge, this will be the outer edge of the finished wing when the project is complete. Use the tailstock for additional support with lathe speed at around 700-800rpm

Step 2

Now mount the blank onto the second hole, which is 10mm (3/8in) off the centre, using the 10mm (3/8in) bowl gouge to do the shaping. If you look closely at the piece you will be able to see some ghosting as the piece is rotating; use the tailstock for extra support

Step 3

This is the shape you should have after the first few cuts. Cut the 63mm (2 1/2in) dovetail using a 10mm (3/8in) spindle gouge. This spindle gouge is ground specifically to do this job. Now shape the underside of the bowl using the 10mm (3/8in) bowl gouge; the long-ground profile of this tool will allow you to cut into the tight corner under the wing. Lathe speed is still around 800rpm

Step 4

You now need to cut the underside of the wing: this is with bevel contact cutting at the very tip of the tool. Remember: the outer part of this wing is hitting and missing the tool because it is off-centre, therefore, good tool control is essential

Step 5

Here you can see how the long-ground gouge can cut into tight corners from either direction. The underside of this is finished for now, but because the bottom of the bowl is not going to have a foot it will require further shaping. This will be done once the top face has been completed by reverse-chucking and holding it in a jam fit chuck

>Step 6

You now need to turn the piece around and mount it on the earlier cut dovetail. Here you can also see the wonderful figuring in this piece of burr oak

Step 7

You now need to draw a pencil line onto the rotating wood: this pencil mark lines up with the outside edge of the bowl, below the wing. Your aim is to get the shape of the top edge of the bowl to match the shape below the wing

Step 8

It is now time to cut the top of the wing; these are very similar cuts to the one used on the underside, working from the outer edge to the middle with the 10mm (3/8in) bowl gouge. As the tool gets towards the end of the cut, roll it over on its side so that the bottom wing of the tool does not catch

Step 9

Now cut the outside of the top half of the bowl using a 10mm (3/8in) bowl gouge. The bowl needs to be shaped so that it forms a continuous flowing line with the bottom half below the wing. Lathe speed should be around 800rpm

Step 10

Now cut the inside of the bowl with the long-ground bowl gouge, this will then be swapped later for a short-ground bowl gouge. Lathe speed is still about 800rpm. When cutting the inside of the bowl your aim should be to keep the wall thickness equal all the way through, and also to keep it the same thickness the wing was cut to

Step 11

Use callipers to check the wall thickness; this is achieved with the lathe stationary

Step 12

Use a 12mm (1/2in) short-ground bowl gouge on the inside of the bottom half of the bowl. This shorter grind is needed to get a controlled bevel rub cut round the bottom

Step 13

Shear scrape the inside of the bowl with an 32mm (1 1/4in) round-nose scraper, used on its edge at about 45 degrees to the wood. When used this way rather than flat on the toolrest, it gives a cleaner cut. Reduce lathe speed to 600rpm. The outside top half of the bowl and the top side of the wing all require power sanding using 120, 180, 240, 320 and 400 grits with lathe speed at about 500rpm

Step 14

Here is the jam fit chuck with a dovetail on the bottom to fit into the jaws on the chuck. It can be used many times, not just for one project. Cut the aperture so that the top half of the bowl becomes a snug fit (it needs to be able to be tapped into place and removed without any damage). The tailstock will be used to centre the piece and left in place for extra security. It will be later removed to make the last few cuts on the piece

Step 15

Using a 10mm (3/8in) bowl gouge, cut away the dovetail that was used to hold the piece earlier. While the tailstock is aiding the jam fit chuck, sand the underside of the wing and the bottom half of the bowl. Power sand the underside of the bowl, except the last bit in the centre. I suggest doing it this way as the tailstock helps to stop the piece from getting dislodged from the jam fit chuck

Step 16

Make the last few cuts with the tailstock removed. The piece is held entirely by the friction in the jam fit chuck

Step 17

Hand sand the last couple of inches using 180, 240, 320 and 400 grits

Step 18

Here is the piece so far. If you wished it could be left like this and oiled, but I chose to fit the base back in the jam fit chuck at an angle, and changed the shape of the rim

Step 19

Now mount the piece into the jam fit chuck at an angle. Rotate it gently by hand and use a pencil to show where to cut. I chose the lower part of the rim on the shortest side of the wing

Step 20

For extra security use a revolving centre with interchangeable heads. Turn a piece of wood to fit one of these heads which will be used on the inside bottom of the bowl to help keep the piece in place

Step 21

Use a 10mm (3/8in) bowl gouge to trim back the rim to the previously drawn pencil line. These cuts need to be very thin because the inside of the bowl has been finished and you do not want the edge to break away. This rim will then require some sanding

Step 22

Now give the piece its first coat of oil. You could use Danish Oil, as I did, but there are many other types of oil that can be used. It will have at least two more coats, leaving sufficient drying time between each


Woodworkers Institute

Tagged In:

Bowl , Tracy Owen , vacuum chuck , burr oak , faceplate

Glossary Rollover a term to view its definition

Bowl Gouge , Faceplate , Bandsaw , Lathe , Toolrest , Off Centre Turning , Chuck , Burr , Vacuum Chuck , Danish Oil

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