Turned and Decorated Sphere archive

Wednesday 30 September 2009

Tracy Owen turns and decorates a maple spherical hollow form

Gallery

Experimenting with turning a sphere has been a good learning curve for me; achieving a perfect sphere in itself is quite a challenge. In this article I will show you how to use a cup chuck, which will help to deliver good results. Ideally the cup chuck should be made from soft wood so that it does not mark the sphere you are turning. I chose to hollow out and decorate my sphere, but you do not necessarily have to do this. It could be left solid, providing that the wood is dry enough. A solid block of wood this size that was not bone dry would almost certainly split. I chose to make this sphere 125mm (5in) in diameter, simply because I had previously been making some this size and I had made the jig to do the necessary holding. However, these spheres could be made to any size. If you wish, you could use different timbers bonded together to add contrast. Also, have a think about what a sphere shape could be used for, such as a table lamp, night-light or a clock, to name just a few possibilities.

1. The completed sphere

2. Take a maple blank measuring 140 x 200mm (5 1/2 x 8in). The piece I used had a moisture content of around 20%

3. Mount the log between centres and turn to a cylinder using a 10mm (3/8in) bowl gouge. Lathe speed is around 700rpm

4. Next, shape the sphere using a 10mm (3/8in) long-ground bowl gouge, working from the centre outwards, cutting downhill. This will give the cleanest cuts. Draw a pencil line on the centre to help you to judge cutting equal amounts on each side. Increase lathe speed to 800rpm

5. Here you can see the previously mentioned cuts, only this time on the left hand side

6. Use divider callipers to get the diameter close to what is needed in the centre. I set mine at 125mm (5in) as I already had a cup chuck this size

7. You will now have a shape close to what is required. Cut each end down to about 6mm (¼in). These will then be cut through with a saw so that the piece is ready to be mounted into the cup chuck

8. You will now need to make a cup chuck, preferably from a soft wood - I made mine from ash. Your cup chuck will require a dovetail on the back and will need to sit into the jaws of the chuck

9. You now need to turn the sphere 90% round and tap into the cup chuck with a rubber mallet. If your sphere is still out of the round it will still require turning away using a 10mm (3/8in) bowl gouge, once again working from the centre cutting downhill. Lathe speed is 700rpm

10. A small tap on the back of the cup chuck will release the sphere. You will then have to move the sphere into a slightly different position and tap it back into place

11. You may choose to use a shearing cut rather than bevel contact, as this will allow you to take smaller amounts with each pass - these cuts are really used for the final shaping. For this, use the 10mm (3/8in) bowl gouge which has the same grind as the previous one – this will save you grinding. These will be the last cuts before sanding. Increase lathe speed to 1000rpm. You can of course use a scraper to refine the shape if you choose

12. When you are happy that the piece is nice and round it is on to the sanding. You should now have a good fit in the cup chuck. Sand half the ball and then move around until the whole surface has been finished. You can sand this by hand or you can power sand using 120, 180, 240, 320 and 400 grits

13. Next, make a jig to hold the sphere. I made mine to hold a 125mm (5in) sphere but you can make yours to suit whatever size you want. The jig consists of a disc mounted onto the jaws of the chuck with a dome-shaped cut out to suit the size of the sphere required. An MDF ring holds the sphere in place with four short lengths of stud iron and wing nuts for quick adjustment

14. Draw on the pencil lines for the start of the decoration which is going to be a series of five small ‘V’ cuts, or grooves cut into the six different faces. The shaded one in the middle should measure 15mm (?in) in diameter and will be the aperture to hollow through later. To achieve these measurements, measure 45mm (1 3/4in) out from each centre, scribe a pencil line and then, with the lathe running at 800rpm, divide the two lines by eye with a further four pencil lines

15. To cut the small ‘V’ grooves use a skew chisel on its side, as this gives really good control. Ensure that the tool is freshly sharpened to achieve good results. Lathe speed is about 800rpm

16. Sand each set of grooves with a piece of 400 grit folded to produce a crisp edge. Move the sphere 90° and the previously cut line will then be in a horizontal position in the jig. The sphere will then be in the next position to cut the next set of rings. Repeat this until all six sets of rings are cut out. Be careful and accurate during this process. Precise marking is necessary - if this is not the case, the eye is likely to spot any deviations from the pattern chosen. It is important to be as accurate as possible – all the decoration needs to match, right round the circumference of the sphere

17. Having put on the six sets of decorated circles, add a further eight smaller sets of two circles in the spaces left between the bigger sets. To get these in the right place, move the sphere in the jig to roughly the right location and then use the tip of a pencil slowly rotating the sphere and jig by hand, eyeballing the largest of the previously cut lines passing the end of the pencil. Once each of these three lines tallies up with the pencil, the sphere is in the right place and will then lock into place in the jig

18. Draw on the pencil lines ready to make the ‘V’ cuts

19. Use the tip of the skew chisel to make the ‘V’ cuts and repeat eight times. Lathe speed is about 1000rpm

20. Start applying the first coat of oil to the sphere. Ensure that the sphere does not roll off your bench whilst you are working on it. Rub the oil in well and remove the surplus, then buff to a finish

21. If you prefer, you can leave the sphere like this in its solid state, or you can choose to hollow it out and decorate it

22. For the next stage you will need to drill a hole to the depth of 115mm (4 1/2in) with a 13mm drill. Mount the drill into the tailstock with lathe speed at about 300rpm

23. Use a 10mm (3/8in) spindle gouge to open up the neck from 12mm (1/2in) to 22mm (?in). Lathe speed is increased to 600rpm

24. The first part of the hollowing is done using a 10mm (3/8in) spindle gouge. This should be carried out with the tool over on its side, cutting on the bottom wing

25. I discovered that the aperture does not need to be 15mm (5/8in). My thoughts were that if I cut too large an aperture it would interrupt the shape of the sphere. The first thing you need is a small hollowing tool - I chose to use a set of three McNaughton hollowing tools - their bar size is 8mm (5/16in) in diameter and they have three different offsets – I only needed to use two of them. These were the two with the least offset. Even with a small sized hollowing tool it was still a challenge to get through a 15mm (5/8in) hole

26. I decided to also add some pyrography for further decoration. Again, this is personal choice, but you can also choose to use this technique if you wish


Woodworkers Institute

Tagged In:

hollow form , Tracy Owen , Pyrography , spherical , cup chuck

Glossary Rollover a term to view its definition

Tailstock , Tang , Lathe Steady , End Grain , Bowl turning attachment , Centrifugal Force , Coated Tools , End Grain Turning , Fishtail Tool , Skew Tool

Tools Used

Set of three Kel McNaughton hollowing tools (or any other swan-necked hollowing tool), 10mm (3/8in) spindle gouge, skew chisel and 10mm (3/8in) bowl gouge

Top Tips

A small aperture makes it difficult to get the shavings out and the neck is more likely to get broken because of lack of space around the hollowing tool. To help prevent tool movement use a ‘U’ shaped holder to locate the hollowing tool, making the job a lot easier

Diagrams Click an image to enlarge