There are many different ways of turning a sphere. I will cover 6 different ways and also have a bit extra on the texturing that I did to these ones.
1. Matching a template
2. Mathematical turning
3. Ring check
4. Between cups (Most common but my lest favourite)
5. Shaddow guide (Least accurate)
6. Circles on laminated pieces (Limited)
7. By eye
8. Sphere cutter (I dont own one but its another option)
Sports balls. I wanted to turn some spheres and this way it as a bit more interesting. They are all made to scale.
Cricket (red cedar), badminton (American oak), billiards (Tasmanian blackwood/ huon pine), softball (Norfolk Island pine), table tennis (mahogany), golf (huon pine), squash (black walnut), field hockey (black hearted sassafras) and tennis (stained jacaranda).
Step 1: Matching a Template
I really like this method as it is really easy but you are limited by your template.
To get your template use 3mm mdf and cut out a circle using a forstner bit, hole saw or even turn one for bigger pieces. I used a forstner bit for this one as its neater than a hole saw. Cut the template through the middle to get a semi circle or smaller is also ok. (Pic 1)
Rough the timber down from square to round to the same diameter as the template. (41mm for me). Use a parting tool to square off the end. Mark lines from the end at 41mm and 20.5mm. The 20.5mm is the center line and the 41mm is the end.
Start on the exposed end and knock of the corner with any tool you like. Then start making cuts to roll over the end, making sure you keep the center line. I used a planing cut with the skew but using a thumb nail grind spindle gouge is also good.
Hold the template up to the work. Pic 7 shows a template too big and pic 8 shows the right size template. The gaps on pick 8 are fine for now. Where there is contact is where you need to make more cuts. Take your time and try not to get it all right in the first cut. After getting the end right, you can start working your way around the rest of the sphere continuing to use the template
When you are happy with the shape sand. If you look at the last pic, the timber can be held by a really small amount of wood.
Step 2: Mathematical Turning
Start with the same steps as the other, marking the center line.
Cut a 45 degree angle using a spindle gouge (pic 2). Its length needs to be the same as the end length and half the distance to the center line (pics 3,4,5). This is where the shape of the octagon starts to form. Mark a center line on the new angle. This is another line that is a final size.
Now to get it to a hexadecagon shape (16 sides). Start taking the high point so that its size is 2 times bigger than the distance to the center lines that are already marked. Mark another center line on that. (pic 7 and 8)
You can keep repeating this process to get it perfect but from here I felt I had enough reference points that I just blended it by hand, keeping all the lines. (pic 9)
Repeat on the other side. I used the tennon as reference for sizes at the end.
Step 3: Ring Check
Start with the same steps as the other, marking the center line.
What you will need is a metal circle. I found this plumbing piece, but you can use any metal pipe that is round. Sand the bottom flat so there are no bevels. It has to be a smaller diameter than the sphere but not too small.
Shape it by eye as best as possible. Hold a pencil to the piece while spinning and shade it in.
While the lathe is running on a slower speed, hold the ring to the piece. Where it rubs of the pencil, these spots are high. The ring should sit without a rock on a perfect sphere. Use a gouge or a scraper to take down the high points. Shade it again and repeat until its round.
You do get a bit limited at the end where the ring can not get to the end but by then you can get the rest by eye
Step 4: Between Cups
Fix to lathe with the live and dead centers. Mark your center and lengths. Shape by eye to get it as close as possible. Turn some cups separately out of a softer timber. Using the pressure from the tail stock and the cups, the sphere can be held without marking it. You can then turn it again, taking away high points, until you are cutting on all parts (no ghosting). You can turning it on as many axis needed to get it right. Same as sanding.
This is the most common method but I dont like it. When using another method you can cut the end grain easily where with this you turn into the end grain and against the grain on most axis. I find the cut on the timber is no where near as good.
Step 5: Shaddow Guide
Start with the same steps as the other, marking the center line. Start shaping by eye
Have a print out of many circles of different sizes. Use a lamp above the lathe to create a shadow. I used a magnet to hold the paper in place. The shadow should fill the circle perfectly of have an even gap all the way around. Not the most accurate but a simple method to get it close. You can change the height of the light to affect the size of the shadow.
Step 6: Circles on Laminated Pieces
Start with the same steps as the other, marking the center line. Shape it by eye.
The segmented section should be a perfect circle. You can use a template to check for gaps same as the 1st method. It is limited by only being able to check the accuracy of the circle area.
Step 7: Texturing, Carving and Inlays
So instead of just doing a few spheres, I had a sporting theme, making different smaller balls to scale. I covered squash, golf, billiards, tennis, hockey and softball
For the golf, hockey and the 2 dots on the squash ball, I used my foredom micro motor (rotary tool) to carve the dimples. Fairly easy just repetitive. With the squash ball, I filled the holes with yellow paint and sanded the top back after dry.
Tennis and softball, the challenge was in the marking out. I marked the quarter marks with a pencil and traced a cup of the right size to get the even circle. It took a few positionings to get it right. I used a brattle to make the correct line and then sanded back for the tennis. Then using diluted food dye to colour the jacaranda. I chose a good timber for staining and did samples to get the colour right. I then used the foredom micro motor to carve the rubber shape into the ball. For the softball I just used a wood burner.
The 8 ball was the harder one. Through many glue ups I got the inlay. To start I laminated 2 pieces together. I shaped half of it to get an idea of my boundaries. Using a forstner bit I drilled the 1st hole, took the piece off the lathe and made a plug for it. After gluing that in, I turned the plug down and repeated the process for the top half of the 8 with a smaller bit. It was a bit tight so it split the huon a bit. Then with different sized bits I did the other holes. One was off center so I plugged it with a dowel and re drilled it with a bigger bit. I turned plugs for them and glued them in, with the grain matching the direction of the rest of it.