The process has to start with a drawn plan. I draw what I want the shape to look like and then draw in the blocks that represent the cross section of the wood rings. Always allow at least 3/8" on either side of the desired bowl wall. Anything less than that may mean that you will not have enough material to get the shape you want. It's easier to remove wood than to add it.
Even if you have deep pockets and can afford to buy the $2000 table saw, you'll still have trouble trying to cut consistently accurate pieces. My saw is a $99 portable contractors model and accuracy isn't one of it's strong points. Saws in this price range have the blade mounted directly to the motor shaft and you'll get a lot of side to side wobble when it starts up. Also, as the motor heats up from continuous use, the blade will move up to 1/16th". If you want to rip very thin strips, let the motor cool between passes.My solution is a cut-off sled. It's made from 3/4 MDF, wide enough to support an adjustable angle guide and deep enough to keep your fingers away from the blade. It runs in the mitre guage slots that are in the saw's tabletop. I made runners out of 3/8 aluminum channel.
In practice, I loosen the bolt holding the adjustable angle guide and place the protractor against the side of the saw blade and against the front of the adjustable guide. I move the guide to match the protractor angle until the angle is correct and then tighten the lock bolt back down on the adjustable angle guide. In the picture, it's the bolt with the washer on the right side of the sled. You are looking at the sled from the back of the saw. In use, you would be on the other side, behind the handle.
The clamp on the right side holds a stop block (precut to the angle you are using). This stop block is set to the width of the widest part of the segment. Material is fed up to the stop block and then clamped in place with the clamp on the other side. The whole sled is pushed into the blade path and the segment is cut. Each segment cut in this manner will be within .002 - .010" of each other.
Note the cotter pin extractor lying on the sled. Cut segments will often stay on the sled, so I use that tool to pick them away from the spinning saw blade.
Here the pieces for the feature ring have been cut. All 340 of them. They will be glued up, layer by layer, until a complete segment has been made.
Here, the first three layers have been glued up and are now ready to have any rough edges lightly sanded. When working with glue (Titebond II is the best) I tape wax paper to the work surface. This keeps the segments from sticking to the bench and also keeps the bench surface clean.
After gluing up 3 layers, there is bound to be variances in width. It's essential that mating surfaces be perfectly flat. I sand the faces using my homemade disk sander and then use a digital caliper to measure and note the thickness of each one. In this case, I have arranged the segments by size, with the thickest on the left and thinnest on the right. Then I pair them up, taking one from the thick end and matching it with it's thinner friend from the other end.
Because these segments are complicated, each is built as an individual. So it is necessary to cut them individually as well. I made this sled to slide along the saw's fence. Each segment had to have the one end cut carefully in an attempt to establish a consistent margin. Then they could all have the other side cut using the same fence set up.
After completing the feature ring glue-up (it's in the upper right of the picture) I start making the rest of rings. Segments for the various rings are cut to their respective widths, calculated by using a formula. The width is determined by dividing the circumference by the number of segments you want. The angle of the segment's sides is determined by dividing 360 by the number of segments and then dividing that number by 2.After cutting the segments, I use a sanding block with 220 grit sandpaper to lightly remove any burrs left by the saw blade. I use an 80 tooth blade, so the cuts are pretty smooth, but softer wood will still have burrs. Then I place them in position and put a ring clamp on them to check the fit. If there is a gap, I'll remove a couple of opposing pieces and sand the adjustment on my disk sander. I'll continue dry fitting with the ring clamp until they all fit together with no gaps.
Then I'll apply the glue to the segments and clamp them into their final postion.
After the rings have been glued up, I pass them through my homemade drum sander to make their surfaces nice and flat. Then they are stacked and glued up. When dry, they are glued to the bowl base and the whole assembly is then glued to a waste block that is mounted in the lathe chuck.
After turning the first few ring to their rough shape, I glue the feature ring into place. This is left to set overnight.
Another view of the inside. Normally, I would have glued up all the rings, but this bowl will have a top that is pretty closed and the depth of this bowl won't allow me to reach down to the bottom.
With the bottom half turned, the rest of the rings are glued up and turned.
Here's the completed bowl.
