Denny showed both open and closed segmented bowl turning. He feels that open segments are actually easier than closed ones. He starts with a program in which he designs the bow or vase. The program then produces a table showing all the segments and there size to the third decimal place. For both types, open and closed, each segment has to be cut at an exact angle. Denny has tried all kinds of miter gauges, but the most accurate are the sleds he builds himself. A dedicated sled for each angle. For a 12 segmented bowel that is 15 deg. 
For a closed segment bowl he clamps each segment in a hose clamp to hold it together while the glue dries. 
He likes to use Gorilla glue. To flatten the surface of the first layer he hot glues it to a plate on the lathe and turns it flat. Each successive layer is glued to the previous one using a home made cone to center it.
Each layer has to be flattened and thicknessed exactly.
Open segmented bowels are done quite differently. Each segment is glued on at he lathe using another one of his custom home made jig to locate it at the exact angle and distance from center.
Any glue that squeezes out has to be cleaned up immediately.
Then the layer is flattened and thicknessed just like with the closed segments.
If the neck of the vase is narrow he turns the inside of it as he adds layers.
We have all seen the beautiful results of Denny’s work, and now we have a idea of the patients and care that goes into making one