The top, or yoke, of the fan-back Windsor chair that I am STILL working on is made from 1/8" thick ash, which is steam bent and has twelve 1/16" diameter holes drilled in the lower edge to receive the tops of the back spindles.
After bending them I realized that it would be easier to drill the holes before I bent them. After flattening them and drilling the holes I began to re-bend them, only to find that the ash crimped at each hole because the wood there was only 1/32" thick. Curious. They are in the process of being totally remade.
The back of the chair, in relation to the seat, leans back 5 degrees from the vertical, so I carefully set the table on my drill press to 18 degrees off the vertical and drilled all 12 holes in each of 36 seats. You are probably wondering why 18 and not 5 degrees. I wish that I had a rational explanation but can only put it down to a senior moment. I'm in the process of remaking the seats while the otherwise completed seats were used for kindling for my wood stove.