Here is the cutting angle chart with fractions.

Scroll saw bowl instruction 

Turning Ring Bowls

Ring bowls can be made from one flat piece of board or a number of pieces glued together.

The thickness can vary although 3/4 to 1 inch IS common thickness. The thickness will also have

a bearing onthe height .of the bowl and the thicker the board, the more difficult to cut on the
scroll saw.  The board can be most any size that your 'lathe capable of handling. The swing on

my lathe happens to be 12 inches so my target is 11 1/2" material.<                       .          .      .        

After selecting your board you should plane or sand the surface of the board to obtain level
surfaces on each side. Next, using a caliper measure the thickness of the material on at least 4
sides and using these measurements determine your average thickness. For instance, (use
sample board with rings).  

Layout: Using a compass, draw the largest circle possible on your board. Measure 3/4" inside
that circle and draw another circle. This will become the top ring on your bowl. Continue to
draw 4 circles each 5/8" apart. If you are talented with a scroll saw, that measurement can be
reduced to 1/2" and could get an additional ring from the material.

Thickness: Now using the average thickness of your material go to the chart to determine the
angle to cut your rings. To prep for sawing a small hole needs to be drilled at the same angle as
the saw cut.

Please note that the inside ring is cut first, working your way to the outside of the material.
Important: The outside ring should be cut on a band saw not using the degree angle.

Sanding; It is helpful to have a flat sand area to smooth out your rings before gluing The best
system I have seen is using a 12" floor tile and placing a 12" sanding disk on it. Using a circular
motion you get a near level finish and avoid gaps in your rings. Otherwise light sanding on a flat
bench top will do.

Gluing; After sanding your rings they need to be carefully matched up and glued -. If you have
used a different kind of wood in your material this will serve as your benchmark. Otherwise
making a pencil mark on the board before cutting your rings is helpful. Sometimes the grain in
your wood will suffice. If you want the bowl water resistant bowl, I would suggest using
Titebond II glue. Aligning up the rings for gluing is very important. Pencil marks before
applying the glue can serve. as guides. Suggest using a bowl clamp for glueing or you can use
your drill press. Allow to dry overnight before putting under stress.

Preparing, For turning bowl:

Attach waste block to bottom of bowl. Place a sheet of craft paper between bowl and waste

block. Can be easily separated from bowl. Use lathe to glue and center block on bottom of
bowl. Also allow to dry over night.

For safety use tail stock to hold bowl while turning outer rings. Always turn outer rings on
inside and out first. You can remove tail stock so you can finish inside bottom of bowl.

If your tailstock is not long enough to reach bottom of bowl suggest using a small block of wood

this will prevent damage bottom inside of bowl.

Finishing outside bottom of bowl:

Once you have completed the turning, sanding and applying the finish you intend to use, you can
then remove the bowl from the lathe, The waste block can easily be removed by carefully using
a wood chisel to separate the bowl from the block Reverse the bowl and place it on a.bowl ,
chuck large enoughtohold your bowlsecurely. You then finish the bottom in the fashion you
desire. A concave bottom will prevent rocking when placed on a flat surface.