I made two more step stools as Xmass gifts this year. I start with 2 x 8 yellow pine boards which I plane down to 1 1/8 inch thickness. I then cut the various pieces to length. Two boards the width of the treads are planed down to 3/4 inch for the below tread apron and rear cross supports.
The next task is to edge glue the long and short side sections together. After the glue dries, the semi-circles are cut in the bottom of the sides on the bandsaw and then sanded with a pneumatic drum sander.
Now the dovetails can be laid out and cut on the side pieces. This way if the angles on the dovetails are a bit off, it will not matter, since the actual angles from the sides will be transferred (traced) on the treads. I used a bevel gauge to do my 15 degree dovetail layout. Make the pins a little taller than the tread width, so they can sanded down perfectly flush. I made the pins big because pine is being used. A hardwood stool could use smaller pins. I make the initial angled cuts with the table angled on my scrollsaw. I then cleanout the area between the pins on the bandsaw (just to the narrow side of the dovetail). Be sure to clearly mark the waste areas so you don't goof :). I finish the angled process with a pull saw or coping saw - depending on their location.
After the pins are cut in the sides, I layout the crosspiece dovetails under the treads and on the back. I use the same dovetail angle.
Now the cross brace dovetails can be cut. I use a pull saw and clean up with a sharp chisel.
The treads are now positioned on top of the sides. I clamp them together so they don't move while the tread is scored with the outline of the already cut pins. I can then cut the tails on the bandsaw, being careful to just stay inside the scored lines. The closer you stay to the lines, the less chisel fitting work there is to do later. The same process is repeated for the cross braces after the treads have been glued and assembled. Made sure to dry fit before gluing.
Here are two finished step stools. I finished them with two coats of Watco 'Fruitwood' Danish oil finish.