Now that the stair tread was cut, we needed to create a curved riser to fit. Since we plan to paint the riser, we had a few options for its construction, but I decided to make it out of a piece of oak so as to match what would have been done when the house was built in the 1920's. We could have used snake ply and covered that with a veneer, but this seemed lazy to me and would not have been much cheaper or easier than using oak (and I don't know if veneers are available in a 10' length?).
The first step was to cut boards to create a form that the oak riser would wrap around. This was accomplished by tracing the curve of the stair tread onto pieces of 1" board and cutting them out with a jigsaw.
The boards were then lathered with construction adhesive, clamped together (six boards in total for a 6" form), and left to dry overnight.
The forms were then sanded with 60 grit sandpaper to make a consistent, round form.
The forms were then secured to the stair tread using construction adhesive, wood glue, and corner braces. We were actually able to use the form from the original stairs on the smaller curve; two forms that we created were used on the bigger curve, and then a piece of plywood was used for the straight portion.
Now for the fun part. The riser was created out of a 10' piece of 1" oak. I was sure to pick out a piece of wood that was quartersawn (grain perpendicular to face of board) so as to limit the risk of the board splitting when curved. I measured the length of the curved areas and marked those on the board. I then cut hundreds of little kerfs across the back of those curved areas, spacing them 1/4" apart and leaving 1/8" of board on the uncut side (I probably could have gone with 3/8" spacing since our curves have a large radius, but I wanted to be conservative). I had originally planned to do this with the table saw, but it was just too difficult and slow to cut across a 10' board, so I used the circular saw instead and that worked fine.
We then secured this board to the forms using a ton of wood glue, as well as some 3/4" screws on the straight portions. This was clamped and left to dry for 24 hours, and then the overhanging board was cut off.
