Once the frame is in the correct position, he connects it to the preceding tread frame by welding it to a vertical riser bar.
When the stonework is done and the grounds removed, the treads will slip into the recesses with no need for scribing. The tops of the treads are screwed to the frame from below.
The author begins the new set of stairs by building a temporary platform over the basement stair opening and transferring key locations onto a hardboard template. Here he uses a laser to plumb down the location of the balcony header.
After drawing a full-size layout of the stair on the template, he makes patterns of the steel tread assemblies (above) and sends them to the fabricator.
The curved bottom plate is located by plumbing down from a laser attached to a trammel that pivots off the center point.
A carpenter shifts the position of the top plate so it’s in line with the beam that projects up from the laser.
The author uses a temporary wooden stage to support tread frames while he positions them over the template. The block taped to the corner of this tread has the same cross section as a riser bar; its center is being used as the laser target.