Today I will describe how I re-created the missing 1st and 6th frets.
First, the scale length had to be determined. I did this using Stewmac's online fret program. Using existing frets 2 through 5 and the nut as references, I calculated a scale length of 71.9 cm.
This number falls within the range of Pipa scale lengths I've seen. Fortunately for me, this instrument uses a twelve-tone scale!
I hotglued squared mahogany blocs and the nut into place. The nut's in sad shape but will suffice for measurement purposes. From the fret spacing table, I marked the locations on blocks #1 and #6 where I want to inlay the bone.
After squaring the cuts, I used the fret saw to cut the channels to a depth of approximately 3/16"
The rest was finesse. Using the sanding drum, Dremel tool, and coarse papers, I coerced the bone pieces and fret channels to fit together snugly. I cut a slight radius (you can't see it) on the underside of the bones before the final superglueing. This helped to give the side-view appearance a nice clean look, with no visible gaps bewteen wood and bone.
Finally, the angles were cut. They will be feathered-down to the precise height needed to form a perfectly straight line along the apices of all six blocks. Here's he roughed-in #1 block.