
Completed Pivot Plate
There's nothing new about this. We didn't discover the Higgs Boson.
I was curious about the various pivoting azimuth plates being sold - this, for tonearms without an azimuth adjustment feature.
Also, tonearms with removable headshells with azimuth adjustment capability can be frustrating to work with. You'll find yourself overshooting and undershooting the mark by a considerable amount.
Forget about repeatability.
Our azimuth gauge will demonstrate how those "small" changes you made are in fact 4 or 5 degrees, and this will frustrate you further.
So, a pivoting azimuth plate has the potential to simplify your life - even with a tonearm having crude azimuth adjustment features by adding precision and repeatability.
The "Build"
My luthier's nut vice (don't laugh) has served me well for rapid prototyping of small parts like this.
With some tedious filing, I fabricated a working prototype, by pressing one of our aluminum headshell shims into service as shown above.

In Action (click to enlarge)
The process involved filing a flat section on a set screw, and then epoxying it to the headshell shim. For the brave of heart, a permanent installation would involve affixing it to the bottom of the headshell.
Learning Curve
Adjusting azimuth involves loosening one screw while tightening the other in order to tilt the cartridge.
Making fine adjustments can be tricky, in that you run the risk of moving the cartridge and undoing your careful work with your protractor. There's a simple trick to prevent this from happening.
Make the adjustment in multiple steps. For example, it you want to loosen/tighten by 1/4 turn, make 4 adjustments of 1/16 of a turn. Experiment with how small of an adjustment is required to not disturb the cartridge's position. There's a bit of feel involved.
Changes I'd Make
For this first try, I used a 6-32 set screw from my fastener collection. This is much too large of a diameter.
If you're planning on experimenting with this, I'd recommend sourcing a #4 set screw - something like this. I'd prefer a #3 screw, but I don't see any of sufficient length.