I recently bought a small box of these 37° champer cutters, though there were no arbors to mount them in.
Today I needed to form a champer for a -6 SAE oring boss fitting.
Here is what I made the arbor out of
U took a 1/2" socket head bolt then turned the head then drilled and tapped to accept the cutter then cut the threads off the bolt.
These bolts are hardened and usually grade 9 just about as close to being tool steel as you can get