[rallyhub]

So I looked around the workbench and came up with some 3/32” square brass tubing that even I could cut and file to fit. Secured in place with some IC2000 adhesive it works great. The chatter is significantly decreased.

Maybe next time you can think of a vertical strip instead of square. It gives even more rigidity.
For example: Instead of square 3/32" you can take a 1/32"x1/4" brass strip, which is about 10% lighter and its moment of inertia is more than six times greater;
which means six times stiffer.
Ix=1/12bh³
Square 3/32" Ix=2.673mm4
Strip 1/32"x1/4" Ix=16.93mm4

Hub