In the original design phase for the Heirloom, I had considered what kind of feet might make sense with the curved bottom panel design. I looked at many of the standard designs in use on current laptops. I investigated how the laptop feet of my MacBook Pro are constructed. But nothing was really appropriate.
When I looked to resolve the issue recently, it became apparent that the metal side plates were the logical place to mount the laptop feet. But the available surfaces are quite small. I pondered the dilemma for a few days while attending to other issues.
I ordered a batch of 3/16″ balls in various materials to investigate the prospects. The Viton balls of about 70A durometer seemed to be appropriate. I then worked out a depth and diameter of hole that would hold the ball securely in place while providing just enough projection to properly engage with the desktop surface. I milled each hole with a smaller hole drilled beyond the cavity for a set screw just in case I decided an adjustment mechanism was called for. The feet are easily user replaceable and visually unobtrusive in a way that seems to work well with the overall design of the Heirloom.