In the last two days, I’ve made same progress. Yesterday, I ground some glass for the back:
Messy, but effective. I use a lapping glass and 500 grit silicon carbide lapidary grit. Light pressure, lots of rinsing and checking. I cut the glass to fit the back. No clipped corners on this one.
The springs are surface-mounted; this first pass, I left the turned ends proud of the surface. I thought I’d see how they worked, and if too tight, I’d create recesses for the ends later. I used 3/4″ x #17 wire brads as mounting pins; just set the frame in place and press the pins in to mark their locations.
Predrill the holes so as not to split the wood, cut off the heads of the brads, and tap them in place. And it worked well. Except the springs applied too much tension as installed. I needed to recess the ends. Easily done with a Dremel and straight bit.
An appropriate amount of force is applied to the holder, but there’s easily enough flex left in the springs for removal.
I have only a few more things left to do before applying finish: Cut the hole for the plate back’s locking tab, ease the back of the ground glass holder grip to make grabbing it a little easier, and maybe rout a recess under that end in the insert to facilitate even easier insertion and removal of the holder, pending a bit more testing. Finish sand, ease the edges, and apply tung oil finish. Wait a few days, lacquer, and it’s done.