After a week of use, Mary decided the single additional graphite disk in each stack produced a too-high initial speed when the sewing machine started up; this being a matter of how it feels injects some of trial-and-error into the repair.
Shaving a graphite disk down from 0.8 to 0.4 mm seemed entirely too messy, so I snipped squares from 0.40 mm = 16 mil brass shim stock, nibbled the edges into a polygon, and filed the resulting vertexes to produce a (rough) circle:
Each stack looks like this:
- 1.5 mm graphite disk (double-thick)
- 0.30 mm brass (original part)
- 0.79 mm graphite disk
- 0.40 brass (new part)
- The rest of the stack
Protip: dump those shards onto a strip of wide masking tape, fold gently until it’s all corners, and drop in the trash. Otherwise, you’ll pull those things out of your shoes and fingers for months…
You can get cheaper nibbling tools nowadays; I’ve had mine for decades.