The same lathe fixture and double-sided duct tape trick I used for the amber running light’s end cap should have worked for this one, but only after I re-learned the lesson about taking sissy cuts:

Yet another snippet of tape and sissy cuts produced a better result:

Protip: when you affix an aluminum disk bandsawed from a scrap of nonstick griddle to a lathe fixture, the adhesive will grip the disk in only one orientation.
Comments
One response to “Rear Running Light: Too-aggressive Turning”
[…] it onto a disk turning fixture and sissy-cut the OD down a little smaller than the eventual tube […]