DMAIC gets associated with continuous improvement on existing lines, but it's just as effective when you point it at a piece of bench hardware that nobody loves.
For the Jominy fixture, the Measure step was where the project actually turned. Once we had Cp/Cpk numbers, the conversation moved from 'this fixture is annoying' to 'this fixture is the special-cause variation'. That reframing made the redesign obvious.
The Control step is what makes the gains stick. Control charts on the new fixture are how I know the 80% COPQ reduction wasn't a fluke of the week we measured it.