Ferrite cores are available in about the correct gapping, but often with long leadtimes. I am looking for a solution that can speed development up
But good point about it being messy, no need to invent something that will mess up the CNC ?
-- Klaus Kragelund
How many pieces?
If only a few, wet lapping against a machined soft cast iron lap will do it.
If many, the spacer approach may be more practical.
Joe Gwinn
Let those who know how mess their's up.
RL
Depending on the shape and gap reqired, you might investigate available 'I' parts available for the smaller core types. These can be had as thin as 1.6mm - to use as outer leg shims - keeping the gap inside the build.
The mess of a cheaper glass grinder is probably justified for prototyping. Just don't plan to do anything in volume, with precision.
RL
Classically, diamond grit (or maybe SiC) in a slurry, applied with a copper wheel, is how a jeweler might do this. From time to time, you'd want to true up the copper wheel or disk.
If it's a prototype situation, could you utilize a highly-gapped E core, with several sizes of ferrite 'shims' (just diamond-sawn from sticks) that can be combined to form a variety of gaps? Diamond saws are simple and accurate, but a disk that can hit the center of an E core and spare the sidelobes, is gonna take some work. With a suitable diamond saw, producing thin slabs is easy (twelve inch silicon wafers being a standard item).
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