Is it possible to make air gap in pot-core which doesn't have it?

@MrAI

Working with ferrite cores reminded me mostly of the days when I did glassblowing. I suspect a small score would help direct the fracture, and maybe forcing a tapered rod into the hole with the score on the outer perimeter would help more. A little spit on the score also helps, at least with glass. I just used a thin abrasive cut-off wheel (not the fiber reinforced one) in my Dremal. I put a wet sponge next to it and cut through the sponge and ferrite at the same time. That gave adequate cooling.

As for high-temperature adhesives, there are of course purpose made ones available. For a cheap substitute, you might consider water glass (sodium metasilicate and other names).

John

al, i often use flyback cores for various medium size toroids. they are already in halves and can be reassembled with or without shims, and they often come with a spring that holds them together. crt yoke cores are useful for larger toroids, and are also made in halves. just as long as you don't mind the somewhat conical cross-section.