Shrinking the tubes, as opposed to expanding the monobloc with heat, is a fascinating variation on the Cannons Frettes method. Would it make any practical difference regarding the tube being shrunk in and then expanding to contact the monobloc rather than the other way round?

Really impressive is the surface finish quality on the monobloc. Is this surface finished-polished after the machining or is it direct from the machining? It looks like it has been beadblasted but that might be the photo quality.

I would love to get that kind of result from machining alone!