Sorry, just getting around to the forum. Been a horrible day. Couldn't even drag myself into work due to the back.
Anyway, I can due step boring where it is fairly smooth on the inside and no lip inside where the SS stops. The just means making the upper section a slightly smaller diameter. Non stepped the wood dia is 6.75mm and the SS is 4.75mm. I should have some larger bore cores coming. I do offer a hand made SS core made of 3/8" SS tube. I make it solid core and bevels flush with the wood at the top lip. But it is a monster drip tip almost as big as a nuppin. I hate making them as it takes me a ridiculously long time and I have to charge what I think is a rediculous price. Mainly all I charge for is my time, and hand turning, sanding, CA finishing 3 coats just already take a while. Adding almost an hour to make the core perfect....ouch. I would much rather not. Hoping all the option I can do with the premade cores will satisfy everyone's wants.
Also, one comment about the wood Rossum sent me. It did have some faint lighter sections and some character from growth lines. But the very first part of my process is taking wood blocks and cutting out round blanks. Very hot process and causes the sap (and even the dry looking pieces have sap when heated) to run to the surface. Usually scrubbing really hard with denatured alcohol brings back the figuring in wood, but for some reason the sap in the black wood was crazy hard and I barely got any figuring back. Ever tried acetone. After applying CA, think maybe too much, it just looks black. Should have tossed that one in the trash, but he has more coming in which I am going to try a different process. Unfortunately this is still a learning experiment for me, so it is what it is. I am honest about it.