Bob,
D bit (we used to call them half reamers) reamers are slow but work well. I have made a couple with satisfaction; you have to watch the "relief" at the diameter changes. You also have to grind them in half (not the pilot) after hardening, to prevent warping.
Mike
I've made a few d-bit cutters out of solid carbide using a diamond wheel. No warping. LOL.
Yeah, I know. A piece of carbide big enough for a 16ga reamer would probably cost as much as a finished HSS reamer. Also my little TC grinder doesn't have the range to make a tool that big. I do have a surface grinder, but that's not as easy (for me) to make round cutting tools on. Okay, maybe mostly because I just haven't used it that way. I'm having visions of setups dancing in my head like its Christmas Eve.
Dang-it. Now I want to do it just to see if I can.
One thing I found is sometimes I just have to get in there and grind a relief by hand anyway. I made an 18 degree (144 degree included angle) chamfer tool the other day, and that was the only way I could remove the heel easily. Like back relieving the heel free handing drill bits on the bench grinder.
