Pretty cool design.I'd say that's probably the worst possible place to lose weight though. The part you machined away is were most forks bend assuming the legs hold. I've bent plenty over about 30 years, trust me.If anything, machine out the inside of the top of the headtube. You could probably get by with it pretty thin, you've just got side impacts from the bars hitting the ground with very little weight on them.If you absolutely have to do it at the bottom, do it on the inside so the larger outer diameter can help strengthen it.
Very nice! But 22'' tt is it for Trevor?
I am intreged by the 100 mm rear spacing and special BB that would indicate this was for a crank less bike.However the 9 x 9 drive has put a different perspective on this frame.