I am a machinist and was wondering if there would be any issues with machining a 3/8"(or whatever fits the frame) aluminum disc to modify an internal or integrated headset frame to a standard headset. Basically I would make a disc to press fit into the frame with a hole that would allow press fit of a regular headset. I've heard this mentioned but never heard of anyone trying it. Any thoughts or obvious problems I am missing?
You can easily do it (provided you have the right equipment), but they already exist.
Trouble is, I can't find any references online.
Back in 2000, Giant used these extensively on their XTC and NRS bikes. That year, they made those bikes with Zero Stack head tubes, but couldn't fill their order of Zero Stack headsets. So they pressed reducers into everything and sold the bikes with conventional 1-1/8" threadless headsets.
But watch out, one of their regional sales reps at the time told me they had a bunch of complaints of squeeking headsets and loosening problems. I figure it couldn't have been much different than, say, running a 1" reducer in a 1-1/8" headtube (which I've personally had some experience with and never gave me any trouble), or the plethora of OnePointFive to Zero Stack adapters that seem to be floating around out there.
Anyhow, walk into your local Giant dealer and ask if they have any of the old reducers laying about. I'll bet you can score a pair for pretty cheap.