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In the traditional way the headset cup is supported on both sides, internally by the steerer tube and externally by the head tube.
That's not right, in the traditional way the press-fit section of the cup is supported externally by the head tube (yes), but internally the steerer does not support it, it supports (if you can even call it that) only the cup itself which sits further up. With the press-fit section outside, forces are justed turned inside-out but the support is about the same. And the wall thicknesses (see my updated drawing) are higher too when it's external.
Of course it's always ideal if you use a 1" fork in a 1" steerer etc., but I am proposing a solution for a specific case that sometimes comes up here and there and I hope that people can take advantage from that, and the effort needed is actually quite low as it's really only about making the parts on the lathe. I will try the external cup now, thanks anyway for the input.
jetski-
I will try the external cup now
Yes! Excited for this despite not at all being interested in bikes old enough to not have a tapered steerer.
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If I understand it correctly the problem is that the bearings exert an outward radial force on the cups (and a corresponding inward force on the steerer) in addition to the axial force. In a normal headset the cups are braced against that radial force by the headtube, but in your design they're not. Instead you're relying on the strength of the cup itself to resist any non-axial forces that might deform it. If the cup does deform then it might unseat slightly from the headtube and, even if it can't walk off it, it might fret and wear both itself and the headtube.
I assume that's why previous efforts at this have actually brazed or bonded the cups to the headtube.
Tijmen
ffm
But you're not applying the force in the same way.
In the traditional way the headset cup is supported on both sides, internally by the steerer tube and externally by the head tube. You have no support outboard of your cup because it goes over the head tube. I'm not an engineer but I can tell you your way is going to be significantly less effective.