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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.
ffm-
bearings exert an outward radial force on the cups
I understand that point and I am still thinking about it. But, if deformation exerted by the bearings on the cups would be a problem, then even with normal cups in a standard 1" setup for example, the bracing support by the headtube would never be sufficient to prevent a gradual deformation of the cup by the bearings over time, because the headtube is sitting quite a few mm below, not in the same "plane" as the cup itself).
But, apparently reality shows that this is not happening?One more thing to consider: the bearings itself in my concept are IS41 industry bearings, which usually have a closed stainless steel body. Unlike an open BB ring like it is used in 1" headsets, these bearings offer a certain structural integrity in themselves, helping to distribute any forces coming from the steerer much more evenly onto the cup
jetski
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.