barefoot wrote:Well, the designer is going to have to accept the blame for whatever he got wrong, because he just clicked the trigger button for one of these:

(clicky through for big)
There was always going to be something
I really should have paid a bit more attention to those clearance dimensions around the crankset area. True to the standard disclaimer with XACD... you get what's on the drawing, whether or not that's what you really wanted.
I test fitted my 6750 Ultegra crankset yesterday. The inner ring hits the chainstay. I had a hunch it would, which is why I put them on. There's only a couple of mm in it, but we currently have an interference fit
If the stays weren't bent so much, to get around a hypothetical tyre that I have no intention of actually running, things would be just fine. The cranks themselves have plenty of clearance, it's just the 32T ring.
As a short-term solution, I think I'll build it up with an old square-taper RSX compact crankset I have in the heap, with a long spindle BB to push the chainline out a bit. That will work fine... but old solid-arm cranks and cartridge BBs are heavy bastards of things, and I've somehow turned into a bit of a weight weenie on this build.
For a long term solution... well, the short-term solution is to buy me some thinking time to work out what the long-term solution might be.
It used to be fairly common practice to push a dent in to the chainstay of a steel frame to get better crank or chainring clearance. I'm reluctant to do this, for fairly obvious reasons... and also because the problem area is just where the bridge is welded in, so deforming the shape of the tube there is going to stress the weld. Other options... maybe a triple crank, as is shown on the drawing, which would have a slightly wider chainline? Maybe figuring out some bodge with a Hollowtech 2 MTB BB, which (as far as I can tell) have narrower bearings and spacers, which can be left out to allow for a BB-mounted chain guide or front derailer or a wider BB shell. Maybe it would be possible to swap the spacers around to push the drive-side crank out a fraction (which would make the pedals assymetric... hmmm...).
Or any other suggested solutions from the assembled wisdom we have here.
Buggerbuggerbugger. Oh well.
tim