Originally Posted by dookie
what? 0.4mm of wall thickness seems like an awful lot to be removing. eg: reynolds 853 *is* 0.4mm thick (presumably not at the butts)! how much thicker is aluminum?
it's one thing to flex-hone the tube, but you'd need a machine shop to take out 0.4mm and a cut that drastic would have to compromise the strength of the tube.
this sounds like really bad advice to me.
Sorry, I missed this post earlier...
Let's assume the OP is converting a frame w/ a 28.6mm ST. Let's, for the sake of argument, assume that it's made out of SL (which it probably isn't - it's probably made out of something cheaper, thicker and heavier). I've seen and touched SL STs with a bunch of different internal diameters - 26.8, 27.0. 27.2, etc. So, if the outside diameter of these various STs remains constant at 28.6, but the internal diameter varies, that would mean that there's a difference in wall thicknesses even within one tubing type. If one SL ST is safe at 27.2, why wouldn't another be safe at 27.2? Either way, it's still .8mm of material at the top end.
When you're building a steel bike, you ream out the seat tube as one of the finishing steps to account for distortion from the heat, etc. Scary it may seem, it's not rocket science and is no more likely to make your bike explode into a pile of firey slag than drilling out your track fork. It's just part of the process of building the bike.
As far as 853 goes, show me a frame made of 853 that takes a 26.0 seat post. Ain't gonna happen.