Originally Posted by
guy153
Car people (working with thicker walled tube of course) tend to actually bevel back the cut edge a bit if they use a hole-saw. Not so there's a gap but at least somewhere for the weld to go. Some YouTubers I have seen making bike frames notch with a hole-saw and then don't knock it back at all. This means the tubes fit perfectly, but there's actually very thin metal at the joint.
I think it's widely agreed that you should knock back those thin feather edges for welding. Bikes too, not just "car people". No need to knock them back for brazing, doesn't matter much one way or the other because those thin edges don't hurt anything, but they don't add any strength to speak of either. I leave them on, since grinding them back (beyond just de-burring) would be an extra, unnecessary step. You can also start with the tube just a fraction too short, which results in a miter that looks similar to one that's had its feather edges ground back.
I'll never miter with an angle-grinder since I have at least 4 other ways to miter that are faster for me, and I think probably just a little more precise. Pretty sure I can have my miters done before you've even got your paper templates printed and taped on. But I have big expensive tools. 3 of my 4 ways (mill, lathe and belt-grinder set up for mitering) involve kilodollar expenditures and a certain amount of shop space that they take up, so they're not for everyone. Nice to have though, for things other than mitering.
My fourth way is filing, which I'm fast at because I made frames full-time that way for 2 or 3 years before we got a mill. No paper templates needed when you just "know" how the miter is supposed to look. Oh and you need the right sizes of half-round, that cut the correct radius "automatically".
I've told this story here a few times but here it is again: When we got a mill, I raced with Glenn Erickson, and he filed his faster than I got mine done on the mill. Maybe Glenn was a little faster than me at filing miters but I was close. I don't remember how many filed miters it took before I was good at it, that was 45 years ago. I don't think it was all that many though; I think the first time I did it (with expert supervision) was more than good enough, though of course slower than I got later with practice. I can't swear, from memory, that the accuracy was perfect, but I think they were pretty darn close since I was mostly making lugless tandems in those years, more demanding of miter accuracy than say lugged joints. We only got the mill because our tandems had one continuous way-oversized top tube that was pierced in the middle for the cap'n seat tube, which was smaller than the TT. That pierced hole was tricky and slow with a drill, die-grinder and files, piece of cake with the mill.
It's because of that experience filing miters that I think paper templates are a waste of time. Maybe useful for a first-timer, but after that they're slowing you down. With proper filing technique, the paper does nothing.