Originally Posted by
bulgie
There's a youtuber who goes by something like The Fabricator. I watched his video on notching tubes, which he does for making roll cages for race cars. He notched with a flap wheel in an angle grinder, quite crudely compared to what I'm used to, and said something like "There — perfect tube notch!" Looked worse than the worst miter I have ever done, but I have no doubt it's good enough for the thick stuff he makes rollbars from. Thin bike tube would warp all over as those big gaps pull closed.
I trust your standards are higher than his, I'm not lumping you in with him! Also I will grudgingly admit that my insistence on "water-tight" miters is overkill. I probably do let Perfect be the enemy of Good sometimes.
Yes and no
If it's a straightforward mitre it's very good, like you can't see any light there and it's really touching all the way around. But, especially on some of my earlier frames, I have had some bigger gaps with some of the trickier spots, like at the DT/ST/BB shell that has a double-mitre. Also the first jig I made wasn't great. But I welded it anyway (I'm quite good at welding across gaps due to my often not great fit-up
but have never had any significant distortion post-welding, although I was quite afraid of it.
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. Then they weld it with "pulse and lay wire" which doesn't add much filler. I have my doubts about the strength of that. For welding there's nothing wrong with a tiny gap IME. You can even fill quite a big one and get away with it if you have the welding skills to do that. But it's all about the fun and satisfaction of trying to do the best job you can which for me does mean improving fit-up.