Originally Posted by
Nessism
I like tubemiter.exe
It works fine but realize that the template doesn't bevel the edges of the tube for a truly righteous fit. Plan on filing for a proper fit and hold the tubes up to a lightbulb to see how much light comes though between the tubes. The fit doesn't need to be perfect, but shoot high with your expectation for high pride in building!
The subject of bevelling is interesting actually. If you mitre with a holesaw the tubes fit together perfectly, but the bevel is the wrong way round for a good weld. In most places it's short enough that it doesn't make any difference-- it will all be melted in-- but it might be a bit longer on the "ears" of the downtube for example. It's better to actually knock that back a bit so you can get the weld in there better. The ideal is that the *inside* of the cut tube is touching the tube it's being joined to all the way around, and so it still ought to pass the daylight test. In an ideal world. It's still worth being able to weld across small gaps here and there if you need to. If practicing on offcuts, mtire some of them deliberately badly.