On small pipe, say 1" sched 40 and under, I don't cut any at all. Just butt it and weld it. This is just for structural concerns. Certainly, fluid or other applications where friction free interiors are important, I wouldn't use this, nor would I likely be using aluminum.
The other thing people are inclined to do with aluminum is, to set it up like a steel weldment and tack everything in place and weld it all at once. That may be fine of fixture/jigged parts, but aluminum moves an awful lot, especially once you start building 2D or 3D assemblies. You can end up with a potato chip in short order. I break them down into fully welded, "tweakable", sub-assemblies. In the case of this cooler caddie, I welded the bottom ring and the top rings, put their parts in and welded those first separately. Then, I added the 4 spacer tubes to the top ring, welded those fully and then re-squared, and plumbed everything before attaching that to the bottom ring. That way, there is only the 4 trapped welds of the spacers, which will move very little. That's what this photo is showing. The welded top ring with the 4 legs on it fully welded and then just tacked onto the bottom ring. No cursing, beating or banging. Strategically, those four small welds are in a good place for minimal distortion. Everything goes together so much more cleanly like this. Everything left is adjustable with the bump of a rubber mallet for fine tuning.
Everything then fits as measured and planned, with so surprises/further cursing.
This still gets 8 fishing rod holders and this will then plug into a trailer hitch on a golf cart so it gets a section of 2" 2" box under it yet.
, only don't follow the brown lines... )