With the exception of stone, metal is probably the most difficult common material to work with, and one of the hardest things that needed to be done was to cut the tube at a reasonable 45 degree angle. The tool I had to use was a small, hand-held 350mm circular saw.
The initial plan was to cut each piece from the next at alternating angles (diagram, top) to minimize the total number of cuts. I needed to figure out a way to clamp down the stock at a fixed angle with respect to the direction of cutting. I ended up using part of a phone book placed on the edge of a table to lift the saw up to the top of the tube. Then I taped the tube to the table at the correct angle with the part to be cut hanging over the edge. I could then run the saw along the edge of the table and cut a straight line through the overhanging part. Long lengths were hard to clamp in this way, so I ended up chopping the stock into sections first (diagram, bottom). A table saw would probably have been the best tool to use for this.
- Use the right type of blade: Initially, the only circular saw blades I had were designed for cutting wood. I made a test cut to see if I could use it, but it just skipped across the surface and shredded the walls - definitely not appropriate. To cut metal, use a fine toothed blade with suitably hard edges. For thick metal, you may even have to use an abrasive blade.
- Measure twice, etc: I used a pencil to mark the places I wanted to cut, but this was hard to see against the steel. I wrapped masking tape along the lines to make it more visible. I also did a quick double check just before I cut to avoid stupid mistakes (ie, cutting on the wrong side of the tape)
- Perform a test cut first: To see how the width of your blade will affect your finished product. I also tried to leave a little extra material on the ends since it would be easy to sand down the ends a bit instead of having to cut a whole new length if it was too short.
- Use a high rotation speed and a low cutting speed: This will minimize the wear on your tool, and result in a better finish. There is really no reason not to do this, unless you are in a huge hurry.