Tube mitering is a fundamental part of custom frame building and I am sure there is always a need to be able to produce good results by hand and eye. Paper templates are a boon for speeding up the process and increasing accuracy but some time ago I decided to see how I would get on with some form of automation for the process. A milling machine, lathe or tube notcher can all be used but as I already had a lathe this seemed the way forward. Although I have since acquired a milling machine I feel the lathe is easier to set up for the process. I have described elsewhere making the tube blocks to enable this. My lathe is small with 500mm between centres.
I initially obtained several Coba-Tech hole saws from Stakesy’s metalwork machinery suppliers (https://www.stakesys.co.uk/hole-punches-hole-saws/hole-saws-arbors/coba-tech-10-tpi-fine-tooth-holesaws). These are fine tooth saws as opposed to the more usual coarse tooth saws I have used in the past. For cutting good mitres in fine tubes I would say these are essential and Stakesy’s were the only supplier I could find. Tube notchers are available, such as these: https://www.stakesys.co.uk/tube-notchers/tube-notchers. They are designed to be powered by a hand drill and are considerably cheaper than a lathe, though obviously are a one trick pony. The speed of the saws is set by the drill trigger speed and will be determined by feel rather than dials, but I am given to understand can be used quite successfully.