Hello phillip
Its prob best to use a metal cutting saw which can be set at different angles. If you haven't got one then the grinder and disc will have to do
He might have one. High angle cuts are a pain - you start needing a huge blade in order to reach through the stock. I don't think anything with a regular 12"-ish blade will come close to cutting that.
If you don't have access to a bandsaw that can mitre enough, it'll be following a drawn line with a plasma or cutting disc, I think.
Looking at the Rage-3 sliding compound mitre saw with multi-purpose blade. Do you think it would do acute angles? I am thinking about using a 45 degree jig to set up for an acute angle. I realise I might have to reduce the size of the tubing slightly from 4" but that would be ok.
Read the technical specs/manual, max depth of cut around 3" @ 90/90* for the compound mitre models. A 14"/355mm cut off saw will handle 4" @ 90 easily enough, mitre cuts up to 45*... depends on the brand (table/vice capacity and physical motor size- motor housing often hits stock before cut can be completed). Angles more accute than 45* reduce capacity even more