Wish to flatten end (hammer) and drill 8mm hole. My fabricator says no, bloody hard to flatten, will work harden so hard to drill, and will stain. In lieu of using a canopy end fitting. What say the experts?
If you compress the end in a vice and press rather than hammering it, I wouldn't have thought that the flat surfaces would work harden so you should be able to drill it OK. I don't know about the rest.
If I didn't have an end fitting, I might drill the holes first, maybe 6mm, and flatten the tube by tightening a bolt and using a vice.
Then file or other wise open up the hole to size.
But I'm assuming light gauge tube, like swg 16 or 1.5mm
An end fitting is probably going to be neater!