Cutting an aluminium disc 19mm thick and 120mm in diameter is a piece of cake if you've got a suitable lathe, whether you start from a bit of 19mm plate or a 120mm diameter bar.
Not so easy if you’ve got a more modestly equipped workshop! And I wanted a square frame with a 122mm dia hole in it as well, anyway.
Coping saws aren’t really designed for metal cutting, but they can do the job as long as it’s only aluminium. Slowly...
The actual cutting took a total of just over two hours, but it made my arms ache so much that I couldn’t do it in one sitting. I spread the job out over three days, interspersed with other work. Perhaps surprisingly, the blade was still pretty much as good as new when I’d finished.
I’ve got a pillar drill and a 12mm drill bit I could use for those other holes!