Excellent, thanks Alga. That means I can use the 1/2" (12.7mm) bit to drill the holes in the support plates instead of spending out on a 13mm bit. Will get these finished tomorow and hopefully have the SW's and plates welded!
Here's a pic of a few bits I made the other day (useless at remembering the names of parts and the book is out in the shed still!):
Amazing what you can do with a vice, a large hammer and a bit of brute force
Will those be sharp enough for the right angles? They should be far enough away from any crucial holes/welds but I always like to check.