Quote Originally Posted by WandrinAndy View Post
I had thought that the heavy version of the 45x45 would be strong enough as it is bolted along the back of it's whole length to 9.5 plate. I will look at replacing the top section with 45x90 then. Do you think this will be enough?
Nah even the heavy version isn't has strong as you think.!! The 45x90 will be better but I'd put it top & bottom and have the wide bit flat.
This way it ties into the sides better and gives more resistance to bending in lateral cutting directions.! It doesn't Add much to the vertical up & down strength plunging will inflict but the 10mm plate will help here and plunging should be avoided if at all possible anyway.! Most of the time the machines cutting and the forces are lateral.!!

10mm is just about ok for threading in Alu.