Im looking to use some mild steel box section for a base/support table for a diy laser cutter. The only steel I have had experience with so far is prob from the cheaper end of the market mild box steel. We have been using it to build agricultural machines. Its quite straight but for my laser im looking to buy some steel that is as straight as the aluminium profiles you can buy from Bosch or Misumi. So my question is how do you classify different grade of steel and where is the best place to start looking for high end engineering type material.

Gav