Jimbo wrote:
I'm planning to make some freestanding shelves from 15mm melamine
board(300mm wide). The boards will be joined with glued dowels.
What is the normal dowel diameter for a job like this? 6mm or 8mm?

I should think that 6mm dowels would be stronger as there would be
more "meat" around them. However, if you're relying on dowels alone
I shouldn't put anything heavy on the shelves! Could you get some
of those plug-in metal angles used in kitchen fitting? Would be
easier and stronger.