Hi Mactec - See attached dwg for Scoots tool plate dims. Frankies is longer. Scoots is 6mm S304 steel. I use SS as it does not need paint. Poor paint application has upset fits in the past so I don't use it much and SS works out cheaper then black steel painted.
Fibreglass pultrusion's are not very stiff in torsion so I'd steer away from these. My shed is made from lipped cold formed G450 sections as you describe. I have many offcuts that I look at occasionally and think I could do a machine with them!
A couple of things. If I use a std section I am limited to that section dims plus I have to get the holes done by a machinist which works out 2x or 3x the cost than laser cut holes. Std cold formed sections have poor dimensional control in terms of a machine build. If I get the section cut and bent I can specify flatness and fits for the critical features so I get what I want. If the part is not made to spec I can take it back and have it reworked or replaced. If I use a std section I can't do this. And the sheet metal parts work out cheaper then std sections drilled so that's the bottom line really. If a Maker buys a std section and drills their own holes that's another story but these parts are production parts so need to be able to be made in volume and to a spec.
I have recently settled on using 3mm galvanised steel sheet as its the lowest cost stiffest material. So to get thicker then 3mm the parts are laminated. Hence the I-beam for Frankies tool plate. I had it painted to get to the minimum order value & to add some bling, plus ordered some repeat parts for another customer... 3mm would be fine but Frankie is experimental in some areas so that's how it goes. I'm thinking about not bonding the tool plate together and start with the 3mm part to see how it goes, can always double up the part if needed. Onwards to more parts.... Peter