Using bar stool tops for your frame will be your undoing. They are not meant for this type of application. I am not going to recommend that you replace them, I am going to TELL you to replace them with a piece of 3/4" plywood. As an engineer I would hope that you understand that pieces of wood that are glued next to one another with no jointing will fail much sooner than sheets of wood stacked on top of one another and glued together with grain patterns switching directions every layer will.
When you start getting movement and heat inside that machine, the glue is going to begin to break down and the wood will begin to shrink and swell. I would give it all 2 months, tops, of working before your printer falls apart.
I would also suggest 10mm rods over the 8mm given the length you are working with. I learned the same thing the hard way when I build a large scale printer. Thicker rods are better.
When you start getting movement and heat inside that machine, the glue is going to begin to break down and the wood will begin to shrink and swell. I would give it all 2 months, tops, of working before your printer falls apart.
I would also suggest 10mm rods over the 8mm given the length you are working with. I learned the same thing the hard way when I build a large scale printer. Thicker rods are better.