Another 3d Printer. But Better?

All my parts have finally arrived and it's almost time to start building. I bought the aluminum tube, smooth rods, and nuts and bolts from McMaster Carr. I bought the motors most electronics stuff just from ebay at low prices.

So the printed plastic part that is inserted into the square aluminum tube has been revised and now it can be tightened down and the screw pushes a ball bearing into plastic which expands. On the outside there are locking washers which cut into the aluminum and hold it in place.

I posted a few pictures showing my idea of how I'll be joining the square aluminum tube. I'll use expanding pieces that are placed inside the tube, as well as external parts that have a tight fit with no extra wobble space.

So far only sketched design on solidworks, and ordered the parts. Hope to start building in  a week.