Lets Begin with the bottom quad frame.
Note: some of the pictures may not be 100% accurate as I was trying a few alternate configurations before settling on the current one.
Join a 258mm 3030 extrusion perpendicular to the 350mm 3030 extrusions using two Base Leg H26.8mm X4 parts. This becomes the front of our printer.
Use 4x 12mm M5 screws, through the leg and the steel plate bracket with T-nuts loosely connected. They can then slide onto the rail. Check it is square and tighten it down.
Connect 3030 corner brackets on the inside using 2x 12mm screws and drop in T-nuts
Next Loosely Connect the 380mm 3030 Extrusion across the bottom with 2x Corner 3030 Brackets on each side like the picture below. This is essential if you don’t have drop in T-nuts, but can still be a pain if you do.
The front face of the Crossbeam should be 180mm back from the front of the very front of the machine. If building in reverse config. The crossbeam should be positioned 250mm from the front.
Next Attach the remaining 258mm 3030 extrusion to the rear of the two 350mm extrusions using the two remaining Base Leg H26.8mm X4 parts, two plate brackets and two 30x30 corner brackets.
Check that the frame is square across all points and tighten down the legs. For the crossbeam, once measured at 180mm and squared tighten the 2x corner brackets on the back to lock it down. The front corner brackets on the 380mm crossbeam are still not tightened for now as we will need to remove them to finalize the z tower.
Attach another 30x30 corner bracket into the top of the crossbeam and the sides of the base on both sides and tighten them down.
Install the Y Axis Idler to the front extrusion centered in the middle with two 12mm M5 screw and T-nuts. Complete the idler using a 30-35mm M5 screw, M5 washers, stock or thinner aftermarket Idler pulley, and a M5 nylock nut. This part also requires 2 M3 heat-serts inserted on the front. This is used later to tension the belt. 2x 20mm M3 screws are entered into the heatserts.
Install the Y Axis Motor Holder to the rear extrusion approx 10cm from the left with two 12mm M5 screw and T-nuts.