Tuning 3D printer is an infinite topic on its own. Let’s the fun part begin.

Rollers.

A central bolt of the roller of Piper 1 is at the same time tuning mechanism. To increase tension with the pipe tighten the central bolt, to decrease let it free. Rollers Should be sliding on pipes with a small tension. All ballbearing should rotate during the move.

Z axis.

After assembling the frame check that Z pipe is vertical. You may use any tool which allows measuring 90 degrees. Make necessary adjustments.

Make sure that Z rollers are tuned according to above instructions.
Untight top corner brackets on a pipe which is parallel to X-axis.
Move X gantry to the top position and temporary tie it to the top pipe (using rope or wire).
Tighten corner brackets.

Z Rods

If you already connected rods to Z motors couplings remove them.
Move X gantry to the lowest position and check that Z rods (lead screw/ACME screw) are aligned with motor shafts. To adjust alignment you may move motor left right.

Once rods are aligned with motors you may attach pineapple coupling.