Fitting the tubes....

Cross pieces are put in first to establish the stations. Then verticals are placed using a plumb bob to make sure they are exactly vertical. Of course, on the stations that have a plywood jig, I use that to establish the vertical.

Below is a little time saver. I used some scrap aluminum (cardboard would probably work better) to make a pattern since there were quite a few of the same cut on the 7/8ths inch tubes. Just place it around the end of the tube and use a silver pencil or sharpy to trace the pattern.

I tack each tube in as I go since this type of simple jig is not intended to hold each and every tube.