Attaching pi-brackets to field-frame bars[]
Begin by drilling 2 pairs of holes to each field-frame bar; these holes will receive the tenons of the pi-brackets. Unless the pi-brackets are of exactly identical dimensions, it's probably best to match the hole to each individual bracket. You should end up with a set like this:
Once the holes have been driller (or punched, if you've heated the bars), push the tenons of the pi-brackets through them:
Bend the tenons first slightly...
Then aggressively to lock them into place...