I don't use jigs and plans. The closest. I came to a plan or jig, is the large sheet of cardboard on which I drew some lines to get the angles reasonably correct. The frame came out nothing like the cardboard drawing, things tend to change as you progress, think of different design considerations and so on. To get sizes and angles, I set up some bricks and a couple of boards in a seat shape, sat down and got the wife to measure with a tape measure and angle finder. For the lumbar support, I took off my shirt, leaned back against the board and got the wife to trace the shape of my back against another board to my side with a permanent marker.
For pedal to seat distance, I sat on the makeshift seat, lifted my foot up another 150mm. And got the wife to measure between my instep and where the squab meets the seat back.
Jigs are great when manufacturing things in quantity, for one offs, I find they are not of much use.
Incidentally, make sure your heel is well clear of the ground when setting the crank height. An easy thing to miss, so I found on earlier builds. That will dicatate the height of the seat also, unless you change the seat height to crank height ratio. I think my builds were all around 100mm to the bottom of the chassis. I opted for the lowest seat height I could get to aid handling.
On my very first build I only had rear brakes, Big mistake, rear brakes on recumbents simply do not work at all. When you apply brakes, all weight is transferred to the front wheels, making rear brakes pointless. I also fitted a flat board seatback on the first build - Oh, my aching back, also wore the skin off covering my backbone. Not recommended at all, unless you have a mesh seat or a well padded seat back. I used a joystick steering system on the first one, it worked great, but, nowhere to place brake levers and gearselectors, so I had to weld a tube off to the side to mount brake levers and shifters on. On the plus side, this red one was extremely fast, the only thing stopping me going faster was the relatively low gearing.
