This uses the Broder System as its base:
Broder Height Extension and Post
4 x Broder Center Brackets
2 x 3" inch diameter White PVC 90 degree bracket
Jigsaw, String, Tape, Calipers, Pen, Tape Measure
Step 1: Marking the Bike Cradle Part 1
First, mark the 90 PVC fitting for the first cut using string. I chose to follow the preset markings on the pipe fitting.
Following marking on both sides of the pipe fitting. Use the jigsaw with an appropriate saw blade to make the cuts on both sides.
Step 2: Making the Bike Cradle Part 2
I suggest using strong to measure the distances along the curvature and to demarcate the true longitudinal axis.
Measure the distance between the two vertical brackets and mark these measurements along the axis of the halved pipe. I used calipers to measure the precise distance, but even then had to compare side by side the actual measurement due to the curvature of the pipe.
Using either a table saw or a jigsaw, start your cuts and readily compare the cut distances to the distance that is required between the 2 center brackets to ensure they nest well. You may need to file/double cut to make the slits in the PVC wide enough to nest well with the metal.
Step 3: Making the Bike Cradle Part 3
I suggest cutting the bracket right up to the perpendicular piece in as straight a line as possible.
Once cut, ensure that the bracket nests in a perpendicular fashion with the PVC pipe fitting.
At this point you may modify the depth of the cut in the PVC pipe to alter either the angle or the flush-ness of the bracket with the PVC. I cut the angle so that the PVC fitting slightly (5 degrees) directed the outermost lip upwards to act as a cradle to in case there was any slippage of the bike bar on the rack (i.e. slips towards the rack rather than away).
Lastly, I suggest using some pipe insulation to hide the slits on the interior surface of the pipe fitting. I reversed the insulation so that it held tightly within the walls of the fitting.
Step 4: Putting Everything Together
I recommend tying a rope around the spring bound portion so that when raising the rack you can pull on the rope while standing on the floor, then loosen the rope once into position.
I also recommend using a level to ensure the bar is straight up on all sides.
I have an old Y-frame so I have to mount my bike differently than a standard crossbar mtn bike frame. I think this rack design would probably work best for the latter frame type.