I'm making a penny farthing, and it's going to be rad. I had already begun construction when Tim and Star convinced me to post an instructable about it, so I don't have original pictures of the first steps of construction, but I am creating some dramatization pictures to show how I bent the rim.
Step 1: Make the rim
Dramatization! Not actual footage!
So, I took a 4' diameter tabletop that was kicking around, and drilled a 1/2" hole near the side, and tied a bit of rope around it, as shown. Next, I laid my channel iron face down (the open side - the side you want facing outwards) down on the ground, put the table on top, looped the rope over the end of the iron (of which I had about 16'), and began to pull back as shown. This little piece of aluminum I'm using in the picture is obviously much easier to bend than the channel iron; be strong!
The steel will spring back a bit, so on a 4' table, I got about a 6' circle of steel. I stretched it down to be just under 5', cut and welded.
Step 2: See, look!
Isn't it great! Star thinks so!
Step 3: Welded
Here is the seam in the rim. I welded the outside and inside using a mig welder, and then ground down the welds. If you're going to grind down your welds on something structural like this, be SURE you got good melt-through with your weld.
Step 4: Make spoke attacher thingers
I took 6' of 3/8" steel rod, inserted the end into a hand brake with 1.5" sticking out, bent, then chopped 1.5" off after the bend, thereby making these little thingers. I then found a piece of crap about 1/2" tall to support them as I tack welded them to the inside of the rim as shown.
Step 5: The hub
So, I found a bunch of these. They seem to be feet from some optical equipment (or so Tim says).
So, go find some :-P