Inspired by the blog at www.pennyfakething.com, I chopped apart an old Schwinn Varsity frame and welded it back together along with some extra tubing and a BMX fork. This is a drawing I made showing roughly how the frame was assembled.
Almost 100% of the original Varsity frame was re-used in the final product, except for a few inches of unnecessary tubing. Props
Step 1: Cut Apart an Old Frame
The bike we cut apart was an old Schwinn Varsity. This was a good choice because these bikes are SOLIDLY made with thick steel tube which is strong and easy to weld. Also they are easy to find abandoned and rusting in your neighborhood dumpster.
Step 2: Half-assembeled
I didn't do a very good job of taking pictures during the welding process, but I hope this mid-welding layout explains enough.
The frame section connecting the old fork to the old down tube required the most fabrication. A plate of steel was welded between the arms of the fork, and a section of tubing (taken from the down-tube) was welded between it and the old down-tube. The fork ends were clamped together and welded onto what was originally the seat-tube. The angle of the fork's steerer-tube in relation to the ground (rake) is critical to the handling of the bike, so we just eyeballed it best we could.
A piece of scrap tubing was welded onto a bmx fork for the rear wheel. The front wheel is a 27in road wheel with 6-speed screw on freewheel.
The head-tube was flipped over so what was the top-tube in the original frame is now on the bottom. We did this to better use the angles that the top- and down-tubes come off the head-tube. We also removed the headset and put it back on upside down so it would still work with the crown race.
Step 3: Weld It Back Together
Here it is after the rear frame section has been welded together and the stem was welded upside-down onto the extra tube section between the fork/downtube. The bars were placed there so they are out of the way of your legs while on the bike.
The paint job is mostly to prevent rusting.
The initial design was modified because the center of gravity was too far forward, making the bike prone to flipping over forward when going over even small bumps. The weld connecting the rear tube to the BMX fork was cut, about 3.5in of the rear tube was cut off, and it was welded back together, which moved the seat back and put more weight on the rear wheel. The bike was much more stable after this.
Step 4: Give It Brakes, Gears, and Learn to Ride the Thing!
Here is (close to) the final incarnation. The original chain-guard was put back on and the brakes and derailleur are functional. You can't see the shifter in this picture but it is on the bars opposite the brake lever and is friction. Having gears makes this bike fairly hill-worthy and all-around more functional and fun. Especially since you can't stand over the pedals to use your entire weight!
The only thing that was changed after this was putting on a different saddle with built-in springs. Because of the location of the pedals it is nearly impossible to take your weight off of the saddle while going over bumps, which gave it a harsh ride. I don't even want to imagine what the original 'bone-shaker' pennyfarthings would have felt like without pneumatic tires, let alone springer saddles!
At first the bike is fairly terrifying to ride, but with a little practice it is actually quite stable (due to the inverse-pendulum effect) and tons of fun to ride. The mounting/dismounting is by far the hardest part. You have to stand on the pegs and get the bike coasting, then kick one leg over the bars and onto a pedal, then get your butt on the seat and swing the other leg around and past your hand. I will try to get a video of mount/dismount up here soon.
inverse-pendulum effect link