The hand cycle was transported from the airport to Midtown by a limousine driver a half hour later. When the driver opened the trunk, I had to ask him if this was the whole bike, or if perhaps we're missing the rest of it. I'd never seen such an alien unicycle-like contraption before. This was the whole thing, he assured me. He said he's done some unusual runs before, but this one probably tops the list. Once I got it down to the bike shop and examined it more closely, I deduced that it clamps onto the front of a wheelchair to turn it into a tricycle. I've worked on several hand cycles, but never this type before.
My heart sank a little when I examined the broken part; the non-drive crank arm was snapped in two. And this is no normal crank arm; it's made from the sawed-off hub portion of a normal square-taper crank with a custom arm welded on. It broke at the weld, an inevitable weak point.
Peacock Groove and Erik Noren would have it TIG welded back together in no time flat. But it's aluminum, and nobody I know is willing to do weld repairs on aluminum bike parts due to the tricky metallurgical complexities involved. The manufacturer, Stricker Handbikes, is straight out of Germany, and their website is only partially translated to English. I doubt they'll be able to help me out in the tight timeframe available. Thus far, no spare parts or loaner bikes could be located anywhere nearby, so I began formulating a plan. This was no normal bike shop repair; I would be spending my day off at TC Makers' Hack Factory, a shared shop space in South Minneapolis. They have the precision heavy machinery, and I have my personal collection of tooling and accessories. Time to make a part from scratch...
At about 11am Friday, I paid a visit to Amble's Machinery & Hardware and picked up a block of aluminum billet the size of a kleenex box. It was the smallest piece Jim had that would do the job, but it was still much larger than I needed, so I sliced off a piece in the bandsaw to work with. My hand is for scale; I don't normally put my hand in the bandsaw...
1-2-3 block, and clamped the block in the Bridgeport vice at an angle so the original crank surface was level. Then I machined the top perfectly flat and created two parallel flat surfaces on the sides.
adjustable boring head, measuring progress with a telescopic bore gauge and my favorite digital micrometer. I stopped when I was within a thousandth of an inch to check fit with the actual part. Too small; take another thousandth off. A perfect snug sliding fit!
Here's the mostly-complete part, sitting on the remainder of the billet from which it came. I have already drilled holes for pinch bolts to go through the stub of the new crank arm and to clamp down on the cylindrical old crank arm part. I would have made it lighter by taking off more material here and there, but I was running out of time.
I have to stress that this particular project is not the kind of repair we typically do at Freewheel, but we do have excellent resources and connections for when push comes to shove and the clock is ticking. If you need hand cycle repair work (that hopefully doesn't involve fabricating parts!) give me a call at Freewheel's Midtown shop and we'll talk options. 612-238-4447; ask for Karl.
Anna, I hope you enjoy the rest of your trip, and let me know how the bike performs!