Monday, August 1, 2011

Constructing a Diminutive Velocipede

This is something I've wanted to do for a while, and a week ago I bit the bullet and did it.

Required bits:
  • A 26" mountain bike

  • A 10" - 12" scooter or child's bike

Required utensils:
  • Hacksaw

  • Angle grinder

  • Some form of welder

Begin by cutting the front off the bike with the hacksaw, at the red lines shown below. Also, cut the handle bars shorter (I cut just inside the stock handgrips) and remove the stem that holds the handle bars in place. We'll weld the handle bars on directly for a more scale appearance.

Once you've done this, use the angle grinder to shape the stub of the stem so that it fits neatly with the shortened handle bars. Clamp the bars in the right position, tack weld them in place, and when you're happy with the alignment, weld them on. Remember to always clean any paint, rust etc. off the metal surfaces before welding.

Cut the seat post to length (I made mine around 100mm long), once again shape it with the angle grinder so that it fits neatly on the top of the down tube, and weld it in place. This geometry isn't very strong, so cut a short length of pipe (I got mine from one of the seat stays) and use it as a brace to support the seat post. You can see the seat post support propped in place ready to weld.

In order to get a better shape to the frame, I simply cut a wedge out of the down-tube (leaving it attached by a strip across the top) and re-welded it in place. In this picture you can also seat the seat post support properly welded in place.

Next, I needed a rear wheel. At the recycling station near work, I found a kids' 10" scooter which fit the bill.

It was a simple job to neaten up the cut end of the frame, cut off the scooter's front fork, and weld it in place at the rear. I'm still very new to welding, and the wall of the tube on the right is maybe 2mm thick, so I had a hard time making them stick without blowing a hole in the tubing.

You should now have something ridable, but the colour scheme leaves somewhat to be desired.

As this was to be prop for The Great Steampunk Affaire, bare brushed metal was fully appropriate. However, I plan to paint the frame black to prevent corrosion.

I'd initially planned for electric propulsion, but it ended up being quite practical to merely kick it along until I got up to speed, and then coast for a while. It was certainly a lot of fun on the night. :D

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