How to make a soapbox car

Written by laura reynolds
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How to make a soapbox car
Soap boxcar with wooden axles and cable steering. (Wikimedia Commons, Mission Museum Soapbox Derby Exhibit, Mission Museum photo)

Build a soapbox car and you're part of history. You're also a member of a select few who keep this hobby alive in an era of computerised controls and electronic games. The soapbox racer, like mumblety-peg and jackstraws, brings echoes of a simpler time when children created castles out of sand and race cars out of wooden crates. Today's soapbox racers are fabricated from more sophisticated materials, more often by men than boys and are entered in statewide and national contests.

Skill level:
Moderately Challenging

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Things you need

  • Plywood and lumber
  • Sheet metal or thin MDF
  • Hardwood
  • Eye bolts
  • Cable
  • Turnbuckles
  • Steering wheel
  • Four car wheels and two axles (available in sets or may be adapted from other uses)
  • Circular saw
  • Jigsaw
  • Adjustable wrenches, screwdrivers and hammer or mallet
  • Paint or varnish, brushes and buckets

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Instructions

  1. 1

    Build a historic replica or one of the more modern versions outlined below. The original racers were actually made of soap boxes---wooden crates that contained bars of soap wrapped in paper and packed in excelsior---with axles and wheels from old prams. Some were equipped like winter sleds, with straps tied to each side of the front axle that the driver pulled to steer his car; some were not and were steered by leaning and hoping. The most "luxe" models had bodies constructed of found lumber or sheet metal to shape the front and back of the vehicle in "streamlined" slants.

    How to make a soapbox car
  2. 2

    Construct the frame. Racer frames, originally built of scrap lumber, are made of plywood or composition board. Many racers choose an oval shape for their body for its aerodynamic efficiency and the frame is an oval board. The brake, if one is added, is a drag that lowers through a slot cut in the centre of the rear of the frame. Axle trees, or the channels for axles, are wood (hardwood will be less likely to split) boards that run across the frame, fore and aft. A channel large enough to fit the axle is grooved into the side that is attached to the frame and the edges of the trees are rounded and sanded smooth. The axle is inserted into this channel and the wheels are attached to the ends.

  3. 3

    Design the steering. Racers who add steering to their cars attach the front axle to the frame using a "king pin," a piece of pipe flayed open and drilled to attach to the centre bottom of the axle tree. The pipe is inserted through a hole drilled in the tree, bolted to the tree. It is then passed through the frame and secured with washers and a large headed bolt in the king pin. Drill a pair of metal straps and attach one to either side of the front axle tree, leaving a hole on each to which to attach the steering cables. Wrap these cables around the steering column so that they are pulled in turn to turn left or right. Alternately, configure steering without the wheel assembly so that the driver operates steering directly by pulling one string or the other to guide the car.

    How to make a soapbox car
    Steering wheel assembly.
  4. 4

    Put a brake in the rear of the car by attaching an arm made of wood to a pivot point and a cable to the front of the cockpit to pull it down where a flap of wood can serve as a brake pedal. Pull the brake back up with a spring suspended to the body.

    How to make a soapbox car
    Brake assembly.
  5. 5

    Build or attach a knife-shaped body to the frame, pass the steering column through a "dashboard" into the cockpit and the brake spring behind the cockpit. Attach a steering wheel, drop in a seat and off you go!

    How to make a soapbox car
    Body construction.

Tips and warnings

  • Weight should be kept low in your soapbox car to avoid tipping as it takes corners.
  • If you aren't experienced in building this sort of project, a number of museums and soapbox derby organisations offer free plans with complete specifications and parts lists.
  • Sand parts as you go and soften edges for safety as well as aerodynamics.
  • This is a great project for parents and children to work on together, but always insist on proper safety equipment (including safety glasses) for the workshop and racing (including helmets and pads). Set a good example; use tools safely and drive sensibly.

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