Four-Passenger Coasting Bobsled: Iron-Shod Ash Runners, Hinged Rear Sled and Hoop Steering Wheel (Boy Mechanic, 1915)

"Any wood may be used for the sled, except for the runners, which should be made of ash." His list of materials: 1 top 6-1/2 ft x 16 in x 1-1/4 in; 4 runners 22 x 4 x 1 in; 4 crosspieces 16 x 3 x 1 in; 3 pieces 16 x 5 x 2 in; 1 piece 16 x 5 x 1 in; 1 shore 16 x 3 x 1 in; 4 seat backs 12 x 16 x 1 in; 1 dowel 3 ft x 1 in; 4 rods 5/8 in x 30 in; 4 eyebolts 1/2 x 6 in; 3 hinges 5 in strap; 8 hinges 3 in strap.

Cut one ash runner to shape and use it as the pattern for the other three. Cut a groove about 1/4 in deep along the under edge to take the curve of a 5/8 in round iron rod. Bend each rod to fit in the groove, up the back of the runner and over the top at the front; flatten the ends and drill two holes in each for wood screws (a blacksmith can flatten them, he says). Screw the irons on.

Notch the top edges of each pair of runners for the 16 x 3 in crosspieces, near the ends, so the crosspieces lie flush with the runner tops and the notches of each pair line up. Fit them snugly, fasten with long, slim wood screws, and stiffen each joint inside with a small metal brace.

Cut a heavy 2 x 5 in crosspiece sloping across its width, from 2 in thick at one edge to a feather edge at the other. Fix the three large strap hinges to the sloping face, and fasten the piece solidly on the rear sled's runners with its centre 8 in from their front ends. This lets the rear sled rock but not turn sideways.

Fasten the supporting crosspiece on top of the front sled's runners with its centre 11 in from their front ends.

Round both ends of the top board and plane it smooth. Underneath, fit two crosspieces, each with two 1/2 in holes bored through its width near the ends for the eyebolts: one with its centre 12 in from the rear end, the other 8 in from the front. Screw them on. Set the shore in the centre of the board, run wires over it between the eyebolts, and draw the eyebolts up until the wire is taut over the shore, so the long board cannot sag.

Round the top corners of the four backs and cut the bottom ends at a slight angle for a slant. Hinge them to the top board with the small strap hinges every 18 in, starting at the rear. Bore 1 in holes about 1 in deep in the edges of the top board every 18 in, beginning about 5 in from the front, and drive in pins 4 in long cut from the dowel, as foot rests.

Cut a broom handle to 18 in and fasten one end in a hole bored centrally in the 5 in crosspiece of the front sled. Bore a hole in the top board through the centre of the crosspiece underneath; put two metal washers on the stick and run it up through the hole, then fasten a hardwood collar to it just above the board so the top cannot lift off the sled. For the wheel, fasten a piece of wood across a nail-keg hoop, cover the hoop with garden hose and wrap it with twine; bore the centre of the crosspiece to fit the broom handle and screw it on.

Fasten the rear sled to the top board with screws through the free wings of the hinges into the crosspiece. Bore holes in the front ends of all runners and attach a chain or rope: the rear one's loop to the underside of the top board, the front one for drawing the sled.

From "Four-Passenger Coasting Bobsled" by R. H. Allen, in **The Boy Mechanic, Book 2**, Popular Mechanics, 1915 (Project Gutenberg 44585; checked on the archive.org scan boymechanicbook200chic2, pp. 24-26). The runner shape comes from his drawing, not from figures. The scan calls the steering collar a hardwood collar; the Gutenberg text drops "hardwood". The tools and metric figures are ours.