Making a tyre power hammer
Ian emphasises that he used plans sourced from Clay Spencer in the US, which are protected by copyright. The plans were inexpensive and detailed, as well as giving a list of materials. Crucially, plans and instructions were included for making the jigs which ensure that the frame and DuPont linkage are accurately put together. If you attend one of Mr Spencer’s weekend communal builds (called ‘hammer ins’) in America he provides the jigs.
The base is a 600mmx600mmx20mm steel plate. It provides the datum from which measurements and angles are measured. It was supplied by a local merchant cut to size.
The 2m tall section of 125mmx6mm RHS provides the frame, and was welded vertically onto the base. The hammer guide and its attachment to the frame were also 125mm RHS.
The trailer stub-axle and hub, sourced from Ashburton firm CM Trailer Parts, was welded at right angles to the frame RHS. An unused spacesaver spare wheel, which attaches to the trailer hub, was bought from a local car wrecker.
The support for the hammer guide was carefully welded to the frame at right angles, and the hammer guide welded to its other end, parallel to the frame.
A 25kg bar of mild steel, which forms the hammer, was milled flat on all four faces so that it just fitted the hammer guide. Slots to attach it to the DuPont linkage were cut near the hammer’s top.
The parts of the complicated DuPont linkage were fabricated, housings for bushes drilled, pivot pins turned up, and the correctly-rated coil spring sourced.
The anvil, formed from a round bar of 200mm diameter 1045 steel, was attached to the base by steel fillets. The anvil steel was the single biggest cost.
The 1.5HP single-phase electric motor had a self-cast aluminium wheel fastened to its shaft and was attached by a pivot to the frame, so that the wheel could contact the spare wheel’s tyre when the foot control was pushed downwards.
A brake for the trailer hub, wiring for the motor, the control linkage, and foot pedal also had to be made.
Ian says that the bill for the majority of the steel used was $1800, although this does include the cost of a small amount of profile cutting.