Manual treadmills are relatively uncomplicated in terms of design. The running belt is supported by a deck that’s attached to a rectangular steel frame. The belt turns on rollers at the front and back of the frame. Flywheels at each end of the front roller provide resistance during workouts. The back of the frame rests on the floor and the front resides between uprights that connect to a handrail. Height adjustment bolts at the lower portion of each upright allow incline settings.
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Steel channel is welded to make the frame, and rigid conduit is bent to make the uprights and handrail. Rollers, flywheels, the deck and belt are obtained from a treadmill parts supplier.
Measure the width of the front and rear rollers, not including the threaded shafts at each end. Use a miter saw to cut two pieces of 3-inch-by-1-inch steel channel, 1/8-inch thick to this length. These are the front and back pieces of the treadmill frame.
Lay the running belt flat on a table or workbench. Insert the front and rear rollers inside the belt at each end and measure the length of the belt. Add 4 inches for overall clearance and cut two pieces of steel channel this length as sides for the frame. Weld one side and two end pieces together to make three sides of the rectangular treadmill frame. Make sure the 3-inch faces of the channel are facing out.
Weld the 2-inch-by-2 inch corner brackets at the open ends of the front and back pieces. Position them so the bolt holes can be used to attach the remaining side of the frame. Align the remaining side piece with the brackets. Drill 3/16-inch holes at the ends of the piece at each bolt location. Use 3/16-inch bolts with nuts to attach the side piece temporarily.
Mark the locations of the front and rear roller shafts on each side of the frame. Use an electric drill and 1/2-inch drill bit to drill holes for the roller shafts. Use a hacksaw to cut 1/2-inch wide vertical slots at each of the holes. Detach the removable side piece.
Place the treadmill deck in the frame. Put nylon washers on each end of the front and rear roller shafts. Insert the rollers into the slots on the welded side of the frame. Slide the running belt onto the rollers. Attach the removable side piece to the corner brackets with 3/16-inch bolts. Use the provided nuts and a hex wrench to secure the roller shafts to the frame.
Use the conduit bender with 3/4-inch diameter rigid conduit to configure the uprights and handrail. Drill 3/16-inch holes into the lower portion of the uprights for height and incline adjustment bolts.
Drill a 1/4-inch hole into each side of the treadmill frame near the front corners. Align the holes in the uprights with these holes and insert 3/16-inch carriage bolts to elevate the front of the treadmill. Hand-tighten the nuts for ease in changing the incline.