Center for International Rehabilitation

Appendix A Making Your Own Benders

BENDER FRAME TO USE WITH HOSSFELD DIES

As was mentioned in Chapter 2, we recommend that you purchase the dies for bending tubing, bar and rod from Hossfeld. These dies are used in a bending frame that can be built by a skilled mechanic. If you'd rather not make your own frame, you can order a frame, with the dies, either from Appropriate Technology International or directly from Hossfeld.

The bender frame has two main parts: an outer arm that is bolted to a heavy wooden work bench and an inner arm that pivots inside the outer arm. Each arm is made up of two steel bars with a precise pattern of holes drilled in them. The pattern of holes drilled in bars forming the outer frame is different than the pattern of holes drilled in the bars forming the inner frame.

To make the bender frame, you will need a couple of tools that are not used in making the wheelchair: a 3/8" tap (for cutting threads) and 5/8" (16mm) and 3/4" (19mm) drill bits. This bender has been designed using English dimensions. Since the dimensions of the bender frame must be precise for the dies to bend tubing without wrinkling it, there is some risk in building the frame using metric measurements that are only approximately equivalent to the English. For this reason we have not given metric equivalents for most of the bender dimensions.

MATERIALS

DIRECTIONS

1) Carefully mark and center punch each hole in the locations given in the diagram. Make two identical inner bars and two identical outer bars.

IT IS VERY IMPORTANT THAT THE HOLES ARE LOCATED ACCURATELY! If they are off 1/16" (1.5mm), your tubing is likely to kink when you try to bend it. (See Chapter 6 for directions on how to drill holes accurately.)

2) Drill a starter hole at each mark using a center drill; finish drilling all the holes with a regular drill bit.

3) In one of the outer arm bars, thread the two 5/16" (8mm) holes with a 3/8" (10mm) tap (thread cutter).

4) Cut four spacer tubes from 3/4" waterpipe (any thickwall tubing with an outside diameter between 1" (25mm) and 1-1/2" [38mm] will do). Cut two of these spacer tubes 3" (7.6cm) long and two 4" (10.2cm) long.

ASSEMBLING THE BENDER 1) Mark and drill three 1/2" (12mm) holes in the corner of a heavy wooden work bench. Use one of the outer frame bars to locate the holes. When the frame is mounted, most of it must stick out beyond the work bench. Consult the diagram to see about how far the bar can stick out beyond the work bench.

2) Begin by assembling the inner moveable arm of the frame. Bolt the two inner frame bars together using the 5" (12cm) bolts and 3" (7.6cm) spacer tubes. Note that the bolt on the end does not use a spacer tube.

3) Assemble the outer arm of the frame using the 8" (20cm) bolts and 4" (10.2cm) long spacer tubes; bolt it to the work bench as shown. The frame bar with the 3/8" (10mm) threaded holes should go on the bottom.

4) Connect the inner and outer arms of the frame to one another using the Center Pin and Center Pin Support Plate (or a standard series 1/2" [12mm] I.D. washer) as shown.

The Center Pin and Center Pin Support Plate can be purchased from Hossfeld; they are also included in the Basic Tool Kit.

Attach the Center Pin Support Plate (or washer) with a 3/8" (10mm) bolt that is 1/2" (12mm) long. Screw the bolt into the threaded hole located next to the center pin. The edge of the washer or Center Pin Support Plate will catch the Center Pin preventing it from sliding through. 5) To make the bender more easily usable by many disabled people, mount an auto jack on it as shown. The jack is the type used on most large U.S. autos; a 1/2" (12mm) diameter hole must be drilled in the end of the jack to mount it on the bender.

MAKING A WOODEN BENDER AND DIES

This bender has been designed to make large radius, gentle bends for the handrims and the fenders.

MATERIALS

DIRECTIONS

1) To make the bending dies, use a saber or coping saw to cut one 23" (58.4cm) diameter circle for fender bending and one 15" (38.1cm) diameter circle for handrim bending from a sheet of 3/4" (18 - 20mm) plywood (or longer lasting hardwood). If you are making chairs with 26" wheels, cut a 25" (63.5cm) circle instead of the 23" circle for fender bending. Cut each circle in thirds to make three dies.

2) Cut a bending chock from a piece of hardwood. It should measure about 3" x 3" x 3/4" (7.6cm x 7.6cm x 2cm). Use carriage bolts to mount the bending chock on an 18 inch (46cm) square piece of 3/4 inch (18-20mm) plywood as shown in the diagram. The grain of the bending chock should run toward the bending die. 3) Bolt one fender bending die to the square of plywood as shown, leaving 3/4 of an inch (20mm) between the bending die and the chock. If the bending die is made of hardwood, point its grain toward the chock. Remove the fender bending die and mount the handrim bending die on the same three carriage bolts.

Table of Contents