Center for International Rehabilitation

Making Your Own Jigs

For those of you who are able to make your own jigs, this appendix includes a diagram and brief instructions for making each jig. Jigs can also be purchased ready made from Appropriate Technology International as part of the Basic Tool Kit.

PLYWOOD SQUARE 1) Cut a 12" (30cm) square piece of plywood. Check it with a carpenter's square to be sure that it is exactly square. 2) Cut the square in half along the diagonal. 3) Scribe an arc with a 4" (10cm) radius in the 90~corner of the triangle. Cut it out with a saber saw or coping saw.

SEAT BACK DRILLING JIG

1) Cut a 16" (40.6cm) length out of 1-1/4" x 1-1/4" x 1/4" (30mm x 6mm) angle iron.

2) Mark, center punch, drill five holes, and insert 3/16" or 7/32" (5 or 5.5mm) I.D. bushings as shown in the diagram. The hole size will depend on the outside diameter of the bushings you are able to find. If you are unable to get drill bushings drill 7/32" (5.5mm) holes.

3) On the other side of the angle iron, measure 2-1/4" (5.7cm) from the top end and cut a 35~ angle "V" as shown. The cut should also leave a shallow groove on the inside of the side of the angle iron that has the holes in it.

4) Place the end closest to the cut in a vise, and bend the long end forming a 35~ angle as shown.

BRAKE CATCH AND STOP WELDING JIG BRAKE MOUNTING HOLE DRILLING JIG 1) Mount 2-1/2" (60mm) "T" hinges on the edges of two blocks of plywood.

2) Make two 3/4" (18mm) cubes of solid steel. Cut a 1/8" wide groove in one cube and a deep "V" groove in the other. Drill a 5/16" (8mm) hole through the bottom of the "V" groove. 3) Weld the blocks of steel onto the ends of the hinges. The grooved sides should face down and run parallel to the backs of the hinges. 5) Place pieces of 7/8" O.D. tubing on the plywood. Bend the hinges until the block of steel is square to the plywood.

SEAT SUPPORT TUBE DRILLING JIG AND SEAT EDGE BAR DRILLING INSERT

MATERIALS

DIRECTIONS

1) Set the angle iron on the bottom plate. Using the hardwood block to hold the angle iron up at a right angle, tack weld the angle iron to the bottom plate, remove the hardwood, check the angle and finish welding.

2) Place the 1/4" (6mm) square bar at one end of the angle iron. Check that it is at right angles to the angle iron and tack the end in place. Check the angle once more, tack the other end and weld.

3) Measure and mark the angle iron as shown. Drill holes into which the 7/32" (5.5mm) I.D. drill bushings will fit tightly.

Cut a 1/2" (12mm) wide trough on the side of the hardwood block. The trough should be 1/4" (6mm) deep, and it should be centered as shown in the diagram.

X-BRACE WELDING JIG

MATERIALS

DIRECTIONS

1) Clamp the 22-1/2 inch (57.2cm) pieces of tubing to a very flat table, separating them by four inches by putting the four inch long tubes between them, as in the diagram. Clamp the 16" (40.6cm) tube square to one end of the longer tubes, with the ends of the longer pieces centered on the 16" (40.6cm) tube.

2) Tack weld the 16" (40.6cm) tube to the ends of the 22-1/2" (57.2 cm) tubes. Gas welding with steel rod is cheaper and quicker than brazing with brass and there is no

fear of cracking through fatigue, as would be the case for a wheelchair frame.

3) Check the alignment of the jig and bend the welds to straighten the jig, if it does not lie flat on the table. Complete the welds and realign the jig once more by bending it slightly if necessary.

4) Weld the rest of the pieces of tubing onto the jig as shown on the diagram. Make sure the tilted piece of tubing leans at 45~.

5) Weld the flat plates of steel on the ends of the 16" (40.6cm) tube. Set them at a 60~ angle to the plane of the jig.

6) Insert an accurately made X-brace, if it is available, to test the accuracy of the jig. If the cross piece of the X-brace is longer than 16" (40.6cm), put short pieces of 1" (25mm) square tubing alongside the ends of the bottom pivot tube of the X-brace. The short pieces should serve as spacers so that the jig can be used for a crosspiece of any length ranging in whole inches or 25mm lengths from 16" (40.6mm) to 22" (55.9mm) (see chapter 9). Make all adjustments that are needed in the jig with great care; if the X-braces made in this jig are not well aligned, the resulting chairs will not open or fold well and will be unlikely to roll easily.

X-BRACE CENTER HOLE DRILLING JIG

1) Cut a 16-1/2" (41.9cm) length of 1" x 1/4" (25mm x 6mm) bar. Mark the center of the bar and drill a 3/8" (10mm) hole.

2) If drill bushings are available, enlarge this hole to fit a 3/8" (10mm) I.D. bushing.

3) Grind off the ends of the bar at a 45~ angle. Be careful to keep the full 16-1/2" (41.9cm) length on the top edge.

SIDEFRAME BRAZING JIG

MATERIALS

DIRECTIONS

1) Weld the lengths of 1" (25mm) square tubing together as shown.

2) Weld the 5/8" (16mm) I.D. axle socket holding tubes on as shown. There should be 1" (2.54cm) between the centers of the top and bottom axle socket tubes.

3) Drill holes in the longest piece of angle iron to mount the caster barrels. Cut and weld on the pieces of 1" (25mm) angle iron as shown.

4) Weld the flat bar to the rear of the longest piece of angle iron as shown.

5) Attach the flat bar jig extenders with 1/4" (6mm) O.D. x 3/4" (20mm) long bolts and nuts. These are used when making a wheelchair with a 26" wheel. They are removed when making a chair with a 24" wheel.

6) Make a wooden clamp from two plywood blocks connected by a 1/4" (6mm) threaded rod or bolt.

HUB DRILLING JIG

This jig can be made for a hub with 40, 36, 32 or 28 spoke holes. Count the number of spoke holes in the wheelrims that you will be using before making your jig. The hub and the wheelrim must have the same number of spoke holes.

MATERIALS

DIRECTIONS

1) If a machinist is making this jig, ask her to make a piece with the following dimensions out of a single piece of solid rod or thickwall tubing, turned in a lathe.

2) If you are making the jig yourself, slip a 2" (5.1cm) length of 1-1/2" O.D. thinwall tubing inside a 3" (7.6cm) length of 1-3/4" O.D. tubing. The 1-3/4" O.D. tubing should have a wall thickness of 0.120". Tack the inner tubing in place to make a stop 1" (2.54cm) inside the jig. 3) The jig that will make a 40 hole hub must have 10 1/8" (3mm) diameter holes in each row. To make a 36 hole hub the jig will need 9 holes in each row; for 32 holes the jig will need 8 holes per row; for 28 holes the jig will need 7 holes per row. The first row of holes should be drilled 3/16" (4.8mm) from the stop (13/16" [20.6mm] from the end) and the second line 5/16" (7.9mm) from the stop (11/16" [17.5mm] from the end) as shown. Make two light lines around the tubing with a tubing cutter; one for each row of holes.

4) Drilling the holes so that they are evenly spaced around the hub is difficult. Color the end of the jig with a marking pen. This will help you see your scratches more easily. Set the vernier calipers at 0.550" (13.96mm) for a 40 hole jig; 0.611" (15.52mm) for a 36 hole jig; 0.687" (17.46mm) for a 32 hole jig; or 0.785" (19.95mm) for a 28 hole jig. Scratch a mark on the jig, measure around the jig with the calipers and scratch the next mark. Continue this process all the way around the jig. If the last mark does not match with the first, reset the calipers and try again until the distances between all of the marks are exactly equal.

5) Make the marks for the second row of holes exactly between each two marks in the first row.

6) Drill a 1/8" (3mm) hole centered on each of your marks. 7) After this type of jig has been used for awhile, the holes may become too large to locate the drill accurately. Dulling the side-cutters of the drill bit by spinning the drill between two pieces of sandpaper will help. Better yet is to put a 1/8" I.D. drill bushing into one hole on each row of holes. If your bushings are thicker than your tubing, let the bushings stick out on the outside of the tubing. Use these two bushings as guides for drilling all the holes in the hubs, as described in Chapter 11.

SPOKING BOARD AND RIM DRILLING JIG

This jig can be made for either 24" or 26" wheels.

MATERIALS

DIRECTIONS 1) To make a jig for a 24" wheel, use a compass to draw a 21-3/4" (55.2cm) diameter circle on the 3/4" (18mm) thick plywood board. (The rim of most 24" wheels has an outside diameter of 21-3/4" (55.2cm); measure your rim and change the size of the circle, if necessary). For a 26" wheel, draw a 23-3/4" (60.3cm) circle on a 26" (66cm) piece of plywood. 2) Draw two lines through the middle of the circle that are at right angles to one another. Mark the points where the four lines intersect the circle. 3) Drill a 5/8" (16mm) hole in the center of the circle.

4) Scribe a line in the center of each piece of angle iron. Measure from the bottom of the angle iron up two thirds of the width of the wheelrim as shown. Mark this spot and drill a hole that will fit a drill bushing. If you can't get drill bushings, drill a 7/32" (5.5mm) hole.

5) Use a vise to insert the bushings. 6) Drill 1/4" (6mm) holes in the angle irons and the wooden blocks as shown. Position these blocks so that the scribed lines in the center of the angle irons line up with the positioning lines on the board, and so that the front of the drill bushings are positioned at the three points on the circle. Clamp them in place and drill through the plywood board. Bolt the angle irons in place using 2" bolts (1/4" [6mm] diameter).

7) Using two nuts, mount a 5/8" diameter threaded rod (or 16mm, or 5/8" coarse thread reduced on a lathe to 15mm diameter) in the hole in the center of the plywood. Adjust the rod so that 2-1/4" (57mm) of the rod sticks up above one nut.

CASTER FORK BENDING DIE This die is made to be used with the Hossfeld type bender when bending the bar for the caster forks. 1) Cut a 1" (2.54cm) length of 2" waterpipe or other 2-3/8" (60mm) O.D. tubing. 2) Weld a 3/4" (19mm) I.D. washer inside the middle of the tubing.

CASTER FORK WELDING JIG

This jig holds the caster fork arms and pivot bolt in proper alignment for welding. If they are out of alignment, the chair will pull to one side. The following directions are for a jig which is easier to make than the jig that is part of the Basic Tool Kit. To make this jig, you will need to have one perfectly bent caster fork with the correct amount of caster fork trail (see Chapter 13).

MATERIALS

DIRECTIONS

1) Set up the Hossfeld type bender to bend a caster fork using the 2-3/8" (60mm) O.D. caster fork bending die. Insert the 13" (33cm) length of 1/4" (6mm) x 3/4" (18mm or 20mm) bar.

2) Starting the bend 3-3/4" (9.5cm) from one end, bend the bar more than 180~ until the two ends of the bar touch each other.

3) Remove the bar from the bender and pull the two arms of the caster fork open until they are parallel. Bending the bar too far and pulling it open will make a fork large enough to slip over the caster forks used in the wheelchair.

4) Using a 5/16" (8mm) bolt, mount the sample caster fork (one that has been bent correctly and that has 2-1/2" [6.3cm] of trail) inside the fork you just bent. Slip a piece of 5/8" (16mm) I.D. tubing over the caster fork bolt and lower it until it touches the outer fork as shown.

5) Braze the tubing onto the lower fork.

PIVOTING TUBE BRAZING JIG

MATERIALS

DIRECTIONS 1) Bend the bar in a vise as shown. 2) Using a hacksaw, cut the piece of tubing in half up the center. 3) Weld the round bar to the half circle of tubing as shown.

LOWER FOOTREST TUBE DRILLING JIG

MATERIALS

DIRECTIONS 1) Measure, mark and drill holes for three drill bushings as shown. 2) Weld bar to angle iron as shown.

STOP ROD WELDING JIG

MATERIALS

DIRECTIONS 1) Clamp the the one inch (2.54cm) length of 1/2" (12mm) square tubing on top of the 3" (7.6cm) piece of 7/8" tubing, flush on one end as shown. Weld them together. 2) Center and square the 3-1/2" (8.9cm) length of 1/2" (12mm) x 1/8" (3mm) bar on top of the square tubing. Weld it in place.

UPPER FOOTREST DRILLING JIG

MATERIALS

DIRECTIONS 1) Weld on the stop bar and cut away 3" (7.6cm) of one arm of the angle iron. 2) Drill a 5/16" (8mm) hole 2.5" (6.4cm) from the stop bar.

BRAKE COTTER PIN HOLE DRILLING JIG

DIRECTIONS 1) Cut a 1-1/2" (4cm) length of 3/4" (18mm) square solid steel. 2) Center and drill a 5/16" (8mm) hole lengthwise through the steel, and a 1/8" (3mm) hole 1" (2.54cm) from one end.

MOLD FOR SOLID RUBBER TIRE

This mold is designed to form solid rubber tires under heat and pressure. The mold can be made on a lathe by a skilled machinist from 2 disks of steel or aluminum 12" (30cm) in diameter by 1" (2.54cm) thick.

To make a tire uncured rubber is packed into the large groove and the mold is clamped between two heated plates. Excess rubber flopws into the two smaller grooves. The finished tire is stretched over a wooden or metal wheel (see chapter 12), bringing the tire to a full 8" (203mm).

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