HRS 2709/Bioe 2710 Wheelchairs I:
Fabrication Instructions

1. Cut top-bent tube long
2. Mark location of beginning of bend, and bend to specified angle
3. Cut bird’s mouth at front-end of top-bent tube, or use procedure described below (drill ¾ in hole, and bend out web) to support front-caster tube.
4. Cut front caster-tube receiver (1” ID)
5. Cut axle rail to specified length (longest portion on drawing)
6. Drill 2 3/4” holes at each end of tube through only one side of the tube. These holes reference the shortest portion of the tube (top, in assembled side-frame) which contacts the top-bent tube. They should be placed at the same radial angle as each other, and spaced in from the end so they cut out a portion of the tube that will ultimately intersect the top bent tube. The location of the center of the drill hole will be 3/8” (the radius of the ¾” drill) less than the distance where you would cut a wedge out of the axle rail to fit into the bend of the top-bent tube rail. (see rough sketch below)
7. Using the cutoff-saw, slit from each end of the axle rail tube to the ¾ in hole drilled (see rough sketch below.)
8. Using a screwdriver and pliers, bend open each end of the tube until the end is in the shape of a channel (see rough sketch looking from end below). After opening up the ends of the tube, confirm it slides onto the top-bent tube; use pliers to adjust as necessary. After bending is complete, use grinder or belt sander to round sharp edges (see rough sketch of tube with web bent out below) .
9. Cut seat-bottom pivot tubes from stock, adding 1” to specified longest length on drawing
10. As done above in the axle rail drill ¾” holes, this time all the way though the tube. Also, in this case, the holes should be perpendicular to each other and the bottom hole should be at the specified angle of the intersection with the top-bent tube. The holes should be spaced so the measurement from the inside-to-inside of each hole matches the dimensioned drawings.
11. Using the cut-off saw, slit both ends of the tube along the appropriate radial angle to intersect with the center of each hole
12. Using a screwdriver and pliers open each web at each end of the tube. As above, place ends over bent-top tube to assure fit. Use grinder or belt-sander to round sharp edges.
13. Cut stock for actual pivot point for seat (1” ID). Make sure top-end (with hole perpendicular to tube axis) of pivot tube fits snugly around stock…adjust pivot tube with pliers as necessary.
14. Cut stock for seat-back tubes to specified length on drawings.
15. Repeat 1-14 for second side.
16. Assemble both side-rails in jig using all pieces except seat-back tubes. Each side-rail and associated components should be put in the jig together and secured together to assure matching and symmetry.
17. Tack-weld each joint
18. Remove side-rails from jig, and complete welding
19. Place one side-rail back in jig, and position seat-back tube and secure with jig-fixtures
20. Tack and weld seat-back tube, and be sure to not change jig-fixtures.
21. Place second side-rail in jig and place seat-back tube in previously locked jig fixtures, making sure seat-back tube is on opposite side of side-rail. Thus, make sure you are making a mirror image of the first side-rail, not a copy.
22. Tack and weld seat-back tube.

1. Cut all tubes to specified length
2. Cut flat-bar to specified length
3. Use chop-saw to cut slit in middle of flat-bar starting and ending 1” from each end
4. Using flat-bar bending jig, and hammer—or arbor press, if available—bend flat-bar to form large U.
5. Place all pieces in seat-bottom jig and tack all joints.
6. Take seat-bottom out of jig and complete welding.

1. Cut stock to specified length
2. Bend desired camber using tubing bender. Be sure to start bend in correct place so center of axle will correspond to center of bend
3. Cut axle-nut insert tubes (1 ½ inch long)
4. Using a belt-sander or grinder (or lathe, if available) reduce the outer diameter of the nuts by rounding out the edges of the hex. Do this uniformly until the nuts slip snugly inside the axle-nut insert tubes.
5. Repeat with all nuts.
6. With two nuts on an axle bolt, slide into axle-nut insert tubes. Adjust nuts on the bolt so 1/3 of each nut sticks outside of the axle-nut insert tubes.
7. Weld each nut to the axle-nut insert tube
8. Remove excess weld with grinder or belt-sander
9. With axle-bolt still screwed into axle nuts and insert tube, slide into one end of the axle. Keep ¼” of the axle-nut insert-tube sticking outside the end of the axle, and weld.
10. Repeat 6-9 for other side of axle.

1. Cut bent-tube to specified length
2. Bend ends of tube at specified location to 90 degrees
3. Cut notch on inside of bent-tube at specified angle to the bends (45 degrees). This can be done in several ways. Ideally, a mill can be used with a 1 ¼ end-mill. Other ways include cutting a notch with a hack-saw or cutoff-saw (very carefully). A skilled welder can also cut this notch with a cutting tip. If a notch cannot be made easily, consider adding a gusset to support the bearing housing tube.
4. Cut bearing housing tube to specified length
5. Bore out each end of the bearing housing tube to allow snug fit or bearings. This can be done with a 1” drill or counter-bore. Be sure to drill into tube only enough for bearing to slide completely in the tube. If drilled too far, or for extra strengths, consider indenting the tube with the tubing cutter with a rounded roller (not the cutting roller).
6. Cut outer socket tubes to specified length.
7. Weld outer socket tubes and bearing housing tube to bent anti-tipper tube. Add gussets if needed.
8. Assemble caster bearings, casters forks, and caster.

1. Cut cross-tube to specified length
2. Cut notches in cross-tube with techniques described in (D3) or use gussets to support bearing housing tubes.
3. Cut bearing housing tubes and prepare for bearings as described in (D5)
4. Weld bearing housing tubes to cross-tube, assemble bearings, caster forks, and casters.

1. Cut two pieces of tube, one with 1” ID and one with 1 1/8 ID to specified length (3-4”).
2. Using cuttoff-saw, band saw, or hack saw, split both tubes, and set one set (half small and large tubes) aside.
3. Weld the remaining tubes in the following cross orientation:
   Rounded parts of each tube touching and tangent
   • Larger radius tube touching the midpoint of the smaller radius tube
   • Larger radius tube midpoint offset from smaller radius midpoint by 1”
   A rough sketch is shown .
4. Cut flat-bar to specified length, and drill ¼ holes where specified.
5. Cut ¼-20 all-thread to specified length
6. Bend all-thread around 1 ¼ pipe to make u-bolts
7. Assemble chair, and put welded portion of the fastener between the axle (larger radius side) and the axle-rail (smaller radius side). Be sure that the short portion of the larger radius side is toward the outside of the wheelchair. Use other large and small ½ of split tubes to put on top of axle and bottom of axle-rail, respectively. Pass u-bolts on top of the axle, and around the axle-rail to insert into the flat-bar on the bottom of the axle rail.
8. Tighten nuts on u-bolt to clamp the whole system in place.
9. With the fastener clamped in place, tack-weld the u-bolts to the top ½ tube piece places on top of the axle. Also, tack-weld the flat-bar where it touches the bottom ½ tube piece under the axle-rail.
10. Remove tack-welded fastener and complete welding
11. Replace system on assembled chair

1. Cut two receiver tubes to specified length
2. Cut two peg tubes to length. Drill adjustment holes according to drawing.
3. Cut a piece of plywood to the shape shown in dimensioned drawing for the foot platform. Drill out two holes in wood as described. Insert a peg tubes into the two holes in the platform so they are flush with the wood surface. Place a screw from the side of the wood through the peg tube to lock into place.
4. Weld receiver tubes to side frames (inside).
5. Drill one hole in receiver tubes for adjustment bolt.
6. Insert peg tubes into receivers and pass bolt through hole on both sides of the receiver and peg tubes.

1. Upholstery can be screwed to the seat bottom with self-tapping, or machine screws. A cushion needs to be added on top of the upholstery.
2. To setup adjustable seat-dump, use goniometer (or approximate) desired seat dump angle. Then mark bolt location (through slot in flat-bar) and drill ¼” hole with hand drill. Repeat for all desired angles (prototype has holes for 0, 10, 15 degree seat dump).

Seat Back

• Sling seat-back upholstery across seat-back tubes. Special seating systems can be bolted directly to the tubes if necessary.

Tube plugs

• Sharp tubes (at seat-back tubes, seat-bottom pivot, and front-caster tube) can be filled by fitting a piece of plastic or rubber into the tube.

Many methods to can be used:

1. use a lathe to turn down a piece of round-stock to fit a plug into the hole,
2. a grinder can similarly be used to turn down plastic or wood,
3. a router could be used similarly,
4. two pieces (one the ID of the tube, and another the OD of the tube) could be cut and screwed together to form the plug. Note that the plug for the front-caster tube can be made of metal and also act as the locking mechanism (below) for caster adjustment.

Front Caster-tube locking mechanism

After the wheelchair has been assembled, the front-caster tube should be rotated so that the caster bearing housing tubes are vertical relative to the ground. To lock this position, and also allow for adjustments (when different axles are used) a locking mechanism needs to be made using the following procedure.

With caster bearing housing tubes vertical on assembled chair, drill hole (large enough for 10-24 bolt through each side of the caster tube pivot point) through side-frame portion and caster tube portion on both right and left side of the chair. Drill this hole through only one web of the tube, and locate it in the center of pivot point tube on the side-frame.

Remove the caster-tube and open 10-24 hole into a slot around the radial direction. The slot length needs to be only 3/8” long. This will allow for the caster-tube to be rotated to accommodate various axles. This slot can be made in several ways:

1. drill more holes and use a file to connect the holes,
2. Use the cut-off saw to ‘slice’ part-way through the tube to create the slot,
3. Or, if available, use a milling machine…

To lock the caster tube in place, make a metal plug or insert with a 10-24 tapped hole that slips into the caster tube on both ends. To mark this plug, assemble the chair, and slide the un-tapped plug into the tube. Mark where the existing holes are that were drilled in 1) above, and drill and tap the plug.