Introduction: Crochet Aid for Wheelchair

An individual with an acquired brain injury who lacks the use of one of her hands has difficulty holding her yarn for knitting and crocheting. She also has difficulty dispensing her yarn without getting it tangled around her wheelchair.

Knitting is an activity known to distract people from pain, worry, and to provide a sense of worth, purpose and accomplishment. By engineering a device that can hold yarn and dispense yarn without tangles, this product will bring the therapeutic benefits of knitting to anyone, regardless of their physical abilities.

Reference Document Links

Requirements Sheet:

Competitor Analysis:

Final Decision Matrix:

Step 1: Collect Tools and Materials

  • Tools to be used in all parts of the project:
    • Black permanent marker
    • Ruler (metric or US)
    • Flathead screwdriver
    • Adjustable wrench

For detailed bill of materials, please go here:

Step 2: Printing the Clamps

  1. Download both clamp CAD files from Instructables page. Print both on a 3D printer.
  2. Use edge of scissors to clean out the extra filament from the tracks of the adjustable parts of the clamp attachments.
  3. Use sandpaper to round off sharp edges of both clamps. Be careful not to round edges too much so as not to sand into the hollow part of the clamp.

Step 3:

Using four 9.5” bolts, attach the dispenser clamp to left armrest of the chair. The should clamp fit snugly over the wheelchair arms.

Step 4: Sand Bowl

Using sandpaper, sand down any rough edges of the Tupperware

Step 5: Make Vertical Slit in Dispenser

  1. Using a ruler, measure 1 centimeter up from the bottom of the Tupperware on the outside of the bowl. Mark this length with a black sharpie. Measure 2 centimeters down from the top of the bowl, placing the ruler underneath the overhang of the Tupperware. Make sure this is directly above the first line marked, and mark this length as well
  2. Extend your lines marked to one centimeter in width. Connect them with sharpie in order to make a 1-cm wide rectangle
  3. Cut this rectangle out using scissors.
  4. If there are any sharp edges on the bowl once the slit has been cut, use the sandpaper to smooth them down.

Step 6: Add Set Screws

  1. Take the dispenser clamp base and put two set screws into the holes on the top of the clamp base
  2. Take the bottom slider of the dispenser clamp base and put two set screws into the holes on the top of the bottom slider

Step 7: Screw Down Dispenser

  1. Place the bowl on top of the top layer of the bowl clamp, and center it how desired. Note the positions of the four small holes on the clamp; these are for screws.
  2. Using marker, make a dot on the bowl in the four places where the bowl overlaps with the screw holes on the clamp. Remove the bowl from the clamp
  3. Using an office tack, poke four holes in the plastic of the bowl in the four locations marked
  4. Place four .6-cm long screws into the four holes, and place the bowl back over the tray in the same orientation as before
  5. Tighten the screws using a screwdriver

Step 8: Slide on the Dispenser

Slide bottom slider onto the dispenser clamp base. Then, slide the top slider (with the dispenser) onto the bottom slider.

Step 9: Prepare Tray

  1. Use a vertical bandsaw to cut off the curved sides of the lunch tray, leaving four straight sides. Make sure to cut straight; there will be excess material on each of the corners.
  2. Grind down the excess corner material using the sander. Once the corners have been worn flat, carefully round them to prevent sharp corners.

Step 10: Make Cut-Out for Wheel

  1. Place the tray against the wheelchair you will use this for, in the location you wish to use it. Using a black sharpie or another permanent marker, trace the outline of the wheel where it covers the tray.
  2. Use a vertical bandsaw to cut along the circular line you drew
  3. Use a sander on each edge until all plastic flecks and sharp edges have been worn smooth.

Step 11: Drill Holes for Bolts

  1. Place the tray in front of you with the cutout for the wheel on the top left.
  2. Place the side of the hinges with the second hole on the left against the tray five centimeters from the bottom left corner. The top of the upper hole of the hinge should be three centimeters from the bottom of the tray.
  3. Using the sharpie, make a dot in each of the three holes.
  4. Keeping the hinge in the same orientation and on the same level, move it seven centimeters to the right. Before you mark these holes, double check that the space between them is equal to the space between the hinge holes on the second clamp. Once you are sure this is the case, mark these holes as well.
  5. Use a drill press to drill the six hinge holes, in the locations you marked in the previous steps. Use a 26 drill bit moving at 2000 rpm to make these holes.

Step 12: Preparing the L-bars

Using a vertical bandsaw, cut the L-bar into two pieces, one 25.5cm and the other 37.5cm.Using a sander, sand the upper corners of both pieces until they are smooth and round.

Step 13: Attaching the Bars

  1. Place the tray down so that its underside is facing up, and the cutout for the wheel is on the upper right
  2. Place the longer L-bar diagonally on the tray, with the unrounded corners pressed against the tray itself.

  3. Place the shorter L-bar against the left side of the tray, with its unrounded corners pressed against the tray itself

  4. Mark the spots where the rivets will go with a permanent marker on the bars. - For the longer bar mark five places equally spaced apart. For the shorter bar, mark four.

  5. Drill out the spots where the rivets will go on the bars, and drill holes into the tray, using those drilled bar as a template

  6. Using a rivet gun, attach the pop rivets against the bar and tray.


Cover the top of the tray with Dycem - Use super glue to adhere the Dycem to the tray

Step 14: Attach Hinges

  1. Attach the hinges to the tray holes drilled in step “j” using three 1-cm long bolts for each hinge. Ensure these bolts stay in place by attaching a 12.7mm hex nut to the bottom of each bolt.
  2. Attach the other side of the hinges to the holes 3D printed in the tray clamp created in step two using three 1-cm long screws for each hinge.

Step 15: Attach the Tray Clamp to Wheel Chair

Using four 9.5” bolts, attach the tray clamp (with the tray attached) to the right side of the chair

Be sure to tighten all bolts.

Step 16: Optional: Add Dycem to Clamp

If the clamp is able to rotate around the armrest when force is exerted onto the tray, you can add Dycem to the inner walls of the tray clamp minimize this problem. Do not add the Dycem to the wall touching the top (cushioning) of the armrest as this will make it difficult to get the clamp on the armrest. You can add the Dycem to the other three walls that touch the armrest.

Step 17: Improvements and Extension Projects

1. Work on aesthetics, especially around the tray. Give the device a more polished, finished look.

2. Make the clamp stronger by adding layers of filament inside the printed shell.

3. Make the tray less intrusive on the chair and easier to pull upwards.

4. Make a tray cover so that the Dycem does not wear out over time, as well as for aesthetic purposes.

5. Use wingnuts instead of hex nuts within the design, in order to make the clamps easier to remove and adjust.

Step 18: Resources and References

OnShape CAD Software

Mr. Brunner

Ms. Curran

Professor Stafford

Zach Boyer