Folding Carbon-fibre crutch
My sister-in-law is mobility impaired and has to use a crutch which is not particularly aesthetically pleasing, quite heavy and has bits sticking out (the nuts and bolts) which tend to catch on things (see Fig 1, left). The main problem with it is that it is cumbersome and gets in the way when it is not being used. I set myself the challenge of designing and making a crutch which would fold in half (to be more easily stored), be very lightweight and have a sleak, attractive design. This page details the result (see Fig.1, right), which I gave her as a Christmas present in 2003. It is not a guide to how to make one, but might be useful if you want to try something similar yourself. Note: this design is for a custom-made crutch – it is not adjustable for diffferent people.
The crutch folds in the middle (see Fig. 2) by the user squeezing together the two upper rods and pulling the two halves apart. The crutch is held together with bungee cord running inside both rods. To put it together again, the rods are squeezed slightly and pushed into the brass ferrules (see below for more details).The bowing of the rods keeps the whole thing rigid.
My sister-in-law was pleased with the final result. Unfortunately, the crutch was broken a few months later, ironically because of its unobtrusiveness. She had folded the crutch and put it on the floor by her chair when she was in a meeting and somebody accidentaly stepped on it and crushed the tubing. In hindsight, I would use thicker walled tubing which would be much stronger.
I took measurement from her existing crutch of the block that fits under the arm and cut a piece of wood to size. I drilled two holes half-way through for the carbon-fibre rod. The holes were of a size to ensure a tight fit with the rods. I pushed the rods in and reinforced the joint by hammering in nails through the wood and rods (after drilling a pilot hole). See Fig 3.
Next, I measured the size of the handle and cut a block of wood to size. I cut two holes through it for the rods. This time the holes were slightly oversize to allow the rods to go through at an angle. I whittled down the block to make it more rounded. I slid the handle along the rods until it was at a comfortable distance from the top block and then glued (with epoxy glue) and pinned it into place (see Fig. 4).
For padding, I cut a piece of pipe insulation to fit the handle (see Fig.5).
The hardest bit was next – how to make it fold easily but still remain rigid when put together. The solution I came up with was as follows:
I cut the rods about halfway along. I bought some aluminium tubing that was a tight fit in the bore of the rod and some brass ferrules that were a tight fight around the outside of the rod. I cut some of the aluminium tubing and glued it inside the ends of the (upper) carbon-fibre tubing, with a few centimetres sticking out. I glued the brass ferrules onto the ends of the (lower) carbon-fibre tubing, with a few centimetres overhanging the end of the rod. I threaded bungee cord from the very top of the crutch to the foot and secured it at each end. See Fig 6.
Next, the ends of the rods were pulled together and cut so that the overall length of the crutch was correct. The rod ends were drilled and wired together. There is a lot of force pulling this joint apart (because of the bowing of the carbon-fibre rods), so they have to be secured together very firmly. See Fig. 7:
Finally, a rubber foot (from a hardware store) was pushed onto the end (Fig. 8).
One of the aims I set myself was to minimize the weight of the crutch. I measured the weight of the individual parts:
- carbon fibre rods: 46g each
- top block (wood) 55g
- handle (wood) 22g
- rubber foot: 30g
- aluminium tube 6g each
- brass ferrules 14g each
Total weight was 240g.