Just curious. I have a distant in law with a spinal thing he was born with. We hit off, he and I, decades ago. He uses I think half crutches, the kind with a regular handle, but a leather strap about mid forearm rather than a padded knob in his armpit. When he has some width to work with, he can motate. Like on a driveway or sidewalk where he can swing the tips of the crutches wide as a pair, and move his legs as one appendage, his stride length is like 48-60 inches instead of the 28-35 inches most of us have on two legs. Indoors in a regular hallway he moves about as fast as anyone else, but he can outrun most of us outdoors on short courses.
He is hard on his equipment. He snapped another crutch a couple days ago, again, at the bolt hole for the handle, again, but this time the leather straps I made for the top bands (29 years ago) gave way too. He has a few bruises, didn't go to the ER, and I already have a new pair of leather bands ready to ship tomorrow. He strongly prefers wooden to aluminum crutches, we have shared several pints on that discussion over the decades. Typical off the shelf crutch for him is a glue lam of some unknown white wood.
I am wondering about upgrading his woodwork though. It makes sense that any species suitable for stick furniture (hickory, red oak) should be suitable for crutches, but weight is an issue. And they usually break (for him) at the bolt hole for the handle for his hands.
To make one pair of half crutches I am going to need four (riven) pieces steam bent into a gentle S curve, so air dried stock maybe nominal 1x2 by 60 inches long for starters. It seems to me walnut would be a possibility, walnut is about as strong as the oaks for impact, but weighs half as much; therefore gunstocks. I have never seen straight grained air dried walnut for sale.
Doug Fir could be done, but DF does not, at least at my house, stay strong around through holes without some volume and mass. I could get all the usual KD suspects at my local purveyor and do a glue lam with West system epoxy, likely 105 resin with negotiable hardener. I am moderately adept at using heat to increase depth of epoxy penetration in face to face joints.
Hardware is 3/16 inch. I am thinking about drilling the wood at 1/4 inch and using bushings. I could go a couple inches wide at the top ends of the S curved pieces where the through holes are, and then shape more narrow going lower.
What I want to do is get him setup for life in the next few months while I have the mental acuity to solve the problem, and the dexterity and strength required to execute the solution.
Local I can purchase, rive and air dry...birch. I am not sure which design parameters I need to look at regarding resistance to friction at metal fasteners and strength around drilled holes for through bolts.
Appreciate any and all input. If weight was not an issue, I got plenty of hickory in the shop. I don't even like hickory for axe handles because of the weight. Great axe haft, wears me out before lunch. He is on these crutches anytime he is standing- so looking for light, strong and tough. What I don't want to do is build something that might work and have my well admired inlaw in the ER with a broken bone if I am wrong.