The Nike cycling shoes I bought some years ago (at a steep discount when they got out of the cycling shoe biz) close with a ratcheting plastic strap rather than laces, so I bought a spare set of straps: the plastic part always breaks first. As it turned out, a coil spring inside each latch failed and the stub end (on the right side here) gradually worked its way between the latch tab and the frame:
Eventually this got to the point where the latches jammed and I had to do something. The first step was to drill out the rivet holding the spring and tab in place:
You’ll note the rich collection of swarf clinging to the drill bit, which indicates this one hasn’t been used since a lightning strike magnetized all the steel in the house. A pass through that demagnetizer shook off the swarf and prepared the bit for the next time.
Releasing all the parts shows the problem:
The OEM springs used 24 mil spring wire that, surprisingly, matched a box of music wire in the Basement Laboratory Warehouse Wing. The spring coils have 5 turns that just clear the 3 mm rivet that I recycled as a mandrel; I think a 2.5 mm pin would produce a better fit. Not being a fan of rivets, I replaced them with 4-40 machine screws, even though the threads probably won’t do the aluminum frame any good at all.
A protracted bending and wrapping session produced a reasonable approximation of the OEM spring:
It’s worth noting that each of those coils uses up about 55 mm of wire: 5 × 3.5 mm × π. Cut an excessively long piece from the music wire coil!
Trimming and shaping the ends to fit through the notches and around the outside of the frame shows that my wire-bending skills need considerably more practice. This spring (the second one I made) also shows that my beginner’s luck with the first coils wore off all too quickly:
But both springs fit and work fine, so I’ll call it done for now:
Will a replacement spring break before the plastic strap?
Obviously, I need a CNC spring bender…
The Smell of Molten Projects in the Morning 
Comments
10 responses to “Nike Cycling Shoe Latches: Resprung”
Nice job Ed, springs are tricky. If/when the 4-40 screw wears out, consider replacing it with a stainless version or making a tiny bushing from stainless hypo tubing. I keep some on hand for various things. This one from Amazon/SmallParts should work with 4-40s. http://www.amazon.com/dp/B000FN0TLW/ref=biss_dp_t_asn
They seem to be trivially easy in mass production, but I’m sure that’s after making a bushel of scrap while tweaking the machinery for best results. I should have made five and picked the best two, but … the first two worked well enough.
That’s even more wonderful than anything in my brass tubing stash! I’d probably just epoxy a short screw into each end of that tubing, call it a bushing, and be done with it. Thanks for the tip…
I bought a lifetime supply of stainless steel machine screws / nuts / flat washers a while ago and, ugly as it is, they’re in those latches. It’s nasty stuff to cut, but I love not having rusty screws.
Many (15?) years ago, the local surplus/used machine store had mixed stainless hardware for a couple bucks a pound (less than the scrap price for SS, no less). I bought a bunch and still have a good supply of SAE screws from 2-56 to 10-32 in various useful lengths. Add some black oxide socket head cap screws from the industrial supply house, and I’m pretty well set. Not much metric, but I do as little as possible. Short on nuts, but brass ones are readily available at Home Desperate. They work well with Locktite.
I grovel, I abase myself, I kiss your feet… you have stuff!
As nearly as I can tell, this area remains nearly devoid of good surplus outlets (Locals: P&T is OK, but not “good” because a 50 mile round trip lies well outside my comfort zone). That’s due to the paucity of manufacturing; IBM doesn’t do much of that any more and all the little shops round off to zero in terms of generating plentiful surplus.
Re surplus heaven: I got the SS hardware when I lived in San Jose. You could find anything from a silicon fab epi reactor to a 5000 pound 14″ shaper originally powered by lineshaft. Or, parts of even more exotic stuff. Now I live in Southern Oregon, where the surplus market stinks (with the rest of the economy). I can get a little locally, but I need to go to Medford (210 mile round trip, but it has a Costco) for harder to get stuff. Medford is home to a bunch of aluminum boat factories, so some stuff is easy to get. I have a bird feeder made from alum safety plate. :-) Unfortunately, surplus motors get destroyed by the junkies (liability issues, sez they), so I’m out of luck most times. Next time I go to Chicago, I’ll stop at Surplus Center in Lincoln, Nebraska.
BTW, locktite is catalyzed by copper, so that’s why brass hardware works really well with it.
That sounds like a working definition of “To be damned by faint praise”. [grin]
Er, not quite. :-) The presence of a Costco means that X times a year (5 < X < 8) we actually need to get to Medford, and White City metals is on the route. I do enough Useful Things (as defined by The Boss) with them to let me put metals in the budget. I try to make sure that Useful includes Fun, and then it's a workable arrangement. Ah, Trader Joes is opening next month. Must do an inventory….
A veil clears from my sight… now I get it!
Wow, I almost bought two pairs of my cycling shoes just because I love them so very much (hint – they’re pink) and wanted to make sure nothing would ever happen to them. You’re such an engineer!
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