Mary’s feet are exquisitely sensitive to irregularities in the insoles of her shoes, which poses a real problem with her bike shoes: those SPD cleat recesses are no good at all.
This is a view down into one shoe, with the SPD cleats adjusted all the way to the rear. That leaves a large recess in the front, which was painfully obvious to her sole. The white shape is the gap filler…
I pressed a sheet of paper across the gap to get the general shape, traced it twice onto a slab of 0.060-inch aluminum with a nice pebbly paint job, and cut the two pieces out. A few conversations with Mr Belt Sander, a few licks with a rat-tail file, and they dropped right onto place. The recess is slightly curved, but I didn’t have to bend the pieces to fit.
I laid duct tape across the whole affair, put the insoles back in place, and it was all good.
The backing plate is 0.072 inch thick and she was content with the difference.
In previous shoes, with the cleat near the middle of the adjustment range, I’ve stuffed epoxy putty into the gaps. That works, but it doesn’t bond to the (miracle engineering plastic) soles and tends to crumble. This is Not A Good Thing…
The Smell of Molten Projects in the Morning 
I hate the gaps in those shoes as well: entirely frustrating, especially if you step down into what you think is grass and find out is actually mostly water and suddenly you’ve a shoe full of irrigation. Since my shoes have absolutely rigid soles and I put some insole padding in, I sometimes daydream about epoxying a layer of fiberglass over the bottom of the formed insole, once it’s taken a set, and then rubber-cementing it into the shoe to form a perfectly smooth, nearly waterproof sole.
layer of fiberglass
That’s a great idea!
The trick would be getting it smooth while working inside the shoe. I’m pretty sure my glass-fu is nowhere near strong enough… but the next time Mary gets a shoe with a lumpy / pocketed sole, I’ll give it a try.
I wonder if you couldn’t put some glass and epoxy in, then have your subject… I mean the person you’re helping put a plastic bag over her foot and put the shoe on and stand on it to get it flat and form-fitted. A lot of higher-end bike shoes are similarly fitted to the feet of the purchaser these days, although I don’t think they’re using epoxy.
put some glass and epoxy in, then … stand on it
The list of failure modes for that operation is so ugly I just don’t want to go there…
In truth, an ordinary hot-mold footbed dingus might be the ticket. It’d add a bit of compliance, but we’re not high-performance racing wankers, either, so a bit of squishy wouldn’t make a bit of difference.
Next pair of shoes, we’ll give it a go.