Justin started a thread about how to transit spring snow packs in VERY minimal shoes. Soft and flexible low-cuts. And I imagined having a stiff platform might (1) provide a way to have spikes and (2) provide more floatation. 32 minutes in the garage proved that, yes, you can have both those traits.
Let me just say: I'm not suggesting this for anything but low-angle snowfields and if you have exposure to downhill nastiness, then have self-arrest capacity regardless of what you have on your feet. Personally, I'd just wear stiffer boots and crampons in most cases, but I did find that a slight increase in area greatly decreased postholing.
Anyway, it's 5" x 15" of 5/8" T-111 plywood (because I had it lying around). The heel cup is cut from a steel can and the edges were smoothed on a beltsander and then covered with metallic tape. The heel cup is secured with 4 1-1/4" #7 sheet rock screws. Under the ball of the foot, there are 4 more such screws. And I cut four slots for a 3/4" x 36" nylon strap with a ladder lock fastex buckle. Here's the bottom:
The grooves are routered out of the bottom of the plywood. My thought was to have something akin to a Vibram sole and to resist side-slipping in softer snow.
I wore my softest, most slipper-like shoes (a pair of Merrill's slip-on low-cuts in mesh fabric) and tried them on undisturbed snow, shoveled-refrozen snow banks and the icy driveway.
In undisturbed, I got much less postholing (2-3") with the plywood than with the plain shoes (4 to 16"). In refrozen shoveled snow, neither sunk in but like on ice, I got much better grip because of the 8 screw tips pointing down.
400 grams for one. So not SUL, but it only took me 32 minutes to make and test. With tweeks and varnishing, maybe 1.5-2 hours and $8 of materials. So I'd be fine mailing them to myself just before the snowy passes and tossing them when not needed.
Tweeks: I'd add a heel strap. I'd varnish it so it didn't absorb water as readily. And I'd consider cuting an inch or so off the front because it would allow a more natural stride - less like wearing snowshoes. I used 1-1/4" #7 screws because my 2" #10s in stainless didn't have threads all the way up, but a little longer and a little beefier would have been better. About 1-3/4" in #8, 9, or 10.
Redesign #1: I'd laminate 1/8" door skin plywood onto 1/2" rigid foam to greatly reduce the weight. In other arenas of my life (boats, planes, treehouses) foam-core construction does wonders for weight reduction.
Redesign #2: Justin originally asked just about stiffening up the sole of his shoe. Using more surface area to get better floatation was my idea. 3/8" plywood cut just smaller than his shoe would provide a cheap set of 8-point crampons and weigh about 150 grams each. Way cheap.
Yes, I know it's a hack job. And not for everyone. I just wanted to see if the concept worked.
I was most pleased by the steel can heel cup. Strong, light and bomber - it got very strong once its bottom was screwed to the plywood.
Editted to correct typos.