It's been a while since the last technical post here, so this entry will have to cover a fair amount of ground. Looking forward at the project schedule, the critical path looks like this:
Validate "relaxing" shoe concept & finalize the last shape - scale lasts to prove grading ability - reliability testing - next round of user feedback.
Each milestone is broken down below.
Shoe concept: Originally, our designs were built on flat lasts. This meant that they had to tighten to transform into their aggressive state. As a side effect, we had tight control over the shape of the shoe in the flat state (since this was directly molded from the last shape), but getting the right shoe shape in the aggressive state was a matter of much painful trial-and-error.
After our first official round of user feedback, it occurred to us that the state we really care about is the aggressive shape. The shoe's relaxed state shape is less critical since most of our use-cases in that state are low-performance, i.e. warming up, walking around, belaying, etc. Therefore, the last shape should reflect the aggressive state of the shoe, and then it can relax from there. This change in approach is what I'm calling the "relaxing" shoe.
With seven last designs in the rearview mirror, I've been able to debug issues ranging from scaling problems (just how undersized should a last be for the shoe to fit snugly?) to appropriate heel shape (finally getting that suction-fit around the heel and Achilles tendon which lets me heel hook). Last number 8, which I'll laser cut the parts for this weekend, should finalize the toe box shape.
Grading and other manufacturing issues:
Once the entire last shape is refined, it'll be time to grade the lasts. Grading means producing CAD files (in this case) of a range of last sizes. Unfortunately this is not as simple as scaling the whole last by some amount. I've been messing around in CAD to find a suitable workflow for the grading and have a rough draft of Last No. 8 in Dan's size. If Last No. 8 doesn't need any tweaks, then I can proceed to cut it in Dan's size as well.
Additionally, over Thanksgiving, Dan and I visited Bishop, CA and visited The Rubber Room. Tony, Dan, and the rest of the guys there were amazing - letting me look over their shoulders while they worked on resoling shoes and sharing their insight into climbing shoe construction. Before I left, they looked over a shoe I'd built and gave me a couple of ideas on how to improve the rubber application process.
Reliability testing: The testing plan will need to fleshed out when this milestone draws closer, but for now, at least the following tests will be necessary:
- Abrasion on seams and on adjustment mechanism.
- Slip tests on locking mechanisms.
- Cycle testing between shoe states.
- Flexural cycling - cyclic loading.
- Flexural cycling - don/doff.
- Thermal cycling.
This will be very similar to the previous round of feedback conducted in Boston, but will provide a sanity check that all the feedback from last round has been addressed.