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Tubbs Flex Alp failure

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  • #16
    It's nice to have the engineer's perspective TB. The crampon is, in fact, bent as you noticed, but this is by design. The crampon is produced this way (I had assumed) to conform better to the shape of the boot and ease of walking?

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    • #17
      Like FlyfishingandBeer said earlier, and TrailBoss just pointed out, the metal is questionable. FlyfishingandBeer said that carbon steel has a weight advantage over stainless. So there you go. The manufacturer is choosing weight over durability. I believe the moral of the story is that if you want trouble-free snowshoeing you choose stainless steel over carbon steel, but the product will be heavier. Now if you just want snowshoeing for today, you're probably ok with this scenario. If you want to keep using your snowshoes long after the warranty, well, carbon steel could be a problem.
      Last edited by CatskillKev; 03-01-2017, 06:23 PM.
      I might be kidding...

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      • FlyFishingandBeer
        FlyFishingandBeer commented
        Editing a comment
        I may have to correct myself on what I said about their weight properties. I got curious about what could be causing these issues and did a bunch of reading up. Most of what I found is pretty inconclusive unless you speak scientist, but here's some Cliff's notes. There's four different types of carbon steel and they all have slightly different weight and density properties. What I'm gathering is that the advantage to using carbon steel is that its harder than stainless steel and easier to sharpen and keep sharp. The downside is that is more brittle and depending on carbon level will almost definitely have a life span. Its starting to appear that the shape, thickness, and overall build quality are the largest variables with these failures. Naturally, frequency and nature of abuse on the product matters as well, but mostly for trying to determine when the failure will happen, not if the failure will happen. I believe this is why we're seeing this issue on the LG Blizzards and Tubbs Flex Alps, but not the Evo Ascents or Flex TRK's.

        Also, as bud said, he wasn't able to drill through his Flex Alps so it sounds like they might be using an actual high-carbon steel rather than some powdered knock-off like I had originally suspected. This is great in terms of traction and ensuring that the crampons don't start flattening out over time, but they're certainly going to be brittle. Especially in extremely cold temps over harder ground.

      • CatskillKev
        CatskillKev commented
        Editing a comment
        So maybe I should retract what I said then. :-) There are invisible factors in metal, but although stainless is more expensive, we cannot be sure that stainless is better, except in rust prevention, which doesn't seem to be the issue in these young snowshoe problems.

    • #18
      Let's compare the Flex ALP snowshoe-crampon to a garden-variety 12-point crampon.
      • Crampons are typically made of high-carbon steel (and of stainless-steel and even aluminum).
      • ​The points are on the order of one and quarter inches long and about 3/16" thick.
      • ​At their widest point they're about 5/8" wide.
      ​Basically they're long slender teeth that are subjected to a lot of abuse but rarely fracture or break off.

      ​Compare that to the teeth on the Flex ALP crampon. I don't have one handy for measurements but (from photos and memory) they appear to be longer and broader. That means more leverage and contact area so the forces acting on them are greater. Given teeth the size of soup spoons, the material will need to be either thicker or stronger than on a full crampon.

      ​In contrast, the MSR Evo and Tubbs FLEX TRK use, in effect, one wide serrated "grabber". There's a lot of metal in play and, although not impossible, I've yet to hear of the entire front end snapping off.

      Looking for Views!

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      • Trail Boss
        Trail Boss commented
        Editing a comment
        The more I think about it, it reminds me of an aggressively serrated knife (or saw blade). The metal used to make these MSR crampons is surprisingly thin. I suppose they discovered serrating the end ("half-teeth") was stronger than making four individual (and longer) teeth.

        I also noticed that on other MSR models, like the Lightning and Revo, they use two long front fangs. However, the two fangs can move independently. I wonder if this was done to prevent fracturing if they were connected together? The fracture that occurs between the ALP's two front teeth seems like the result of the teeth being subjected to unequal forces (i.e. they attempt to move independently).

      • CatskillKev
        CatskillKev commented
        Editing a comment
        I don't think that's it. Think of the 2 front teeth in the flex alp as a bridge, just like the 4 teeth in the MSR as a bridge. Well, the Alp bridge is cut out by the deep gouge in the middle, so the bridge wants to sag and pull apart. I think this pulling apart could be happening in normal use, even with plenty of snow. The weight of the user is trying to make the bridge sag and open up between underneath. Of course there is no opening force on the top, just underneath. The flex alp has a weak bridge.

      • Trail Boss
        Trail Boss commented
        Editing a comment
        With all due respect, I wouldn't pitch that "saggy bridge" theory to a mechanical engineer unless I supplied many, many beers beforehand.

    • #19
      What do you think is acting as the strength to hold up the user? Shoes with axles use the axle. These types have to use the rigidity of the crampon to hold up the user. The crampon is more rigid at the teeth, so I'm thinking that is the area that is supposed to support the user. Admittedly its a bit far forward, so who knows.
      I might be kidding...

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      • Trail Boss
        Trail Boss commented
        Editing a comment
        Prolly bones and muscles.

      • CatskillKev
        CatskillKev commented
        Editing a comment
        Maybe you're right. An argument in your favor is that I just happened to write to gv today and just found out the axle in the 12x42 is aluminum, and it has not sagged on me yet, so maybe the stresses are not as great as I thought.

        I did break an axle once on a Tubbs Katahdin, and they switched out that axle, which I believe was aluminum, with a stainless steel one.
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