In reply to Coel Hellier:
> I suspect that the article is not correct here in saying that 13.75 deg gives "consistent" holding power across the expansion range. You'd always get "consistency" so long as the cam spiral was logarithmic so always giving the same cam angle.
Yes, as long as the angle follows a logarithmic spiral, holding power will be consistent. As stated above, I believe Metolius change the angle part of the way through their surface to drop increase range a little at the end of the range of the cam. It's hearsay but I believe BD lobes are not truely logarithmic or at least at one time they weren't - take that for what it's worth, speculation.
> As for trade-offs, a smaller angle gives better holding power at the cost of lower range; a higher angle reduces holding power but has greater range.
Yes, higher holding power which is created by higher outward pressure on the sides of the crack. This is not a good thing when placed behind a flake! Same goes for Totem totems (rather than the basic) which actively increases this pressure. You just needto be aware of this when placeing. How much difference? Not enough not to buy them.
> Until recently BD had a patent on double axles, which is why DMM and WC have only now brought out double-axle cams.
Actually WC stuck to single axle for many years because quite a number of the management felt they were still a better product. New masters and a new way of thinking?
> Presumably softer metal bites better, but is less strong and less rigid, so the cam needs to be have more metal in it and so be heavier? (Hence, small cams, such as aliens and alien-clones can use softer metal but larger cams cannot.)
Exactly - as explained above. What counts for more here is the type of heat treatment of aluminium used. Most alu's in their O start (annealed) are soft and malleable. It's only when its been treated under specific regimes that it adopts its final strength characteristics. Often material will be bought in a treated state (it's more common), then cut to size, annealed, formed and then re heat treated. With heat treatment comes increased hardness (and eventually brittleness). Old Zero's used 7075-t6. Aliens use 6061-T6. Not sure what BD cams us but I would imagine its some form of 6000 series, mainly because they use extruded barstock which again, 6000 series is better for. But it's worth noting it's hard to devise a test to quantify the bite of the metal under realistic conditions as rock is generally not consistent, so tests are not truly repeatable. ou would only ever see a trend.