NNN BC - faith somewhat shaken

[lilcliffy]

Thank you for your report on this matter-
but, I must say that I am not sure why your experience would shake your faith in the NNNBC system...
my interpretation of your report is that some old equipment failed you on a backcountry tour-
I have had much old worn out equipment fail me-
including worn out equipment that I have tenderly and lovingly tended to and obsessively maintained.
I too have little faith in worn out equipment...
...........
NNNBC has been around for a long time-
and it is important to recognize that Rottefella has been tweaking the design of the bindings and the outsoles for decades- in a process of continous improvement in performance and durability.
Not only is old NNNBC equipment old and possibly worn out- it was not as good as the current designs in the first place.
.........
I must say that in my very limited personal experience-over a few decades- I have had way more failure of 3pin boots than NNNBC-
this is one of a number of reasons why I would not use a 3pin binding without a cable for any serious wilderness touring...

[lilcliffy]

Until very recently, I’ve used Araldite Standard (slow-curing, 2-component epoxy) to mount the bindings. Doing so is a bit of a two-edged sword – on one hand I have never (ever) had a binding rip out of the ski, but on the other hand it more or less rules out a field repair/replacement. To get the damaged binding and its partner off the skis I had to place a soldering iron with a chisel tip in the slot of the screw head and hold it there for 60 seconds at 380°C before the seal broke.

Curious- for a wood-cored ski- why use epoxy versus a polyurethane glue? Polyurethane glue will completely seal the screw and hole- preventing any moisture from entering the core- one can unscrew the binding by hand- and I have never had a binding pull using it.

Also- consdering the numerous screws on an NNNBC binding- I am curious as to your anxiety re a bnding pulling out on tour. Has this happened to you?

Mention was also made of snow packed in the toebar area. This has been given by Alfa as a reason for the toebar pulling out of their boots. Before stepping into the bindings I have always been fastidious about clearing snow from the toebar recess and the longitudinal grooves in the sole. I use the narrow Swix scraper for this, as the “T” end of the scraper fits perfectly into the recess. Packed snow in the recess and grooves of the boot is likely to put more stress on the toebar and the binding.

9 times out of 10 I find a few scrape-stomps of the boot against the binding rails will clear out any packed snow- YMMV

I believe there could be an interesting new development in the NNN BC format next season.

Ooooh...please do tell- what is this?

[Jurassien]

@lilcliffy Some questions and answers/comments on your above two posts:

I have had much old worn out equipment fail me-
including worn out equipment that I have tenderly and lovingly tended to and obsessively maintained.
I too have little faith in worn out equipment...

How do you decide when equipment is worn out? What are the inspection/test criteria? Distance covered or simply years since the date of manufacture? The NNN BC binding has been used for distances far in excess of my failed binding (Antarctic, Greenland, Norge på langs, etc.). and the ski-set in question is only one of a number of sets which I would use (or not use at all) in the course of a winter season – so it’s not as if I had used this set exclusively for the last 15 years (I have a lot of skis).

I’ll make the point again that it’s not the breakage in itself that bothers me as much as the lack of options when this system does fail. The “faith” comes from 30 years of almost trouble-free usage, the “somewhat shaken” from the (albeit belated) realisation that if and when it fails there’s not much you can do about it, and you could find yourself in serious trouble in a wilderness area. I’ve had enough snow bivouacs, both in practice and in genuine emergency, to know that it’s something I would prefer to avoid if at all possible, even though I carry the necessary equipment with me on tour.

NNNBC has been around for a long time-
and it is important to recognize that Rottefella has been tweaking the design of the bindings and the outsoles for decades- in a process of continous improvement in performance and durability.
Not only is old NNNBC equipment old and possibly worn out- it was not as good as the current designs in the first place.

Which improvements have been made to the NNN BC bindings and soles and where would this information be accessible? I’m aware of the difference between the Gen 1 and Gen 2 bindings (depicted), but the “Gen 3” bindings seem to differ from the previous incarnation only in their cosmetic appearance and not in substance. If I’m wrong on this I would be interested in seeing some relevant documentation as to why Gen 2 “was not as good as current designs in the first place”. As for the boot-soles: I have 4 pairs of NNN BC boots here from current to very old (kept as spares/loaners) and I can’t make out any difference in the sole construction.

......I have had way more failure of 3pin boots than NNNBC-
this is one of a number of reasons why I would not use a 3pin binding without a cable for any serious wilderness touring...

At the present time, this is also my view.

Curious- for a wood-cored ski- why use epoxy versus a polyurethane glue? Polyurethane glue will completely seal the screw and hole- preventing any moisture from entering the core- one can unscrew the binding by hand- and I have never had a binding pull using it.

Because it works! The epoxy does what I expect it to do, namely prevent the binding from parting company with the ski. The recommendation to use polyurethane glue is fairly recent. Previously, any outdoor wood glue was standard. I’m not aware of the moisture-sealing properties of epoxy being inferior to any category 4 wood glue, whether polyurethane or not.

Also- consdering the numerous screws on an NNNBC binding- I am curious as to your anxiety re a bnding pulling out on tour. Has this happened to you?

“the numerous screws on the NNN BC binding” – it has 3 screws in the stress area, the same as the NN 75mm binding, and the question about whether I ever had a binding rip out was answered in the passage which you quoted.

I believe there could be an interesting new development in the NNN BC format next season.

Ooooh...please do tell- what is this?

Ahh, now that would be telling, wouldn’t it?

“The path to enlightenment is a long and arduous one”

…………..so keep watching this space!

[Manney]

How do you decide when equipment is worn out? What are the inspection/test criteria?

Visual inspection. Looking for corrosion, *any* sign of pitting of metal.

Corrosion fatigue is common. The fissures often run deeper than they appear. So if corrosion pitting can be seen by the naked eye, deeper fissures are likely (that’s your criteria for critical parts). Stress cycling will eventually lead to failure… exactly where one would expect it.

The unblemished part:

The dome pressed into the metal serves as a stiffening element and a detent for adding some feel to the binding closure mechanism. It’s likely where the stress is the highest. Not much of a surprise that fatigue would occur where corrosion occurs and the stress is highest.

We get a sense of how this all works looking at the underside of the binding…

This was years in the making. Good of you to post the photos though… really helps understand what to look for, and where.

Guessing that a periodic shot of a film based lubricant (not WD40) under the plastic tab in the center of the photo will reduce the incidence of failure by displacing moisture and reducing friction.

[Jurassien]

I’ve had some constructive comments on this, both in the thread and by PM.
On the original photo the claw looked as if it had extensive rust, but what looked like rust was mostly dirt, and light brushing with a bit of solvent revealed bright metal. I couldn’t find any traces of corrosion at the break line, even on peering through a magnifier.

However, the metal certainly did have problematic rust and this was on the crown/outside bend of the claw, as can be seen by the visible rust patches and the blistering of the powder coating. This would have been at least partly visible when I prepped the skis in December, but I failed to spot it. If the part hadn’t broken where it did, this spot would have been a likely contender.

A top view of the intact claw shows two patches of wear (and two tiny traces of pitting) in the exact place where the other one broke.

......and the other side:

Some proffered suggestions/comments:
Carry a spare binding: A spare BC binding with its 5 screws and without the buffer and leash plate weighs 225g – a fair chunk to have to carry in a multi-day touring rucksack. The screws would have to be removed and kept separately for transport in the rucksack, and a Pozidriv #3 would have to be carried.

Use polyurethane glue instead of epoxy: I’ve started doing this, in fact I used it on my last two mounts, although I still don’t trust it as much as epoxy. It would certainly make a field repair easier.

Change out the binding after a maximum of 10 years – even if only lightly used: I think that’s the best advice and I’ll make that my cardinal rule in future.

Clear snow out of the toebar recess and the grooves before stepping into the binding: YES!! I already do this and advise others to do so.

Lubricant: I’m still a bit uncertain about which is best to use. Prior to using standard WD-40 I had occasional icing of the bindings (couldn’t get out), but since I started using it I have never had such problems – so it must have been having some effect. I wouldn’t use the lithium grease again, at least not with a deep-freezing propellant. Shock deep freezing of metal has been used to defeat hardened steel bicycle locks and I can’t help suspecting that it could have altered the molecules of the metal and caused or hastened the break. There must be a difference between metal adjusting to very low ambient temperatures as opposed to being subjected to sudden dynamic deep freezing.

Having said all that, for tours in remote areas I’ll be using the 3-Pin/cable for the foreseeable future.

[Manney]

Great photos, write up.

The area between the yellow lines deserves a very close look. Is that discolored metal?

There’s also an interesting cleavage at the green arrow. Hard to tell whether this was the start or end of the failure.

One thing’s for certain though, there was a clean fracture along the metal on the left of the photo. It almost appears that the metal in that area was grainy in structure.

Annealing is the process of cooling a metal after it has been heated to very high temperatures. When done properly (very slowly), carbon steel can be strengthened considerably by annealing. Annealing in this metal helps distribute the carbon while reducing internal stresses. We’re talking about cooling from many hundreds of degrees, starting from the point where the metal has some plasticity. The result is an even grain or lattice structure.

Annealing helps make carbon steel strong but somewhat elastic. This is a good thing in parts subjected to stress cycles… like a binding that firmly closes against a plate to locate a toe bar.

Quenching is different. It involves rapidly cooling the metal, from a near plastic state (glowing) to ~room temperature. This makes carbon steel very hard because it changes the internal structure of a metal from one of a grain to that of a large crystal. The problem becomes embrittlement, the signs of which doesn’t appear in your photos because the cleavage would be different.

Quenching for hardness is useful for things like knives or lawn mower blades which need to keep an edge.

None of this has anything to do with rapidly taking a part from room temperature to -40 with a spray Lube. Carbon steel would not be affected by this minor temperature swing unless it was under some kind of considerable internal stress. This doesn’t appear to be the case because the left side of the fracture indicates properly annealing, which would eliminate internal stress.

All the signs point to a corrosion failure on the right hand side, increasing work stress on the lefthand side until the part snapped clean through. Hard to tell from one angle precisely where it started… could be from the green arrow to the yellow area or vice versa.

Looking at the topside photo helps narrow things down…

99% sure this is the point of failure.

[Jurassien]

The area between the yellow lines deserves a very close look. Is that discolored metal?
[/quote]

Yes, there is indeed a difference in colouration. The brown shade is superficial surface oxidation since I did the clean-up, but the dark grey was definitely there before:

There’s also an interesting cleavage at the green arrow. Hard to tell whether this was the start or end of the failure.

The cleft can be seen better on the other side, and it appears to continue as a hairline crack along the edge of the embossment towards the notch between the claws:

[spopepro]

I’ll make the point again that it’s not the breakage in itself that bothers me as much as the lack of options when this system does fail. The “faith” comes from 30 years of almost trouble-free usage, the “somewhat shaken” from the (albeit belated) realisation that if and when it fails there’s not much you can do about it, and you could find yourself in serious trouble in a wilderness area. I’ve had enough snow bivouacs, both in practice and in genuine emergency, to know that it’s something I would prefer to avoid if at all possible, even though I carry the necessary equipment with me on tour.

I've been thinking about this while on runs, and I wonder if there's a place for an "NNN BC Expedition" binding. Manual, build the claw part (the one that failed here) out of titanium, and add a slot just behind it under the binding that would fit a voile ski strap. I bet one could even do these kinds of mods themselves as I'm pretty sure rotte is not going to be interested in innovating on something I suspect they consider "old tech". Maybe I'll see if I can make one.

[Manney]

Thanks for the last series of photos, @Jurassien. Seals the deal… definitely the point of failure.

The interesting thing about paint… it’s great for something called a vapor phase inhibitor. What that means is that it stops condensation from reaching metal. The downside is that if damaged, corrosion can happen under the paint without it being noticed… so often the corrosion is worse.

@spopepro WRT titanium… it’s a very hard, strong, light, metal. Many alloys resistant to corrosion. Truly a wonder metal. Brittle as hell though… can fracture (happens in turbine blades all the time). Notch sensitive too. Deep scratches can affect strength. Titanium may not respond well in applications where high clamping force occurs because it doesn’t flex much. That part is fairly large too… so the cost of a titanium replacement would be many times more than steel. Would drive the binding cost up considerably.

Always a cost/performance issue in any engineered product. Other approaches may be better… different steel alloy… don’t paint the part… or plate it… redesign the friction point away from where the stress is highest etc.

Edit: *alloys” not “allows”… spell checker has a mind of its own.

[Manney]

Btw, this has been such a cool exchange. Kudos to @Jurassien for sharing. Will definitely help others to know where to inspect, clean, and lubricate NNN BC bindings for maximum service life.