NNN BC - faith somewhat shaken

[Jurassien]

Will definitely help others to know where to inspect, clean, and lubricate NNN BC bindings for maximum service life.

Unfortunately, it doesn't say much about how to avoid a comparable unpleasant surprise with the boots – other than to further burden our already struggling environment by discarding after a few seasons. Another reason, perhaps, for continuing to give life-support to the NN 75mm.

By the way, is the red coating on the claw metal a powder coating or just paint, and how does one tell the difference?

[Manney]

Toe bars aren’t subjected to much stress… they’re allowed to rotate and are merely kept in place by the binding. The plastic retainer integrated into the sole of the boots can be damaged by walking over hard surfaces. Pins can be bent that way too. Takes a lot or carelessness though.

Easy to prevent… don’t use them as hiking boots, clean and inspect regularly. NN boots can crack from normal use too… that’s why smiley plates exist. Even a welted boot can split… expensive to fix outside of Europe where the practice of shoe and boot making is pretty much lost. Always wise to have spares.

Idk if the coating on the claw is paint or powder coat. Hard to distinguish between powder coat and paint after a long period of use… they can both flake and peal if the underlying metal rusts. Easy to tell when new though… paint is usually smoother, thinner, can have a deeper shine.

[Jurassien]

I'm pretty sure rotte is not going to be interested in innovating on something I suspect they consider "old tech".

It is “old tech”, but the NN 75mm is quite a bit older and they’ve recently improved that by (finally) adding an effective cable assembly.

I believe something might be in the offing in House Rottefella with regard to the NNN BC norm. If so, we’ll know about it this coming season, and if it doesn’t materialise by next season then it’s unlikely to happen. I’m not an industry insider, but my suspicion is based on the following:

The Norwegian military is currently in the process of deciding on new skiing equipment. The Defence Ministry published the Invitation to Tender (ITT) on 5.Oct 2022, with a deadline of 3.Nov.2022 for manufacturers to submit their proposed equipment. The plan was for the military to evaluate the submitted equipment this past winter season and for contracts with suppliers to be entered into during the second and third quarters of 2023. I have seen the ITT and it is interesting to note that a BC binding is included in the requirements (in addition to a military boot-compatible binding), which raises the possibility of a modification to the NNN BC format to reflect military usage. A beefed-up, military-grade BC binding is, of course, pure speculation on my part, but it does seem to be a not unreasonable expectation.

Plastics are already widely used in firearms manufacture, albeit very robust plastics. Why couldn’t the existing plastics in the BC format be replaced with similar robust plastics without altering the geometry of the binding? How about a tougher grade of steel for the metal parts – again without changing the geometry?

In any case, I’ll hold back on mounting spare BC bindings of the same vintage as the broken one (held in reserve for many years) to see if a beefed-up version appears next season. Rottefella already markets three versions of this binding in parallel, so why not a fourth?

For those who might be interested, here is a translation of the relevant brief description from Section II, Paragraph 1.5 of the ITT:


II.1.5) Short description

This procurement will equip the Norwegian Armed Forces with a flexible system for fast, agile, autonomous non-mechanized mobility on snow. The general requirement is for: -
Robust skis with steel edges, designed for long trips through forest, moorland and mountain terrain. –
Robust skis without steel edges, intended for long trips through forest, moorland and mountain terrain. –
Climbing skins –
Robust ski boots, with removable liners, made for long trips through forest, moorland and mountain terrain, in temperatures between -40 degrees and +10 degrees Celsius –
A binding that can be used with field boots (my remark: standard-issue military boots) –
A BC binding –
Telescopic ski-poles

[riel]

which raises the possibility of a modification to the NNN BC format to reflect military usage. A beefed-up, military-grade BC binding is, of course, pure speculation on my part, but it does seem to be a not unreasonable expectation.

Plastics are already widely used in firearms manufacture, albeit very robust plastics. Why couldn’t the existing plastics in the BC format be replaced with similar robust plastics without altering the geometry of the binding? How about a tougher grade of steel for the metal parts – again without changing the geometry?

I suspect the plastic and steel used in BC bindings is already more than strong enough. After all, ripping out a binding is a lot less dangerous than ripping the sole off somebody's boot. Carrying a few spare bindings in a squad is easy, while carrying spare boots would be a nightmare.

The most useful change to the BC binding I could see would be some small geometry changes to reduce snow and ice buildup underfoot. Maybe change the flat part between the ridges to be convex, and have some gaps in the ridges. That way stepping down would push snow and ice out of the ridges, instead of getting it lodged in the ridges.

However, it is also possible the Norwegian military simply ends up with XPlore bindings and boots, if those end up being more reliable for their use case.

[tkarhu]

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.

I do expect that a binding will fail at some point. If and when I go on a one-week expedition, more than one day skiing away from roads, I will carry a spare binding. And yes, I have bought a short Pozi #3 for that use. There I will have a Paris pulk, and 225 g is not much. For a weekend tour with a backpack, I have carried the Pozi #3 and even a set of spare screws, but not a binding.

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.

In Finland, old school wood glue (dispersion glue) is used for bindings. Of course one that is meant for outdoor use. If I remember correctly, that is also Åsnes' instruction. A service guy at my local BC ski shop, whom I trust, would probably kill me for putting epoxy to my bindings.

I do not trust polyurethane much because it degrades after a few years. For example, I avoid polurethane based shoe soles for this reason. I think if you do not put pressure or usage on polyurethane, it will fall to pieces after a certain period of time. On a pair of shoes, leather was still nice and well treated, but soles fell apart, in two pieces.

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.

This makes a lot of sense to me. But sounds like a good reason to use glue that does not rip your drill holes. Maybe polyurethane is great there, too.

EDIT: Looks like s Cascol wood glue is actually polyurerhane glue. Yet some others are PVAC that ski shops use here.

[Manney]

There are a lot of misconceptions around how adhesives work in bindings. The most popular misconception is that the adhesive “holds” the fastener into the ski. This is only the case if the hole is improperly drilled. If the hole is properly drilled, the interaction between the threaded fastener and material into which it is fastened does all the work.

At most, adhesives used in bindings act as a thread locker… they prevent the screw from backing out. Glue does not prevent tear-out. Responsibility for that lies solely with the material into which a fastener is threaded… the ski.

The advantages of polyurethane glue are that it is thin, flows well, flexible, has a low expansion pressure, and is impervious to water when dry. When it expands in a hole drilled into a ski, the excess goes into the air channels in the base and doesn’t damage surrounding fibres. Seals everything up. Creates a “web” of adhesive… beyond the threads.

Cured and expanded polyurethane adhesive will crumble to dust if left in the sun, no different than a urethane finish on a wooden door to boat deck exposed to the elements. It can also crystallize if applied and *cured* at cold temperatures. This happens with expanding foam window insulation if it is applied in the winter. None of these things are happen when polyurethane glue is applied and left to cure at room temperature remains shielded from the sun.

There was a time that hot glue or even wood glue was used for bindings. Those were the best products of their day and were used when skis were made from solid hardwood. Then hardwood laminates came along. Those are mostly gone, replaced by softer birch, poplar, pawlonia and synthetic laminates.

So times and materials of changed. Not surprising that the recommended adhesives used in these newer materials changed with them.

[Stephen]

There are a lot of misconceptions around how adhesives work in bindings. The most popular misconception is that the adhesive “holds” the fastener into the ski. This is only the case if the hole is improperly drilled. If the hole is properly drilled, the interaction between the threaded fastener and material into which it is fastened does all almost all the work.

At most, adhesives used in bindings act as a thread locker… they prevent the screw from backing out. Glue does not prevent tear-out. Responsibility for that lies solely with the material into which a fastener is threaded… the ski.

It seems to me that, for the most part, the discussion of what adhesive to use is somewhat theoretical. Most of the time people do whatever they do and it works out fine for as long as it needs to.
But, on a scientific basis, I believe there are differences in the pullout strength of different adhesives.
(But, those differences may not matter, as long as the primary need to keep moisture out of the ski is met. In most cases, the holding power of the screw, alone, is enough to keep the binding attached to the ski.)

For me, I think possibly the only time epoxy is beneficial is when mounting bindings to skis with low density cores, such as paulownia. If the epoxy is allowed to soak into the soft paulownia wood core, it creates a higher strength plug around the screw that will increase pullout strength.
https://www.westsystem.com/instruction/ ... -hardware/

I like using epoxy because I’m familiar with it, I have it, and because it has a VERY long shelf life, unlike polyurethane glue, which seems to last a year or two before becoming unusable.
I think the downside of epoxy (difficulty in removing fasteners without damaging the ski) speaks to its increased holding power. And, if the fastener is gently heated, the epoxy is softened enough to remove the screw without damaging the ski.

[Manney]

This is not theoretical. But before we get to that… my post said “threaded fastener and material into which it is fastened does all the work.” It didn’t say almost all. Reasons for that at the end of this post.

Epoxies are higher density mixtures of a base material (usually plastics or metal matrices) and volatile organic compounds, some of which keeps the base material soft until activated by a hardener. Polyurethane glues are chains of monomers (polymers) based on urethane molecules that harden in the presence of air and moisture.

When the VOCs boil off (and they do so at room temperature which is why they have a strong smell) what happens to the volume of the epoxy? It shrinks. Maybe not by much… but it still shrinks. Polyurethane adhesives are the opposite… they are activated by moisture and expand to seal small voids around threads (they’re not “fillers” and do a poor job of filling large voids).

What do you think VOCs do to plastic caps, rubber damping layers within something like a ski? Remember… they’re solvents specifically designed to soften synthetic materials. That’s how they work.

All these issues are practical, not theoretical. There are good reasons why *ski* manufacturers recommend things. Their desire is to avoid breakages, attempted returns, and unhappy customers. Competent ski techs use what’s recommended too.

Re: the web link… A marine adhesives web site discussing the use of epoxy for *repair* is talking about “fillers”. It is not the same as an adhesive, even though fillers can stick to wood. Nor is it the same as a thread sealer, even though some sealing might occur when using a filler. Also, a ski binding deals with unique cyclical stresses. Binding screws are tension fasteners, not shear fasteners.

If the original mounting holes are damaged to the point where they need to be drilled out with an oversized bit, epoxy may be the only practical thing to use to fill the gap between the hole and the shank of the fastener (ideally these should be the same diameter, leaving the threads to cut into the ski base but this isn’t possible with an oversized hole.). You’re still left with the unfortunate circumstance of using a fastener whose pitch was designed for maximum hold in wood being used to gain an hold into some sort of plastic epoxy.

The increased holding power you speak of is meaningless. The strength of the glue doesn’t impart magical qualities on the ski base material. It’s still the same wood (i.e. cellulose, which gives a clue into how it is structured) base. If the pullout force exceeds the strength of the wood, the binding or ski fails regardless of what glue was used to secure the fasteners.

[lilcliffy]

@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).

Good question- and the answer is- it depends- on a lot of things/contexts!
All I know is that I would not take a heavily-used kit on true multi-day wilderness excursion without the kit to completely repair/replace a binding...

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 think we would need Rottefella to speak to this explicitly. As far as the outsoles- at least from visual insepction NNNBC I,II&III outsoles are quite different. My very limited experience is that they have become more durable- but, perhaps this is not true. We (my clan) have certainly not had a NNBC outsole fail in a very long time...
Again- perhaps only Rottefella can indicate the actual differences...

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.

Well- I have never used epoxy on a ski binding mount (not unless a shop tech used it and I did not know)-
I have been mounting my own Nordic touring skis for decades- and have always used wood glues- no issues.

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,

I don't think that I agree with this...
There is definitely more than 3 screws supporting the NNNBC binding- especially when the binding is truly stressed with the ski fully-weighted, with the boot engaged in the rails...
I have seen many 3-pin bindings pull (over many decades)- I must admit that I have never seen a NNNBC binding pull out.
..........

Regardless- I do agree with you that a standard 3-pin NN Nordic touring binding is easier to rig up a survival mod than NNNBC (especially if the 3pin binding has a cable!)-

I still don't think that 3pin is inherently more reliable-durable than NNNBC.
I carry extra NNNBC bindings on a multi-day wilderness tour.

[Jurassien]

The subject of appropriate glues for binding montage has crept into the thread, and my statement that, until recently, I have almost always used epoxy led to some reaction and the drift into the adhesive debate.

The “received wisdom” is that the binding is held in the ski primarily by the engagement of the screw threads with the wood of the ski and that the main function of the glue is to prevent moisture from entering the ski core.

To those who would harbour any doubts as to the ability of epoxy to bond metal to wood may I suggest the following little experiment, which can be carried out in the comfort and privacy of your own home. Assuming access to a power drill, the material requirements are very modest:


Take a piece of scrap wood with a flat surface
Take a wood screw with a non-tapered shank, of the same shank diameter as a ski-binding screw (6mm), but somewhat longer (20 to 25mm overall length) and with a sharp tip
Some slow-curing, two-component epoxy
A pin, small nail, or paperclip
A drill-bit somewhat wider than the shank of the screw (I suggest 10mm)
Hammer
Screwdriver
Pliers

Drill the wood with the 10mm drill to a similar depth as a ski-binding bore-hole (9 to 10mm).
Mix a small amount of epoxy and fill the bore-hole. Have a small nail/pin/paperclip at hand to prick any bubbles which might come up – the aim is to get as much glue as possible into the hole. Use the head of a small nail or a matchstick to poke it in.
Set the screw centred in the hole and give it a tap with a hammer to seat it and/or give it a very slight turn with a screwdriver – just enough to have the screw standing upright in the middle of the hole.
You should now have something like this:

The screw is standing upright in the hole with minimal direct contact, apart from where the tip has been driven into the bottom of the bore-hole. There is no contact between the screw-threads and the side of the bore-hole.

Leave the glue to cure (usually 12 hours for slow-curing epoxy – I left this for 24 hours).
Now place the wood on the ground, put both your feet on it to hold it down, and try to remove the screw by grabbing the protruding head with the pliers and pulling directly upwards.
Let us know how you got on.

When you’ve had your fun at this and have used up your entire repertoire of swear-words, repeat the above steps, but using polyurethane glue. Use disposable gloves, as you want to avoid getting PU-glue on your skin. You can moisten the bore-hole slightly, as we’re told that PU-glue likes a bit of moisture to get it started. The PU-glue used here is the same brand and type as shown on the Åsnes website – so appropriate for ski binding montage.

When the glue has cured (again, I left it for 24 hours), take the pliers and pull upwards on the screw – this time without the bad language.

The two contestants square up to each other:

The result: KO in the first round – after about 3 seconds:

Both screws used were identical:

The above experiment says nothing about the moisture-sealing properties of the adhesives used. PU-glue has been attested to elsewhere as being very good at sealing out moisture. However, epoxy has been said to shrink over time and, by implication, have its holding and sealing properties diminished. Here is a photo of the 5 screws removed from the broken NNN BC binding. As stated in the opening post (penultimate paragraph), this binding was on the ski for 15 years and covered a very considerable mileage. On removal from the ski, after brushing off some wood/adhesive residue, I could find absolutely no trace of corrosion on the screws and would have no inhibitions about re-using them for another binding montage:

My conclusions:
1) A binding screw which has been epoxied into the ski will not come out, even when you want it to (unless you apply considerable heat, as described in my second post in this thread). The holding power remains undiminished, even after 15 years and considerable mileage.
2) The moisture-sealing properties of epoxy remain undiminished, even after 15 years and considerable mileage.

Epoxy for President!