Bindings 101: How to mount Telemark bindings (Part II)
Black Diamond skis recommandation since 2015
This is paramount for telemark bindings, which have much higher peak loads than an alpine or AT binding. What is often overlooked is that the ISO standard minimum for binding pull-out strength for alpine skis is 292 pounds per screw, whichis fine for alpine binding systems but is not nearly enough for an active tele binding. Our pullout strength exceeds 440 pounds per screw, but that pullout strength is only achieved with a precision mount. For example, that strength drops 40% if the screw doesn’t thread in straight. How many times have you chased a screw hole that wasn’t completely in line with the binding and you just kind of forced it in, cocked over, until it snugged down straight? That's a major no-no.
Most alpine specs have around 4-5 Nm per screw when you are using a TLD (torque limiting device). For an active tele binding you need upwards of 8-10 Nm. Some company’s skis may not take this much, but for BD skis, feel free to crank it down this much (in fact you must on bindings such as the O1.) In addition, we recommend a 3.6 Ø drill bit to get the bestthread retention based on the minor diameter of the screw. This tighter screw fit also mandates a higher torque to get the screw into the ski, so again, the traditional TLD setting probably would not seat the screw tightly enough.
With tele there’s a bit of witchcraft at every corner. All bindings are not the same and in fact have drastically different forces associated with each. The boot size and skiing style greatly influence the degree of mounting sloppiness that can be tolerated. In addition, the screws, screw heads and shapes are different, and the industry lacks any sort of standard or unification, resulting in very specific mounting issues. For example: The tapered-head screws provided with K2’s older inserts work fine with BD bindings except for the O3, which requires a flat-head screw that interfaces with the plastic.
It’s important that you accurately determine your mounting location based on the recommended specifications with personal preference adjustments, if applicable or known. Measure twice, drill once. Again, things get complicated with tele. If you base all things off of the chord-center (or some reference point along those lines), different boot sole lengths will affect the mounting position and its relationship to the sidecut and overall length. The middle 26-27.5 is the baseline, shift 5 mm forward for 28.0 and up, and 5 mm backward for 25.5 and smaller. This keeps a good relationship between balance point of the ski and, most importantly, mid-boot in relation to the center of the sidecut.
Be sure to remove any dust or shards from the drilled hole. It is important to use clean screws, without any chunks of material embedded from a previous mount. A screw with smooth threads ensures proper thread cutting when you turn the screw in. It is also important to apply adequate downward pressure when starting the screw so the threads cut immediately and don't spin and grind away the first engagement. Tapping the hole first is never a bad practice regardless of metal or not. When mounting thinner skis that require the screws to be ground down shorter, be extra careful to grind a slight taper and to avoid leaving any sharp burrs which will not cut a smooth thread into the ski.
We recommend using epoxy for all telemark mounts. Epoxy can increase your overall maximum pullout strength, but most importantly acts as a buffer to decrease screw-loosening possibilities. This in turn can lead to a degradation of the ski’s core and increase peak shock loads that will eventually result in the binding ripping out of the ski. For alpine and alpine touring bindings, if you don’t prefer epoxy, use simple wood glue to seal the hole and lubricate the screw as it is being twisted in to help achieve suitable clamping force for given torque values.
Jigs are a great tool for precision tele mounts and keeping the heel block in the prescribed location every time or if you don’t have the actual boot to work with. (Sorry if you normally mount skis with the tips facing left. Perhaps you can stand on your head or mount behind your back, Jimi style.) Fully support the ski so that when applying drilling force you don’t flex the ski; this is crucial because it ensures that the holes are perpendicular. Some skis can get quite thin, so make sure your drill bit and provided screws are not going to dimple the base, especially at the heel block areas. We highly discourage any type of paper template mount as you will never achieve full strength and can also compromise the overall strength of your binding.
HOLES AND SCREWS
Each ski manufacturer has a recommended hole diameter and each binding screw design should have a specific hole diameter recommendation. Confused about which to use? Put down the drill and contact the manufacturer. If all else fails, use the binding recommendation and tap the hole. As a rule of thumb, the more expected force on the system, the higher torque the screws are going to need to resist the resulting binding force acting against it. When that relationship is out of whack, the screws can begin to loosen and even a single loose thread will dramatically affect pullout strength. It can also slowly degrade core-retaining properties by slight movements of the screw over time, again reducing pullout strength. Using torque limiting power drills is usually a bad idea unless you’re skilled in the art. We recommend hand tightening each screw with a TLD-enabled hand posi-driver, making sure that each screw goes directly and perpendicularly in and then doing a final torque spec twist on each screw. If for some reason you don’t have a TLD, hand tighten more than you think—pushing down with all your strength while turning the screw means that you’re probably at around 10 Nm.
RECAP OF THINGS NOT TO DO:
- - Don’t re-use old screws that have crap plugged in the threads. When you screw that into a new ski you
are cutting crappy threads into the core and compromising strength.
- If you need to grind screws for some reason (e.g., the ski is thinner than the screw design provided), be
extremely careful not to leave any burrs—these will mess with the thread cutting of the ski core.
- If you get a spinner and strip a hole, don’t half-ass it—fix it right by putting a heli-coil in.
- Don’t reverse bend the ski when applying drilling pressure. Support it from beneath so that the screw hole is perpendicular to the ski. Even a small amount of flex will change the angle and you'll lose full pullout strength potential.
- Don't grind out your initial hole threads by carelessly spinning the screw without downward applied force.