Binding tightening torque

[rhaskins]

So, I have new bindings and boards, and I finally became inquisitive on how much torque to use to fasten/tighten my bindings to my boards. I did search the archives and found a massive amount of opinions about how much to tighten. Not really a consensus. My car has a recommended torque setting for the wheels (a sort-of analogy), why not bindings.

So, I emailed Sean Martin, manufacturer of every alpine board I have. He kindly gave me permission to publish this exchange.

Me: I have 3 Doneks: Axxess, FC1 and a Razor. Question: How much torque should I put on binding mounting? Inch/lbs, newton/meters, stone/furlong?

Any recommendations? I have searched around and can really find no consensus.

Sean: That's a question I've never had before. When mounting a freeride binding with a #3 phillips screw driver, I apply as much torque as I can gripping the screw driver with my bare hand. I'm not equiped to measure such a thing. Mounting bindings with an allen wrench is a bit different. We see things overtightened and under tightened at the SES. With the aluminim bindings, you'll get a sulfer odor when you crack the screw loose if it's over tightened. I'd say the torque is about the same as with the phillips screw driver, but since you're dealing with a different shaped tool, it's tough to know.

My suggestion to you would be to hand tighten things, so you can fairly easily remove the screws by hand. Check the hardware frequently to see if it's loosening up. If it is, then tighten a bit more next time. It's important to be able to remove the screws as hot waxing should always be done without the bindings mounted.

Me: Thanks for the quick reply. Do you mind if I publish this on bomber? I want to find out what others are doing. I am supposed to receive my Catek FR2’s today for my Razor, and am going to order some TD3’s for my FC1, so this is a question of interest for me.

Sean: You are welcome to publish it. Fin at Bomber probably has some exact numbers as he's more knowledgable about bindings and the ASTM standards surrounding them.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>

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<o:p>Anyone know of a good, all purpose spec for torque? Anyone have any other manufacturer recommendations? Is there a spec that the "good" snowboard shops use and keep as a trade secret? I use a phillips driver in a driver handle to tighten soft bindings just like Sean says, but not for my alpine stuff.</o:p>

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<o:p>What I am looking for is consistency. A "L" or "T" handled hex driver can have vastly different amounts of torque by the same person due to shape. A hex driver in a driver handle would be really different also. In manufacturing, we use torque drivers for consistency (and calibrate them). I am going to be removing my bindins for waxing from now on and I don't want to under or over tighten. And, yes, I can be kinda anal. I don't want to strip out an insert nor do I want to have my bindings come loose.</o:p>

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<o:p>Rick</o:p>

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[rhaskins]

The garbage in the post was from cut and paste from my email that I did not see before I posted it.

Sorry.

Rick

[BadBrad]

I've used Burton raceplates for over a dozen years, and I always tightened the phillips screws as tight as I could with a regular screwdriver. I also carried a small T-handle tool with me to the slopes and tighted that as tight as I could as well. Nothing has ever come loose, and I've never had any stripped threads or other damage from overtightening. I do check tightness every day or two of riding.

For the Bomber bindings with the allen head screws, I recommend getting the T-handle tool. It makes adjustments quicker and easier, and it is a good tool to feel for the proper torque. For me, I tighten the screws until they stop turning and when I feel the hex tool twist a bit, then I know they are tight but not too tight.

You used the car analogy. I do my own car mechanic work, and I have built racecars in my garage, and I am pretty anal about following the torque specs in the manual. But I have also gained a good feel for what the proper tightness is for various fasteners. For example, spark plugs are just moderately snugged down to prevent stripping or galling the threads (something around 12 ft-lbs or so). Same for brake bleeder screws. Lug nuts are tight, but not super tight (around 70 - 90 ft-lbs depending on the car, up to 150 ft-lbs on a truck or big SUV). But suspension adjustment bolts that get a lot of stress during racing on sticky tires need to be super tight (like 180 ft-lbs+). For snowboard bindings I would say very tight using a screwdriver handle or moderate force with a tool with more leverage like a T-handle. Don't use a ratchet handle because it's harder to feel when you have it tight enough.

[Corey]

I've often wondered this as well. I believe that we operate so far under the breaking stresses of the 4 bolts that it really doesn't matter from a bolt preload view. That makes sense as I've never seen a broken binding-to-board bolt. Other higher stress applications need to have the bolt preloaded to a certain extent to keep the bolt from fatiguing due to varying stresses.

The limiting factors are likely the insert itself and the core that the insert is in. They're likely to be damaged by undertightened fasteners, cross-threading, or foreign debris.

I found this: http://www.misumiusa.com/uploadedFiles/Technical/METRIC1847-1848.pdf

They suggest 138 kgf-cm (about 10 ft-lbs) for an grade 12.9 M6 bolt lubricated with oil in steel. They show a k value of 0.45 for a dry bolt in stainless steel. Running the numbers gives 365 kgf-cm or 26 ft-lbs! That seems really high!

My gut feel is that anything between "snug enough not to loosen" and "doesn't strip the insert" is just fine. Defining those upper and lower limits is tough... ;)

[BadBrad]

I agree that the inserts are probably the weak link. Some Madd boards have brass inserts, and I'd be especially careful with those.

[JoeK.inVt]

I have found base dimpling to be the most common problem I have faced when mounting my bindings. Different boards will handle the stress in different ways, so sometimes you just have to "feel it out" and find a happy medium.

[John E]

Why hot wax without bindings attached? Would it be OK to just loosen the screws?

I too just tighten the screws as tight as I can grip a #3 phillips driver.

[D.T.]

Let's look at this a little differently -

Scenario #1:

You install your bindings at home using your torque wrench, which in order to follow recognized standards, you have calibrated and certified on a yearly basis. Once you get to the hill a start riding, you realize that the stance width is too narrow. You get out the 5mm allen wrench that is provided with the bindings and attempt to loosen the screws. You quickly realize that there is no way in he!! that you can generate enough torque to break the fastener loose; now your are stuck either trying harder and potentially rounding-off the wrench or head, or your have to live with the incorrect stance width until you have access to your torque wrench.

Scenario #2:

As documented in other places, not all boards are made the same. As you install your new bindings, at home, using your certified torque wrench, you attempt to torque the screws to the value specified by the binding manufacturer. Before you reach that torque, you strip an insert. You are really pissed and call the board manufacturer, they tell you tough because you tightened the fastener to too high of torque value. You contact the binding manufacturer, they tell you tough because the inserts are not strong enough. You then vent your frustrations by logging into your BOL account and bashing both the board and binding manufacturers.

Scenarios 3 through ...:

Use your imagination

Scenario #138,924:

The manufacturer provides one wrench. Through their testing they know that when the average person tightens fasteners using the provided wrench, that adequate torque is generated 1) so that the fasteners do not loosen during use, 2) the applied torque does not exceed the shear strength of the insert threads, 3)...

[rhaskins]

I know what I am going to do: change from a Tee wrench to a nut driver with the correct bits, and just tighten them up fully with that. Limiting factor for tightness is the amount of torque that can be transmitted through the grip. That should get them tight enough without even approaching over-tightening. On slope I will carry my little DaKine Tee tool with the correct bits and lay off the alcohol so I don't over-tighten anything.

Having been involved with calibration labs and designing a few things, I know that manual tightening, even with calibrated torque wrenches, has a lot of variability. A torque wrench for binding tightening would be all wrong, but a torque screwdriver might not be bad at all. get to a 2.5 sigma that has an overall +/- 25% variability would be ok for such a manual process. If I remember right, a tightness of 30% of a fastener's tensile strength is a fairly common factor for the amount of torque to apply (all other things being equal like lube and etc.). That would be very over-tight for a binding screw. I would definately back off from that.

Let's face it: if there were widespread problems tightening bindings and blowing out board inserts, it would be widely reported. It is just not happening. My concern is with repeated over-tightening and loosening, and the effect that may have over time on the board. I plan on waxing my boards probably 15 or more times in the coming season (just because I can!), and I just want repeatable tightness without any issues on the slope or to the boards. Not too loose, not to tight, I want them just right.

I just wanted to see what others are doing and if there were more of a systematic way of doing this. It sounds like everyone applies their own windage to the issue.

Thanks for all your input.

Rick

[John E]

Seems like the biggest risk to the board inserts would be installing/removing screws repeatedly. At some point the threads will start to wear or worst case, you may cross-thread them.

Again, why remove the bindings to wax? If you wax with bindings removed, once you install them, you will get a low spot beneath each insert.

[Mike T]

Bindings such as F2's, Burtons, and soft bindings that mount with a Phillips or Pozi are danm near impossible to overtighten. This goes doubly so for The F2's which where the disk is very thin and mounts flush to the board.

TD's are VERY easy to overtighten IMHO if you use a T-wrench and apply all your might with your writing hand. I'm right handed. I tighten the TD disk-to-board bolts using a T wrench with a moderate grip using my left hand. I do the same with the plate-to-cant bolts, using my right hand.

That seems to get things tight enough such that I've never had anything loosen, but not so tight that I cannot tweak on hill if necessary.

When undoing bolts I use the same T-handle and place the board on snow or carpet so that I can fully decamber it. Board on tuning bench = stripped bolts.

[Corey]

On critical fasteners the bolts are usually preloaded 70-90% of their yield strength. In a properly-designed joint (i.e. one in which the bolt is never pulled so hard that it relaxes the clamping force of the joint) the most stress the bolt will ever see is during the final torquing.

I don't think it matters at all for a snowboard though as 4 M6 bolts are overkill... ;) Using four is nice for the rare occasion when one gets loose without us noticing.

I was surprised at how tight the guy in the cowboy hat at the Bomber SES demo tent (sorry, can't remember his name now) cranked the TD2 screws. We're talking 2 hands on a T-handle wrench and a good amount of effort. It was easily twice the torque I'd ever though of putting on mine.

[bigdyno]

I use a short allen key to tighten mine (about 4") by hand a leave it at that. I usually check at the beginning of the day and again at lunch, just because I'm like that. I usually have to go easy as I am too used to the bolting up I do at work, 6800-7000lbs, but then we use a hydraulic pump for those bolts. Don't do that.

[Justin]

Stretch the bolts with a jack at 16000 psi and tighten finger tight

[TVR]

Amazon now has bolts cheap enough to where I just replace them with 50 packs whenever they get buggered at all....

M6x1.0 and choose the length which is 10mm to board or 14mm / 16mm for TD bindings
m6x1.0 8mm head cap for Allflex replacement
M8x1.25 and 16mm for TD upper to lowers

 

No reason to go to the depot or Lowes....

 

The stainless is what I am talking about here...

[Deuxdiesel]

Use the German system- gudentite.