Binding reinforcement testing?

vinman · Post by **vinman** » Sat Dec 10, 2011 5:29 am

Has anyone (commercially/ home builders) actually tested, in some measurable way the various binding re-inforcement ideas floating around out there?

I know PM gear uses their dore-tec and some guys use some extra glass but to me this all seems relatively worthless. I mean you are just drilling a hole though whatever layers you put down and how much can the threads on the screw really grab onto a section of window screen or even extra glass for that matter.

To me adding extra glass under the screws just means there are less screw threads in the wood. I can see a layer of titanal or even some kind of UMHWPE mounting plate being useful but other than that I'm skeptical.

Ideas? Am I nuts? Does Dore-tech or some other fabric really have any real effect on pullout strength?

Idris · Post by **Idris** » Sat Dec 10, 2011 10:06 am

dore-tech was metal screen door material - and on the original prototypes, compared to the ski without any reinforcement - all built my local snowboard company it was night and day

The ski without reinforcement I could rip the binding out of the ski by wrenching on a ski boot in the binding.

The one with the reinforcement I smashed the binding apart before the screws failed.

All this said if I epoxy the screws into almost any ski when I mount the bindings there has to be a major breakage of the ski for the binding to pull out.

Beware of putting any painted screen door material on your ski - you will create another fail point.

SHIF · Post by **SHIF** » Sat Dec 10, 2011 11:00 am

I think such a test could yield some useful information.

twizzstyle · Post by **twizzstyle** » Sat Dec 10, 2011 12:49 pm

When I worked at K2 I did a lot of testing for binding retention. They put an extra layer of fiberglass in, and it does make a difference.

There were two ways I'd measure it, one is just to pull vertically until it rips out, the other is to tighten the screw until it strips and measure the torque. Either way, the extra layer of fiberglass makes a big improvement.

vinman · Post by **vinman** » Sat Dec 10, 2011 3:07 pm

Ok that is some good evidence for reinforcement.

Idris, I know those early PMG cores were either fir or aspen. Do you think this softer wood had anything to do with the tear outs you saw?

Same question for Twiz, what kind of core material was being used?

We all debate on wood choice for cores and I wonder if there is any difference between say screwing into maple vs poplar vs fir vs aspen etc...

Without testing I would say yes those softer wooods would be more prone to tear out vs screwing into maple or ash. But I guess the question is what is the threshold? How much force does a skier create on an individual screw? And what types of wood meet or exceed this requirement without reinforcement and which ones should get reinforced?

Maybe I'm over thinking things a bit but it was something I was thinking about adding to my lay up especially for bigger/ heavier skiers.

MontuckyMadman · Post by **MontuckyMadman** » Sat Dec 10, 2011 3:12 pm

you can feel the extra grip when you screw into it. I use a 17oz biax with a matt/chopped backer.
I did the al screen but it was kinda a pita for layup.
Praxis advertises a perforated rubber for binder retention. No idea what he uses. He also uses a rubberized epoxy. His skis in the 188cm range weigh 10lbs for the pair.
I have a few pair that are just poplar and no mount plate and you can feel the difference when mounting.
Virtually every layup video you see they use an extra composite in this area.

vinman · Post by **vinman** » Sat Dec 10, 2011 3:29 pm

http://docs.google.com/viewer?a=v&q=cac ... FLUuCJXZ-g

Nice article with some mounting tips. Also quotes the ISO specs for individual screw pull out force. Min force per screw should be 4-5 Nm or about 292lbs per screw.

Maybe a torque wrench is on my tools to buy list.

skibum · Post by **skibum** » Sat Dec 10, 2011 11:16 pm

Twiz what type of fibreglass were you guys using back then? A matt of something like MM is using (biax with matt backer).
I currently use just a matt but just want to make sure it is as strong as possible.
Idris thanks for the tip on epoxy, I didn't realize it made such a difference. I guess that is why dynafit's require it.

Richuk · Post by **Richuk** » Sun Dec 11, 2011 4:18 am

Vinman, you might have seen these links already:

http://www.woodweb.com/Resources/wood_e ... k/Ch07.pdf @ 7 - 11, so the density of the wood used in the binding area of the ski is important.

A second layer of fibre (triax) is OK - it tends to increase individual binding retention by about 25 - 35 Kgf.

ISO standards are agreed international testing method and minimum results. This thread should put Black Diamond into context:

http://www.telemarktalk.com/phpBB/viewt ... sc&start=0 - there's a comment at the end of thread which talks about the effect of the topsheet. Pinch your forearm and gentle pull, you'll see the effect they're talking about. So choice of topsheet is not just about scratch and charpy results - perhaps?

My own results gave a peak value was 401 Kgf, so that's 884 lbs. According to the lab it was a big bang when the it final gave out - no aluminium involved in this result. This is so over the top its not realistic - I'd expect half a leg to still be attached. At the end of the season, I hope to test and see what the values are after a seasons use.

Hope the above links are helpful!

twizzstyle · Post by **twizzstyle** » Sun Dec 11, 2011 8:39 am

skibum wrote:Twiz what type of fibreglass were you guys using back then? A matt of something like MM is using (biax with matt backer).
I currently use just a matt but just want to make sure it is as strong as possible.
Idris thanks for the tip on epoxy, I didn't realize it made such a difference. I guess that is why dynafit's require it.

I wish I could remember but I can't. I think it was just a mat, pretty heavy too. Of course with k2 they don't use just layers of triax, they have their insane braiding machine that wraps the whole core. One of the coolest pieces of machinery I've ever seen! I *think* they put the mat on the core, and then wrapped it with the braiding machine... But again I am going off fuzzy memory, so don't quote me. If you look at a clear top k2 ski (like the old pep fujas) you can see the binding layer.

vinman · Post by **vinman** » Sun Dec 11, 2011 12:47 pm

based on some of that info I would suspect that as long as we are screwing into decent hard wood at a 90 deg angle and using the right size bit we are generally ok.

This seems to differ with alpine and tele gear though. This info makes a good case for epoxy as well.

I guess I'm still not clear on what type of re-inforcement is best to use. I might look into some stuff like MM uses.

MontuckyMadman · Post by **MontuckyMadman** » Sun Dec 11, 2011 7:07 pm

I heard BD routs an area in there core where they drop some plastic in for binding reinforcement.

vinman · Post by **vinman** » Sun Dec 11, 2011 9:27 pm

Like tip spacer material maybe? I guess as long as it doesn't delam...Thays a lot of tension and pulling on that kind of interface.

barnboy · Post by **barnboy** » Wed Dec 14, 2011 3:54 pm

Anyone who has ever worked in a rental/repair shop (good idea if you can handle watching other people ski...) can tell you the standard for screw torque when mounting an alpine set-up is 4nm. Most of your electric screw guns with torque clutches use some oddball proprietary numerical system that doesn't seem to correlate to anything... a torque limiting screwdriver can be used to set your gun to whatever number you're actually trying to hit.

For tele-heads, BD has long recommended going well beyond the alpine 4nm standard, this year their literature suggests 10nm, with epoxy in the screw holes, and an overnight cure. From what I've seen so far, their cores are still wood in the mounting area on both lines of skis.

I've definitely seen a TON of alpine bindings come off, across all brands , makes, and models, and from multiple shops. Usually, core rot is the culprit.

gladegp · Post by **gladegp** » Tue Jan 10, 2012 3:27 am

I don't have a lot of experience with skimaking but I have had problems on my first skis with the bindings ripping out.

The first skis I made were made out of fir and I'll never use it again. I mounted the bindings myself with epoxy and had no problems although I think I remember that already at the stage of tightening the bolts I had questions about the choice of wood.
I mounted the skis with dukes and skied them for a couple of days before the binding came off, which also led to my Dukes snapping in the baseplate

I then had the bindings remounted a couple of cms back with some type of inserts inserted from above. This was done by a store in Austria. This lasted for another couple of days before I ripped that binder. Looking for a heelpiece of a binder in 30cm of pow is not so much fun after the first 30min

=Fir is no good

Poplar felt similar

I've also done skis in oak and that wood is SOLID

but very heavy. It had a completely different feeling to it when I tightened the screws. I could tighten until the screws stopped without beeing worried about overtightening.

I think I'll use ash or potentially bamboo in future skis, with an extra layer of fiber under the binding and epoxy in the screwholes.

I have a few poplar cores at home and have been thinking about cutting out 5 mm under the binding and replacing it with 5 mm of ash. I'll get back to you if I'll actually follow up on this thought.

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Binding reinforcement testing?

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Fir is no good