PSA: Mount your own fucking skis.

[Ted Striker]

Many in this thread do tap their holes. On a metal ski, it's a requirement. For a wood ski, it's preference. I personally do not not as I want as much material displaced and therefore engaged and the screw shank for maximum hold. (that's what she said)

Not that it really matters, but a I think a tapped hole usually has better resistance to pull-out / strength, whatever you want to call it. And epoxy definitely increases strength. Neither is really necessary though.

I don't have the link handy but I'll see if i can find it...


@ mkalynchuk
As Bob said the standard depth for alpine binders is 9.5 mm. The screws should protude approx 8.5 below the bottom of the binding. As for gorilla glue, I don't use it because it expands, but you won't die or anything.

[Bobcat Sig]

Not that it really matters, but a tapped hole will always have better resistance to pull-out / strength, whatever you want to call it. Definitely overkill though.

I don't have the link handy but I'll see if i can find it...

No shit? If you can find the link, I'd love to read up on it.

[Timberridge]

No shit? If you can find the link, I'd love to read up on it.

At least in human bone there is no statistical difference.

http://www.ncbi.nlm.nih.gov/pubmed/9122796

But, a tapped screw does tend to follow the pilot hole better.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2899740/

Isn't the interwebs great?

[dcpnz]

so if youve never mismounted a pair of skis it's not cause your all that good it's just that you aint been in a position where you do it enough to fuck up yet.

Truth right here.
Done at least 10 mounts at home, alpine and dynafit and haven't fucked any of em up before. Most recent one however not so good. Measured my center line off by 5mm, figured it out straight away so crossed it out and remeasured, then proceeded to tape my paper template to the wrong line and drilled. About to screw toe piece on and thinking it looked a little off center. Doh!!!!

[Timberridge]

so if youve never mismounted a pair of skis it's not cause your all that good it's just that you aint been in a position where you do it enough to fuck up yet.

or you're just higher than a ponderosa pine

[Ted Striker]

Yeah I saw that bone study as well, and I'm sure it's a hellova lot more scientific than what I was talking about. I also think this is purely academic (I've never had a back-out, and the only pull-out I've had broke the whole ski, so who knows)

The link I was thinking about was to some tests performed by someone on TT who posted here as well. The text is gone now that TT is dead, but I found his tables.

And it looks like I didn't remember it 100% correctly either.





So tapping somewhat improved the strength of a 3.6 pilot hole, and significantly improved the strength of inserts, but reduced the strength of a 4.1 pilot hole. I think (again IIRC) that in the subsequent "discussions" people postulated that the increase in strength from tapping a 3.6 hole was due to the tap cutting cleaner than the screw threads, resulting in less compression damage to the adjacent wood.

As for the 4.1 hole, I'm guessing it's simply less material left to grab - but I'm no engineer - so take that FWIW.

[Shorty_J]

Is binding glue a necessity or recommendation?

I just use regular outdoor waterproof wood glue.

I'm not a ski tech, but I did stay at a Holiday Inn Express last night.

[Shorty_J]

Interesting that an un-tapped 4.1mm hole held better than an un-tapped 3.6mm hole in a purely wood-core ski.... considering the recommendation for that ski would be the 3.6mm.

Also interesting that they only tested metal topsheet skis with a 3.6 (which is not the usual recommended).

I'll also comment with my non-scientific and limited experience with mounting foam-core skis to suggest that even though pull-out values seem similar with and without tapping in foam core skis, I would recommend tapping anyway. I've had spinners in foam more than any other material, and my hypothesis is because it's difficult to get the thread started in foam... and by the time you do you've done some damage to the thread. Either than or I over-torqued becuase I was using the resistance of wood as a baseline.

[JayPowHound]

Also interesting that tapping helped the 3.6 hole but not the 4.1 when its usually recommended for 4.1 holes in metal skis...

Makes me think maybe I should start drilling and tapping 3.6 for everything regardless of construction.

[Bobcat Sig]

[mkalynchuk]

Just wanted to say thanks to everyone for all the feedback. Some careful measurement and a slight tap with no glue and everything went really smooth.

The biggest thing was just having confidence in my measurements/center line and after the nerves wore off (once the first hole was drilled) everything else was easy. Bindings are mounted and ill be cruising this weekend no problem!

*edit* I also had a really fun fucking time and I'm sure that also counts =p

[Shorty_J]

Also interesting that tapping helped the 3.6 hole but not the 4.1 when its usually recommended for 4.1 holes in metal skis...

Makes me think maybe I should start drilling and tapping 3.6 for everything regardless of construction.

Except that a wood core with metal had a higher pullout strength WITHOUT tapping than with, for some reason.

I wonder how many samples of each scenario they took for the results...

[Bobcat Sig]

Just wanted to say thanks to everyone for all the feedback. Some careful measurement and a slight tap with no glue and everything went really smooth.

The biggest thing was just having confidence in my measurements/center line and after the nerves wore off (once the first hole was drilled) everything else was easy. Bindings are mounted and ill be cruising this weekend no problem!

*edit* I also had a really fun fucking time and I'm sure that also counts =p

But how many beers did you drink?

[mkalynchuk]

None when using power tools and drawing straight lines. However, the post-mount celebration was excellent Testing out the bindings tomorrow at Sunshine =]

[PlayItLeo]

But how many beers did you drink?

None

-10 points for failure to follow proper mounting protocol.

[Ted Striker]

Again, all of this is IIRC...

I think all of the test were performed by one person (over on TTips) and each result is an average of 3 tests. In the top chart, the number in parentheses after the core type indicates an individual ski, i.e. ski 1, ski 2 etc.

Line 4 is pretty cool. The pilot hole is wider than the screw, so that screw that is set purely with epoxy - no threads in the wood at all. Surprisingly good result there.

As for why a 3.6 pilot hole into a metal topsheet... yeah, I don't know. My only guess is that it's "wrong" and he wanted to see what happened.

When it comes to metal topsheets, I would personally stick to the recommended 4.1 pilot hole and tap (at least through the metal). It's just cleaner.

I like geeking out over this stuff as much as the next internet nerd, but it's all just degrees of good enough. Line 7 is the lowest force to pull-out, yet it's how every ski shop does it, and upward pull-outs are extremely rare (or non-existent). I've seen some lateral pull-outs, but the force there was enough to break the ski, so the mount was irrelevant.

The person who performed these tests skied tele, where this stuff is somewhat more applicable due to fewer screws and higher torque.

[Ted Striker]

with no glue

I'd glue. It prevents water intrusion.

Back when I worked in a shop, we'd occasionally replace/warranty or relocate bindings, and I've seen some rusty screws (which also means wet cores).

[~mikey b]

I'd glue. It prevents water intrusion.

Back when I worked in a shop, we'd occasionally replace/warranty or relocate bindings, and I've seen some rusty screws (which also means wet cores).

and you probably also saw some rotten wood glue

I'd epoxy.

[Cocximus]

Well... I deserve some heavy jonging for my lazyness. I had a shop mount my adrenalins and they fucked up in every possible way. All screws are crooked as fuck. Worst of all the bindings don't lift. They drilled the back plate almost 1cm off. Fuck. I am mounting my own from now on.

[Ted Striker]

@ Mike - Yeah, I like epoxy too. I should've added "at the very least"

[Cocximus]

Anyone drill overlapping holes in skis with metal topsheets? Even with a drill press the bit might bend and go in the original hole, no? I am thinking I should fill the original holes with epoxy, then redrill.

[jono]

If they overlap much the bit would be likely to flex sideways with a drill press, but you can mitigate that well by starting with a very small bit and sizing up. Still probably good to fill first, but even with a fill the metal is likely to cut differently from the epoxy so I'd probably just do both if you're using a press anyway; only takes a couple seconds to swap bits.

[Jethro]

You can also insert the bit into the chuck so that only like 1/2" is sticking out. It makes for a much more rigid drill tip.

[Ted Striker]

FWIW, this is probably what I'd do:

Ideally I'd try to find a 1/8" hardwood dowel and epoxy that in place first. Wait at least 24 hours. Then depending on where exactly the new hole needs to go, I might use a sharp punch + hammer to locate the new hole. Going that route, I'd use a regular drill (not drill-press), and drill a small pilot hole to just below the metal. If that's exactly on, I'd drill the full-sized hole. If it's off a little, I'd "finesse" it in the required direction with a small bit before doing the final drill.

Then tap, and install with expoxy.

[Cocximus]

Good tips thanks.

I think a drilling block will be key here. I can clamp it, and maybe even use a sheet of rubber between the ski and the block. That will keep the bit exactly where I want it.

Since these are adrenalins with the funky screws I am using drive-in inserts. 300 kp/662 lb pull out. What's the average pull out strength for binding freedom inserts?


So what's the consensus on what the shop should do for me? They ain't touching my skis again. I am thinking a refund, cost of inserts and maybe some shop supplies at cost. Sleeziest part was they they just gave me the skis back wrapped up. WTF did they think? I won't notice the heel does not lift?