Mounting ski bindings - screw tap question

[everest8850]

The common information on non-metal laminates skis is that the most commpn bindings need a 3.6mm drill bit (I use a 3.5mm bit - no issues) and a "AB" screw tap to get the screws to bite into the wood without too much 'volcano-ing' when you drive the screws in. However, almost all the screw taps I see sold on my side of the planet are in metric and none seem to share information on the thread pitch. A TG forum post mentioned that the closest would be an M5.3 type screw tapbut al I have seen are in whole number ge M3, M4, M5. Anyone can shed light on what metric tap works best?

 

[Tricia]

According to all of your previous posts, you're not leveraging the skis enough to worry about this kind of detail.

 

[everest8850]

According to all of your previous posts, you're not leveraging the skis enough to worry about this kind of detail.

I have to mount my own skis, so just concerned about getting the right kind of screw tap. I have heard however, some folks self mount without bothering to use a tap

 

[KingGrump]

The easiest thing to do is to order a #12AB tap from any alpine gear supply site off the web.
If you are at a place where Brown or their counter part do not frequent, go to the local ski shop and buy one off them. You may have to pay through your nose for it.
IIRC, you are in Japan. They are pretty current with tech there. So life shouldn't be that difficult.
On top of that as @Tricia said, you aren't stressing the skis enough to stress about details like this.

But if you insist.
On a ski with a layer of metal on top, the taping creates a threaded hole through the metal layer for the screw to engage with. Compression of the ski core by the screw probably add something to the retention value but The engagement of the threads between the metal layer and the screw probably provide most of the retention strength.
On a non-metal ski, compression of the ski core by the screw will provide most of the retention strength. If you tap the core prior to installation of the binding screw. This compression value is lost. You will be dependent on the shear value of the tapped thread for retention. Keep in mind the threads you just tapped is wood.
My opinion is so long your binding is sitting flat and in good TIGHT contact with the ski, all is good. A bit of mushrooming doesn't affect much.

Don't have any scientific and/or engineering studies to validate any of this. Just plain old common sense.
I am sure the binding companies have tons of test/studies on this stuff. Give them a call.

And if you still insist. Here is a quick pass in jury rigging. Sorry, I mean field improvisation.
To keep the top sheet from volcano-ing. Bevel the hole LIGHTLY with a countersink. Just keep in mind the top sheet on most skis that do not have a metal layer on top will be expected to contribute to the retention value of the binding screws. So DO NOT cut too deep with the countersink.
If that still doesn't make you happy. Take a long spare binding screw and file one or two vertical slot in the thread from the tip of the screw with a small triangular file. Make sure to remove the burrs from the screw thread as a result of the filing. Voilà, a home made tap.

If all else fails, do what MacGyver would do - get out the trusty Swiss army knife.

 

[François Pugh]

I bought a tap and die set years ago. I used it a few times, and haven't looked at it lately, so my memory may be off. However, I seem to recall that it came with a thread guage- sort of like a set of feeler guages, but with saw-toothed blades. Line up the teeth on the right blade to the threads and the guage is given on the blade.
Never mind my explanation - just google thread guage tool.

 

[KingGrump]

A #12AB tap is same as M5.3 x 1.81 in metric.

If you order a SVST #12AB tap. This is what you'll get.

Life shouldn't be this hard. Unless you want it to be.

 

[Tricia]

I have to mount my own skis, so just concerned about getting the right kind of screw tap. I have heard however, some folks self mount without bothering to use a tap

I may regret asking this but, why do you have to mount your own skis?

On top of that as @Tricia said, you aren't stressing the skis enough to stress about details like this.

This^^^

@everest8850 I fear that you're stressing about things that have the potential to suck the fun out of your skiing experience.
Take a deep breath think snow!

 

[Doug Briggs]

You do not need to tap skis that don't have a metal top sheet or mounting layer. You DO need to tap any ski that has a metal top sheet. You can tap a ski without metal to help prevent volcanoing. No more than three turns are required in either case. You don't tap the entire hole, just the top sheet in either metal or non-metal case. You are making the threads for the screw in a metal sheet so it won't delaminate the ski during the screwing-in process. You do it for non-metal skis to reduce volcanoing.

If you don't tap a non-metal ski and there is volcanoing of significance, you'll know because you can see between the ski and the binding; there will be a gap. If there is, just back out the screws, file or scrape off the volcano and CAREFULLY re-screw the bindings to the ski.

ANY TIME you reuse an existing hole in a ski you want to place the screw in the hole, slowly turn the screw backwards (lefty loosey) while gently pressing down until you feel the threads of the screw settle into the threads of the ski. THEN you can start screwing the screw back in (righty tighty).

ALWAYS use a waterproof glue when mounting. It keeps moisture out, helps retain the screw (you'd be amazed at how many screws are loose in bindings I see in the shop) and provides a more positive interface for the screw/ski interface.

 

[cantunamunch]

You do not need to tap skis that don't have a metal top sheet or mounting layer. You DO need to tap any ski that has a metal top sheet. You can tap a ski without metal to help prevent volcanoing. No more than three turns are required in either case. You don't tap the entire hole, just the top sheet in either metal or non-metal case. You are making the threads for the screw in a metal sheet so it won't delaminate the ski during the drilling process. You do it for non-metal skis to reduce volcanoing..

This^^^ , and this:

On a non-metal ski, compression of the ski core by the screw will provide most of the retention strength. If you tap the core prior to installation of the binding screw. This compression value is lost. You will be dependent on the shear value of the tapped thread for retention. Keep in mind the threads you just tapped is wood.

 

[Eleeski]

For a non metal ski, my trick is to heat up a screw (not red hot but warm enough to soften the resin) and tap with the screw. This taps the pre drilled hole (properly sized) without deforming, cracking or too much cutting. Some JB Weld for the final assembly and it's pretty durable.

I've pulled a few screws out (both snow skis and waterskis - more waterskis). If the core is foam or honeycomb, I pick out the foam from under the top skin to make a small void there. A mix of JB Weld and steel wool fills the hole and gives a decent grip on the screw. When it cures, the repair is pretty good. I pack it pretty tight so I probably don't need to heat it and turn it upside down but I usually do anyhow.

The steel wool epoxy trick works well on wood core skis as well. I just don't pick at the hole.

Inserts aren't that popular on snow skis. On waterskis, adding inserts in place of a pulled out screw allows a like new installation as the inserts are a bigger diameter so your pre drill cleans out to fresh material.

I know there are a lot of binding hole patterns and placements but it sure seems that engineered inserts could work for snow skis. Standard mounting with adjustment options would be magic!

Eric

 

[oldschoolskier]

This is a bit more a industry specific tap. Standard sizes in metric or imperial will not work.

Buy the one suggested, BTW I believe there are a couple of other ones though rarely used.

 

[everest8850]

Hey folks - thanks for all the fabulous advice on the art of tapping! For Tricia - I have do most of everything as I am in Singapore and there is no ski shop, proshop, demo days - heck , we dont even have snow. I did mount my last pair at a shop in Japan though, but thought Id better learn how to do these things myself as I'm still in an experimental phase of working out what works best with my current lower leg disabilities. And yes, it looks like the #12AB sold at Tognarworks and Slidewright are the best choice as its not just the bore diameter that matters but the thread pitch as well. I will probably go with the light countersink , and use the screws to tap into the holes themselves approach as my skis are all non-metal..... Once agains thanks folks...

 

[KingGrump]

Didn't realize you were in Singapore. That is a tough part of the planet to get ski stuff. Apologies for my tone.

Good luck with your mount.
The first one is the hardest. It's a breeze after that.

 

[Uncle-A]

You are making the threads for the screw in a metal sheet so it won't delaminate the ski during the drilling process.

I must be missing something, do you mean the "screwing process" not the drilling process? Otherwise are you trying to make threads in a hole that hasn't bee drilled yet?

 

[Doug Briggs]

I must be missing something, do you mean the "screwing process" not the drilling process? Otherwise are you trying to make threads in a hole that hasn't bee drilled yet?

Yes, you are correct. I'll fix that in the original post.