ski binding mounting question - Drill bit size?

**DEVO** · 10-26-2007, 09:18 AM

Why is it recommended to use a 4.1mm bit instead of a 3.6mm bit when the ski has a sheet of metal? I am getting a 3.6mm bit and was planning on using it to mount bindings on a new pair of Scott P3's, which has a layer of titanal. Can I still use the 3.6mm? What happens if I don't use a 4.1mm instead? I guess I am confused as to why a ski with a layer of metal need a larger diameter hole for the same size screw?

**GrizzlyFD** · 10-26-2007, 09:22 AM

Harder to screw the smaller hole

It will work, but it will be harder to screw into the metal sheet. Just use a 5/32" bit (which btw is 4.0mm).

**pechelman** · 10-26-2007, 09:23 AM

ever measure the root diameter of a binding screw?
its bigger than 3.6mm.
furthermore, since the topsheet is metal, it can better retain the screw with a larger diameter.

on the wood only, its better for it to be a bit more snug.

**DEVO** · 10-26-2007, 09:37 AM

ok, I think I will just get a 4.1mm bit as well. Thanks!

One more question, how important is it to tap these skis first?

**Conundrum** · 10-26-2007, 09:37 AM

If there's metal, use a 4.1. When you use 3.6 with a metal topsheet, the hole isn't big enough. So, when you screw the screws in, it can actually pull the metal layer up a little. This can cause the binding to not sit flat and that's bad.

Sometimes you can get by wtih a 3.6 but I wouldn't risk it.

Also, tapping the hole can help too. I always tap the holes in metal topsheets. Volkl used to not require it in their metal topsheets but it never hurts.

**DEVO** · 10-26-2007, 09:39 AM

That answers my tapping question. So drill, then tap with a #12 tap? Is a #12 ski tap (listed on Tognar.com) the same as any #12 tap?

**weibo** · 10-26-2007, 09:46 AM

I think the size is the same but the threads always seemed different on a ski tap compared to a standard tap.

**squirrelmurphy** · 10-26-2007, 10:08 AM

This is probably blasphemous, but i've gotten by a couple times by tapping the hole with one of the screws i am about to use. I figure if you don't have the binding on the ski, there's nothing for the screw to pull against and the topsheet should be fine.

*but now i do have a #12AB tap and use it, and it is worth the $12 from tognar

**Voltron** · 10-26-2007, 03:21 PM

Originally Posted by squirrelmurphy

This is probably blasphemous, but i've gotten by a couple times by tapping the hole with one of the screws i am about to use.

Really not all that blasphemous; the screws are self tapping after all. The only must tap instances I've seen are with some metal race plates (Vist).

**GrizzlyFD** · 10-26-2007, 03:33 PM

^^^ agreed. While I don't believe binding screws are completely self tapping, they do bite into the skis very well. I've always been hesitant to tap holes that screws are meant to go into, as opposed to bolts. Screws rely on the thread friction to produce tension between the screw head and ski.

**wheels** · 02-07-2010, 08:38 AM

This place is a wealth of information Just getting ready to mount up my Super Bros, and had this exact question

**haydukelives** · 02-07-2010, 11:01 AM

can someone please explain why a single drill bit should be $15? (at tognar)

**Boddysurfer** · 02-07-2010, 11:38 AM

Originally Posted by haydukelives

can someone please explain why a single drill bit should be $15? (at tognar)

Cuz "retail is for suckers"-Krammer

A 5/32" bit is a buck fifty, and works great in my drill press.

**Boddysurfer** · 02-07-2010, 11:51 AM

Originally Posted by weibo

I think the size is the same but the threads always seemed different on a ski tap compared to a standard tap.

That's because many screws are the same diameter, but not necessarily the same TPI (threads per inch).

Make sure your tap is the same TPI as your screws. If you lay your screw against the tap and they line up and mesh, your good.

**buttahflake** · 02-07-2010, 12:50 PM

it's called volcanoing the topsheet when the screw pulls on metal. use the 4.1 and always tap metal skis.

**wooley12** · 02-07-2010, 01:27 PM

Don't have a picture now but a tap has grooves or flutes running across the threads to catch excess material. I made my own tap by using a tapered triangular file to create 3 flutes in a long extra mounting screw I had. Locked in vice grips it works like a charm. Use it like any tap, 2 turns in and one turn out. Repeat.

**Diamond Joe** · 02-07-2010, 01:58 PM

Originally Posted by DEVO

..was planning on using it to mount bindings on a new pair of Scott P3's

Not to jack your thread, but where are you planning on mounting?

[ame="http://www.tetongravity.com/forums/showthread.php?t=184500"]Mounting point (Scott P3s) - Teton Gravity Research Forums[/ame]

**dima** · 02-07-2010, 03:26 PM

Originally Posted by haydukelives

can someone please explain why a single drill bit should be $15? (at tognar)

Some people can get away 5/32. I bought a 3.6mm bit so I don't have to worry about depth on every hole, and all the skis I mount a wood. Its a $15 that will last a REALLY long time if you use/store properly.

They actually take a endmill and grind it down to the 4.1mm or 3.6mm size with the correct length. I imagine thats where the cost comes from.

I never tap, though I sometimes pre-thread before putting in epoxy. I drive the screws in with and electric driver and it works great.

**Jaxson** · 02-08-2010, 02:29 PM

How about this: Drill first with a 3.6. Then just through the metal with a 4.1. Run your tap in through the metal sheet and the hole is ready.

I've also noticed with a tapered tap it tends to open up the metal part of the hole as you make more turns so you may be able to get away with a 3.6 if you tap. Comments anyone?

**skimaxpower** · 02-08-2010, 11:59 PM

Originally Posted by buttahflake

use the 4.1 and always tap metal skis.

YES. Totally correct.

Look guys. Just follow the instructions. If you're asking yourself "can I get away with just..." the answer is probably no: you cannot.

**jondrums** · 02-09-2010, 02:17 AM

Originally Posted by DEVO

That answers my tapping question. So drill, then tap with a #12 tap? Is a #12 ski tap (listed on Tognar.com) the same as any #12 tap?

no its not the same. the ski tap is #12AB, which is some kind of thread designation I've never seen referenced in any standard. I believe it is some kind of wood-screw thread. Bottom line, you can't find this tap at a hardware store - only at ski tool specialty store.

**axebiker** · 02-09-2010, 08:02 AM

The P3 does not need a 4.1 or tapping. I mounted a pair recently using a 3.6 with no issues. I don't recall any metal in this ski.

**skilife** · 12-16-2014, 07:26 PM

By CE regulation, all current skis have the recommended drill size printed on the ski, either in the mounting area, on the adjacent sidewall or on the tail with the ski dimensions. If there are no drill sizes provided on the ski ( i.e. custom skis), contacting the manufacturer for their recommendations is your best course of action. If unsure, drill with 3.5mm diameter tip. If metal is present, then use a 4.1mm bit.

The general rule on alpine ski drill bit sizes is 3.5mm for non-metal skis and 4.1 for metal. There are exceptions, such as a metal binding plate in a non-metal ski, carbon fiber top sheets, etc.

The outside diameter of an alpine screw thread is just over 5mm. The inside diameter of the screw thread (shank) is just over 4mm which matches the tip of a 4.1 diameter bit. Softer materials such as wood or plastic will compress when driving a screw into a 3.5mm hole. Non-compressible materials like metal and carbon should be drilled with the larger diameter, 4.1mm hole so the shank does not compress and damage the material while being driven into the ski.

Binding Freedom & Quiver Killer stainless steel inserts & heli-coils require a 1/4" tipped bit.

The minimum depth for a screw for a binding mount is 6mm/1/4". Measure the screw less the binding thickness will provide you minimum drill tip length.

It is better to err towards a longer tip than one shorter than the embedded screw section length so the bindings can lay tight to the ski.

Make sure this will not exceed the thickness of the ski.

The excess depth of a hole deeper than the length of screw will be filled with the glue.

Tapping skis with metal and carbon top sheets using a 12AB tap is recommended. Tapping all holes regardless of top-sheet type or drill tip diameter is recommended. The same tap works for 3.5mm & 4.1mm diameter holes.

**skimaxpower** · 12-17-2014, 12:50 AM

^^ Wow. Thanks for dredging up a 4-year-old thread.

**Knut** · 12-17-2014, 09:57 AM

Originally Posted by skilife

The general rule on alpine ski drill bit sizes is 3.5mm for non-metal skis and 4.1 for metal.

Ehrm.... To my knowledge, that's 3.8mm and 4.1mm respectively (although 3.6mm can be found, too). In both cases 9mm deep, not 6mm. For some Kids skis/bindings, 6mm might be fine, but for all others you'd ruin the mount by severe volcano eruption.

So congrats for digging up a 4 year old thread to get it just about not entirely exactly to the point right.