Drill Bits -> why is there a 4.1 x 9mm and 9.5mm ?

[ARL67]

@tomahawkins has made it too easy with all the info to mount my own bindings, so I am going to give it a go for 2 incoming sets of flat skis. I'm a life-long tinkerer, with a well-equipped workshop at home ( golf & ski ), a drill press on hand, etc.

I'm adding to my cart at Tognar and am curious as to why we have 4.1 x 9mm and 9.5mm drill bits ? Surely I don't need to buy both -> should I err on long or short ? Nothing like fretting over 0.5mm

 

[Dwight]

Standard is the 4.1 x 9.5mm.

Product Details - SlideWright Ski & Snowboard Tools, Wares & Tips

Alpine & Nordic Binding Mounting Drill Bits

www.slidewright.com

Highly recommend the following if you are doing your own mountings.

Products - SlideWright Ski & Snowboard Tools, Wares & Tips

Binding Mount Jigs, Guides and Clamps

www.slidewright.com

Printables

www.printables.com

 

[firebanex]

Don't forget the 3.5mm bit too, for skis without a metal layer.

Go slow, triple check your marks prior to drilling. I bust out a digital caliper to make sure the marks are centered on the ski as measured from the metal edges, not the topsheet!

 

[DesmoDog]

@tomahawkins has made it too easy with all the info to mount my own bindings, so I am going to give it a go for 2 incoming sets of flat skis. I'm a life-long tinkerer, with a well-equipped workshop at home ( golf & ski ), a drill press on hand, etc.

I'm adding to my cart at Tognar and am curious as to why we have 4.1 x 9mm and 9.5mm drill bits ? Surely I don't need to buy both -> should I err on long or short ? Nothing like fretting over 0.5mm

IMHO they're the same bit if you take tolerances into account.

I bought the longer one myself and would be willing to bet that if you took a home installer, drilled 50 holes with each bit and then measured them you'd never be able to tell which bit drilled which hole.

 

[Henry]

I use a separate countersink to remove the burr at the top of the hole that the supposed built in countersink on the shoulder bit didn't remove. Tapping the hole gives a cleaner stronger screw grip even if there is no metal plate to thread. A puff of compressed air into the hole (if you have the air) gets the chips out easily. The 4.1mm bit is also the right one for skis without a metal layer but do have a metal plate built in for mounting the bindings.

If you have any doubt in the mounting process first mount the bindings on a piece of 2x4. If that turns out just right, you'll feel better about drilling into your new skis. Oh, keep track of the shovel end of the skis and the front end of the bindings.

 

[SlideWright]

Standard is the 4.1 x 9.5mm.

Product Details - SlideWright Ski & Snowboard Tools, Wares & Tips

Alpine & Nordic Binding Mounting Drill Bits

www.slidewright.com

Highly recommend the following if you are doing your own mountings.

Products - SlideWright Ski & Snowboard Tools, Wares & Tips

Binding Mount Jigs, Guides and Clamps

www.slidewright.com

It's better to be deeper with your drill hole than the screw length than shorter to avoid base dimpling and/or not being able to mount the binding tight to the top sheet. A quick check is to make sure the screws are in your bindings, flip them over and simply measure the protrusion of the screws and/or compare them to the tip of your stepped drill bit or to set your drill stop.

Pertinent to the OPs question, along with related issues from the link above:

• 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 (ie, 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.
• The 0.5mm difference between a 7mm vs 7.5mm or 9mm vs 9.5mm is negligible and the bits are interchangeable. (0.5mm is about the thickness of 5 sheets of paper.)
• Make sure this will not exceed the thickness of the ski or snow board.
• 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 topsheet type or drill tip diameter is recommended. The same tap works for 3.5mm & 4.1mm diameter holes.
• Long shank alpine drill bits are 1 3/4" (4.5cm) longer than standard bits for use mounting jigs and drill guides
• Armada skis require a Double Step bit from 4.1 to 3.5mm.
• NOTE! A double step bit might be the only drill bit you need. Not only is the 4.1mm tip needed for metal and carbon top sheets, the extra diameter might reduce 'volcanoing' on plastic and other top sheet materials.

Additional info can be found in our tuning tips, starting w/Drilling Skis to Mount Ski Bindings