How Many Holes can you Drill in a Ski?

Drilling holes in a ski, especially as a DIY process can be nerve wracking. But once you get the hang of it, it’s not so bad, or stressful. But the question remains, how many holes can you, in fact, drill in a ski and maintain the ski’s integrity? Lou Dawson has some thoughts.

Editor’s Note: We’ve enlisted Lou to, once again, provide an update on the eternal flame of DIY questions, how many holes can you drill in a ski? Below Lou’s words, we’ll include notes from some ski manufacturers regarding the how many holes can you drill in a ski question. The last version of this post was published in 2015.

There is a traditional view in ski culture that drilling extra binding holes devalues a ski and weakens it to the point where one should be cautious about using it hard. Being cautious might still hold true for large aggressive skiers using non-release telemark bindings or DIN 16 touring binders set to max. Otherwise, read on — you can drill a bunch of holes in most skis (though some ski models are known to be weak and indeed should only have one set of holes).

Thanks to the needs of telemarkers, many, if not most, of today’s backcountry touring skis have an incredibly beefy reinforcement in the binding mount area. (Though a recent trend has been to back off from this to save weight, so be sure to research what you’ve got). More, nearly all modern skis are overall super strong (the operative word being “nearly,” as any shop employee or ski tech can testify to). I’ve skied for years on planks Swiss-cheesed with up to four sets of binding holes and never broken a ski under the foot or had a binding rip out under normal use. (Take note, I’m not an aggressive skier, don’t fall that much, use release bindings set to release, and mount bindings using the methods detailed below.)

No Overlapping Holes

Mechanical Jig: So, how to do the deed? Lay out your new binding holes on your backcountry skis. If using a mechanical jig, look down through the drill bushings and check how close the jig’s holes align to the existing holes; ideally, if you are a minimum of 1cm away from the existing holes, great. Once you decide on a position, drill at will.

Paper Template: If using a paper template, punch out the screw locations with a paper hole punch so you can slide the paper around and see how your new holes relate to the existing ones. Once you decide on a position and it’s confirmed the new holes will be a minimum distance from the old holes, re-mark with a centerpunch and drill.

If the new bores don’t overlap the old holes, ensure the template is taped in position, remark with your centerpunch, and drill away.

If the holes don’t overlap but are super close to your new ones, still fill the old holes with epoxy steel and steel wool. Otherwise, fill the holes with regular 5-minute epoxy, or use the plastic plugs available from ski shops.

As for the plastic plugs, they seal the holes just fine, but are not preferred because when drilled out the remaining plastic in the hole may not bond to epoxy. We usually fill our holes with epoxy or urethane glue if there is a chance we’ll be drilling them out again. For temporary sealing, I just put duct tape over them. Once in a while we use the plugs.

Overlapping Holes

If you’ve got an overlap situation, read on.

If any new holes overlap an existing hole by only a few millimeters, try moving your binding location accordingly, usually rearward for recreational and backcountry skiing.

Most touring bindings have enough heel unit adjustment to tweak, so they’ll always miss existing holes; it’s the binding toe you might have to move back a hair. A small change in boot fore/aft location is totally within spec for ski performance, and as long as the edges of your new holes are a few millimeters from the old (ideally about a centimeter), and the ski has a reinforced binding mount area, you’ll be fine drilling and using the new ones.

What to do with the old holes?: Fill the old holes, but a quick job with plastic plugs or 5-minute hardware store epoxy will suffice.

Prepping Old Holes when New Holes will Overlap

Option One
Step1: If your new holes must overlap the old ones, then you need some careful fill work (or best, do everything possible to avoid overlaps). I usually fill the old holes with something like JB Weld or epoxy steel, and poke steel wool in the hole as well. It’s essential to fill the holes completely with some sort of hard filler; do so by poking the epoxy and wool in with a small probe such as a tiny drill bit. Use the slower curing epoxy as it’s stronger than the 5-minute versions and produces less heat. Wait 48 hours at room temperature for a full cure before the next step.

Step 2: After the epoxy hardens in the holes (48 hours at room temperature), I smooth it off with a sanding disk in a grinder. Whatever works for smoothing is fine; just avoid anything but cosmetic damage.

Step 3: The Drilling— Drilling overlapping holes is the tricky part. If the ski lacks a metal layer, start the drilling with a small bit, then step up through successively larger bits to your final size. The idea is to prevent the edge of the existing (new) hole from forcing the bit to the side. The objective is to only drilling into the edge of the hardened epoxy in the old hole. (To visualize, a portion of the new hole will have hardened epoxy as a portion of its outer edge.

Dealing with a metal layer is tougher. If your drilling begins in the metal, stepping up the bit sizes will usually work. If you start in the epoxy fill, do the step-up routine till your bit encounters the metal edge. Then, instead of going to the next size bit, pull the drill most of the way out, then hold the spinning bit against the metal edge so it eats sideways a small amount in the direction the hole needs to grow, thus “egging out” the hole. Beware the heat this can create, which can destroy your epoxy and damage the ski where you need strength the most.

We’re talking a millimeter or less of this, so no big deal. If you’re a craftsman and have a rotary grinder (e.g., Dremel), you can “egg” out the holes using a small rotary cutting bit, which works much better. Take care not to “egg” too far. Keep it tight.

Finish the hole with the correct size bit. Don’t fret if one or two of your holes end up slightly off the layout, as tech bindings have a small (perhaps a millimeter) amount of tolerance for off-layout screws. (If some of your holes are off-layout, place screws in on-layout holes first, then place others.) Need clarification on this sentence. ((Lou edited, forgot to turn on the “suggest” feature.))

The Redo: If you mess up and end up drilling the epoxy out of an old hole, re-fill and try again with a bit of side pressure while drilling. Tap the holes if you’ve got a ski mounting tap, place all binding screws with the same long-cure epoxy you used to fill the existing holes, don’t over-torque, let cure for 48 hours, and you’re good to go backcountry skiing!

Note, it’s possible the epoxy used for your final screw placement can soften the epoxy fill in the original holes. One reason for using slow cure epoxy is the lack of heat, which can soften existing epoxy or ski resin layers. I recommend saving a blotter with the cured fill epoxy on it and smearing some of the screw placement epoxy on the original. You can thus observe any problems.

 

Option Two for Filling/Plugging Old Holes: Another method of filling old holes for redrilling is to epoxy hardwood plugs into the holes, then drill and tap. This method has advantages as the plugs can be more structural than the epoxy and steel wool method. The wood, however, is super sensitive to moisture, so use epoxy every step of the way. And cover them with epoxy when you do the final binding mount for 100% defense against water.

Option Three: Yet another technique is to carefully bore holes for inserts such as Quiver Killer. Whatever the case, if you have access to a milling machine or high-quality drill press, drilling overlapping holes can be done much more easily by clamping the ski to the machine and boring holes that are forced into perfect position by the rigidity of the machinery.

Note about taping holes and bit sizes: Ski shops use special drill bits for drilling skis, usually 4.1 mm for skis with metal layers, and 3.9 mm for skis without metal. If you mount a lot of backcountry skis, it’s a good idea to purchase ski-mounting drill bits. Along with such bits, buy a threading tool (tap) to thread the holes. In my experience, it can be okay to use a slightly larger 5/32 inch drill bit for the final size hole without a tap. But when you don’t use a tap, you risk the binding screw augering the JB Weld out of the hole and reversing all your hard work.

If you choose not to use a tap, especially with non-metal skis, use plenty of pressure to twist the screws in so they start to thread immediately. Don’t over-tighten and strip the holes, and indeed use epoxy in the holes when you place the screws.

To remove epoxied screws, lightly heat the screw with soldering iron before twisting out.

We’ve gone to 11 on the how-to, not the how-many. The answer to the original question, “how many holes can I drill in a ski?” is that it depends.

Using pre-existing holes twice: This should not be a problem so long as the original screw/s were not overtightened when installed. If the original screw was over-tightened, you may have stripped the hole, and an insert may be required. If the screw was not overtightened, sink the screw while using a bit of epoxy.

In most cases, you can use the same holes quite a few times but they do deteriorate a bit each time. If you use epoxy each time the screws are sunk, and then heat the screws when removing, you can do it dozens of times. Remember, the key is to not over-tighten but to still, tighten enough. This requires a “feel” for appropriate tightness.

Okay… how many sets of holes can you get away with? Let’s call it three , each roughly a centimeter apart . Thus, a 4 hole binding toe, three times, 12 holes. This is doable, given the old holes were properly sealed and there’s no water damage. Beyond that,drilling a fourth set of holes moves the ski in the direction of ski furniture. Also note that some modern lightweight skis do not incorporate a metal sheet in the binding mount zone. In that case drill with caution and care, seal the old holes well and reassess the ski’s integrity each time you drill. Note, if you see any corrosion when backing out an old screw, assume water has seeped in and damaged the ski.

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Editor’s Postscript on the 1cm distance between old and new holes. Back in 2012, not exactly the pleistocene, but for some, that might seem long ago, Black Diamond conducted a basic test to determine the optimum distance between old holes and newly drilled holes. (Distances between holes were measured center to center and no glue was used to retain the screws. Click the link to see other test parameters.) BD comes up with a minimum of 7mm between holes. We’re bumping that out 3mm, for an even 1cm. Needless to say, we are not applying the ~1cm rule for overlapping holes.

We also sent the following questions out to several ski manufacturers.

1) Recommendations for the distance between new holes (no overlap with old holes) when redrilling a ski?
2) WildSnow does offer some advice on drilling overlapping holes.
— With no metal layer in the ski, do you recommend skiers not go down the path of having overlapping holes?

Here are the responses received to date.

DPS Response

(Shop for DPS skis)

Question #1: Recommendations for the distance between new holes (no overlap with old holes) when redrilling a ski? Be as specific as you would like; do the specs differ for the toe and heel?

Here at DPS we are extremely conscious of our environmental impact. While we must manufacture and sell skis to stay in business, we take pride in our constructions and the fact that our carbon skis have a prolonged flex life. With that said, we want you to love your skis and we want them to last you a long time. Should they need to be drilled multiple times, we have some tips for you.

– We require one hole diameter spacing as the minimum distance between two holes. How many times can this be done? We feel drilling any more than four sets of hole patterns is excessive and will likely affect your ability to land on your ideal mounting point.

– It’s also important to remember that initial downward screw torque is crucial to long-term strength. Loose screws fatigue the reinforcements and will eventually lead to failure. Additionally, if you are planning on reusing your screws, it’s extremely important to thoroughly clean each screw as old material left in the screw can wallow out your new holes and reduce strength.

– There are many factors that play into how many times you can, and should redrill a ski. Before making any final decisions, we recommend visiting your local DPS retailer for advice.

Question #2: With no metal layer in the ski, do you recommend skiers not go down the path of having overlapping holes? (This question might not apply to all ski manufacturers.)

We do not recommend ever drilling overlapping holes.

Blizzard Response

(Shop for Blizzard skis)

Our 2 cents would basically just follow the recommendations of the ISO G1 adult mounting norms so no overlapping holes and at least 1cm between each hole whether new or old. It is also important to fill the old holes with something to prevent water ingress, ideally gluing in a plastic plug that many places sell (Winterstieger being one).

All our adult skis conform to the G1 adult norm so have the same pull out forces (regardless of Bonafide or ZG), all with at least one titanal mounting sheet underfoot.

Response from Duncan Pawson, Product Development Engineer at G3

(Shop for G3 bindings)

This is a common question with no correct answer (depends on screw size, and construction of the ski). That said, 10mm between the centre of holes seems to be the most common. BD did some tests in their lab measuring the strength reduction in having redrilled holes too close together and concluded that 7mm between holes does not affect pullout strength. This depends on the skis/screws they used, so I’d say 10mm is a safer standard. I would guess that having metal layers, would reduce the chance of crack propagation and you could probably get away with less – but wouldn’t recommend. Old holes should also be filled with epoxy to reduce any crack propagation. Often, in engineering you have a standard of hole diameter *1.5 for distance from a drilled hole to an edge. You could potentially apply the same principle between two holes in a ski. For a 4.1mm diameter screw – common in bindings – this would be a centre to centre distance of 6.15mm. Throw on a safety factor of 1.6 and you have 10mm between holes. Though, again, it depends on the materials. Wood/composite is more likely to crack, whereas metal is less likely.

Link to BD study.

I would say as long as the screw bites it’s probably fine to reuse previously drilled holes. With a metal layer this should be fine. With wood, it depends on the density of the wood. Harder and more dense woods are likely also fine. Sometimes you’ll run into the issue of redrilled screws spinning in place. This can be fixed by adding epoxy, although this will set the screw in place and you won’t be able to remove it. I’ve done some pullout tests on previously drilled holes with a titanal layer and the pullout strength was similar to screws drilled for the first time. I imagine if there is no metal layer and the screw is not biting properly, then the strength would be reduced.