Understanding Variables In Base Structures

Working with machine structures on skis, there are only a few variables that can be adjusted to influence the performance of the ski. Primarily these variables are depth, spacing, interruption, and patterns.

The structure on the ski base is primarily a closely spaced lengthwise pattern of micro-grooves. Depth of the grooves varies from about 0.01mm to 0.05mm or more. Spacing of the grooves can be anywhere from 0.25 mm line-to-line and wider.

Some structures, such as those prepared on the Mantec Skinumericontrol 140, can have line spacing and depth that vary from the edges toward the middle.

Depth of the micro-grooves is critical, and can work for or against the speed of the ski. In large-grained and transformed moist snow, deeper grooves resist propagation of moisture and help to prevent the sticking due to adhesion. However, in dry fine-grained snow, deep grooves create opportunities for increased interlock friction - the fingers and features of the fine snow grains catch in the grooves. This type of friction can be imagined as being like velcro - it can be a noisy and slow experience when deep patterns are used on fresh, cold, dry snow.

Less obvious is the influence of interruptions in the micro-grooves. Interruptions in the long length-wise grooves are important to minimize capillary propagation of adhesive layers of water. In addition, the interruptions help to keep the ski from “tracking” into the snow, and help with release of the ski; this is especially noticeable on skate skis, but at the same time is more subjective and harder to quantify.

Pattern in the structure is typically the result of interruptions (also referred to as interference, or cancellation) being organized in a predictable and orderly way. Often these patterns can be visually seen as diagonal bands or chevron shapes on the ski sole. Some structures that have varying line spacing may show a curved interference pattern. Although the patterns may be at an angle, looking closely you’ll see that the bands are comprised of cancellations or interruptions in the lengthwise grooves, and are NOT diagonal cuts in the ski base.

Interruption or cancellation profiles that cross the ski horizontally and repeatedly (perpendicular to direction of travel) are a negative influence on performance. Thus, designing an organized interruption pattern is important in optimizing the glide properties. Pattern angles of 30 degrees or less are almost never seen. Also, the repetition rate of the interruption pattern affects the performance of the ski (rep-rate can be measured in spacing across the ski).

Nordic Ultratune uses the Mantec grinder . With the Mantec the variables of spacing, depth, interruption and pattern are analyzed with built-in software features. The Mantec offers unmatched precision and control.

Each winter, designing and testing structures is an integral part of my work. Within the limits of each variable, there are infinite opportunities for optimizing the structures. Testing the structures on snow is the biggest limiter in developing effective new grinds. At Nordic Ultratune, designing structures with varying spacing, depth, and groove interruptions is the key to building a set of grinds that will work in a broad range of snow conditions.

The key to fast skis is to have base surfaces prepared with with structures that are fast and versatile enough to handle a broad range of conditions.

Stone grinding work continues weekly through the whole season.   Ultratune provides same-week turn-around during fall and winter.   Skis that arrive by Thursday will be ready to ship back to you on the following Monday.

Pick a grind, fill out a work order form, and ship your skis.

Rack 'em up.

It is busy at Nordic Ultratune in November.  Stone grinding is the best way to prepare your skis for specific conditions you'll encounter this winter.      The vast majority of the skis that arrive by FedEx and UPS right now are being prepared for the upcoming ski weeks at West Yellowstone and SilverStar, and for the early SuperTour and NorAm events.

There is still time to get stone grinding before Thanksgiving.    Check out the stone grinding selection guide.  Download a work order form (click here).   Skis that arrive by Thursday ship back out on the following Monday, just 4 days later.  Every week.

A View of the Process

Torin Koos came into the shop a couple of times while I was working on his skis in September.    He brought a camera with him and asked a few questions.    It was casual, with no script, no prepared questions, and certainly no rehearsal.

The video clip is Torin's concept, and his production entirely.    I think it's good because it shows his view of what's interesting and important at Nordic Ultratune.  Take a look!

I think the video clip is informative.      While it isn't a complete description of what is done with each pair of skis, it does give you a good idea of the process and technology. 

A big thank you goes out to Torin.     Check him out at the Methow Olympic Development site.   Or at Torin's blog with FS.      Or at his blog with In The Arena

Spring Skiing and Summer Service

There was great spring skiing at Sovereign Lake Nordic Center (at Silver Star, or Vernon BC) this past weekend.

Several juniors from MV Nordic, plus Brian Gregg and me and my wife, Margaret, took the trip. Grooming was excellent, and the snow coverage was super. It was prototypical spring conditions, with firm track in the early morning that softened by noon.

As you can see from the pic of Margaret, the vibe was very casual and relaxed. Classic skiing on "rub-skis" (a.k.a. zero skis) was terrific in the soft, moist, snow if the late morning.

After 6 weeks off of snow, it was good to get a few days of skiing! I think there will be another opportunity in Bend, OR (Mt Bachelor) in June, too.

Summer Stone Grinding

Stone grinding work continues through the summer. Naturally, the pace and schedule are a bit more relaxed. Typically the turn-around in the summer is a couple of weeks instead of the same-week service that Ultratune provides during fall and winter.

Pick a grind, fill out a work order form, and ship your skis.

Here's a little video clip showing the Mantec grinder at work at Nordic Ultratune.

Like Christmas in mid-January

It was almost like Christmas! A package arrived on Friday from Italy. A new grinding stone and some maintenance parts for the Mantec grinder.

With the new grinding machine I've been doing lots of grind testing and have really been cutting through a lot of stone. I'm not anywhere near the end of the current wheel, but it is definitely nice to have a new one in the shop and ready to roll.

352 mm in diameter, 140 mm wide. About 50 pounds. There's always a sigh of relief to find that a new stone has made it across the pond with no damage.

Getting a new silicon carbide wheel is something that only a few guys in the USA would get very amped-up about. Count me in.

The new machine has been doing great work. Lots of terrific feedback from competitors at Sr Nationals this past week, in addition to the great results seen at W. Yellowstone, Bozeman, and Silverstar in December.

IF you're in town for the Methow Valley SuperTour races on Jan 16-17th, then definitely stop in the shop to take a look.


If you're looking for new skis, Ultratune still has a lot of great pairs. Madshus Nanosonic, Atomic "Red Cheetah" World Cup skate & classic skis, and Rossignol Xium WCS. All the new skis are hand-selected, and come with a racing grind and hotbox service included.