Tonttuwerks Stone Grinding

 

"At the end of the day, a stone grind machine is just that. A machine. A tool. Knowing what do with it – when, why, and how to employ its use – that's what matters."

"Grinding a pair of skis is more than simply guiding them over a rotating stone. It's both science and art. A science and art at the center of the mission of Tonttuwerks/Finn Sisu."

*Hand structuring available upon customer request over any of the above grinds. Ask about additional off-menu grinds for narrower ranges and conditions outside the Midwest. Call/email Tom Novak ([email protected]) or come in for recommendations.

**Note—Excessively uneven bases are sometimes impossible to fully grind flat. This can be due to simple wear or some manufacturers design and choice of core materials that have a high susceptibility to thermal damage (i.e. when iron-waxing skis). Tom strives to get skis flat, but it is not always possible—your ski base has only so much polyethylene.

 

The Basics

Tonttuwerks stonegrinding at Finn Sisu ski shop utilizes two Wintersteiger machines. The Omega RS150 and Race NC. On its own, the Omega RS150 is often the main machine in many ski shops offering stonegrinding. It offers digital control and precision with adjustable parameters producing advanced structure designs. At Tonttuwerks it is used to produce quality ski base preparation prior to final grind on the Race NC. The two axis CNC Race NC is Wintersteigers top tier machine – also used by US XC ski Team - with a fully automated process to ensure extremely fine, consistent repeatable custom structures. Having both machines is a significant benefit for our ski shop service operation, especially when catering to competitive skiers, advanced recreational skiers and high-end clients. These machines are state of the art and provide advanced capabilities that can enhance the range of grinding services. These machines enable Tonttuwerks to offer precise race ready tuning. 

Stonegrinding is a specialized 3-part process used to enhance the performance of XC skis by flattening and structuring the ski base. It is performed with a machine equipped with a rotating water-cooled stone that abrasively removes a thin layer of the skis base material. This process rejuvenates the base and creates a specific pattern or texture known as base structure, which optimizes the skis glide in specific snow conditions. Our two Wintersteiger machines each use a specific grit stone – the Omega utilizes a courser grit stone – split with half the surface dressed aggressive for base material removal to flatten, get rid of minor scratches and burnt base and the other half dressed smooth to blank the base, preparing it for the final structure cut using the NC. The Race NC uses a much finer grit stone and specialized diamond cutting bit for the creation of fine precise custom structures. This state of the art two machine approach not only offers the best quality grinds available to High School, club teams, college teams, masters and world cup athletes, it also provides efficiency of operation for the quickest turnaround of stoneground skis. And yes, we can grind skin and fish scale no-wax skis. 

 

In the cold abrasive snow conditions of the upper Midwest, both transformed natural, and man-made, the denser sharper edges of these snow crystals can act like sandpaper on the ski base. This can create micro wear, polishing the ski bases surface. Add in the frequent application of hard glide waxes requiring high ironing temperatures, you can understand that this sealing effect can lead to reducing the ski bases ability to absorb glide wax. Since glide wax penetrates the ski base minimally, typically limited to the outermost surface layer, less than the thickness of a human hair, maintaining the integrity of your base is important. 

 

A performance XC ski base thickness is in the range of 0.5 to 1mm thick. This thin layer is made from ultra high molecular weight polyethylene (UHMWPE) chosen for durability and low friction properties. It's important to note that each stonegrinding session removes a small amount of this base material. While stonegrinding can refresh base structure and enhance performance, excessive grinding will reduce the bases lifespan. Also keep in mind, over time your ski base can swell and warp, becoming uneven. Waiting more than 2 years between stonegrinding a frequently used performance ski can require involved work to flatten the ski base, which will prematurely reduce the ski bases life. I strive to flatten as best I can while still leaving an appropriate amount of base.While there is no one size fits all answer to stonegrinding frequency, seeking professional advice from Tonttuwwerks to evaluate your skis condition - how often you ski, the kinds of snow you encounter and your waxing habits, will help to determine frequency of stonegrinding to balance performance benefits with base longevity.

Details 

XC racing ski bases are made of UHMWPE (ultra-high molecular weight polyethylene) because it provides the optimal combination of durability, glide performance and wax adhesion needed for competitive XC skiing. Cross country racing these days often takes place on abrasive man-made snow or icy tracks. UHMWPE wear resistance ensures the ski base can withstand these harsh conditions without significant degradation. UHMWPE is compatible with stonegrinding. It responds well to waxing, brushing and other tuning techniques making it adaptable for racers who need to fine tune performance. 

 

At a micro level, the areas of the base that glide wax adheres to are called amorphous regions. These are less dense regions in the UHMWPE polymer microstructure. The other more organized denser areas are called the crystalline regions. They give strength to the base while the other gives flexibility. XC racing bases do undergo structural and surface changes after continuous wax ironing cycles and skiing on abrasive man-made snow. These changes can be described as a form of burnishing. When a ski base becomes burnished it can exhibit characteristics similar to waxing glass. This analogy highlights the reduced effectiveness of wax adhesion. Repeated waxing with a hotter iron using harder waxes and the frictional forces from skiing abrasive man-made snow cause some surface level crystalline regions to become smoother. The smoothing reduces surface roughness leading to a polished glossy appearance. Amorphous regions experience compaction under the heat and pressure of waxing as well as the abrasive forces of skiing on man-made snow. Over time these regions may become abnormally dense and become smoother as well as harder. This change can impact wax absorption negatively as the amorphous zones are critical for holding wax. 

 

In addition to flattening and cleaning up burnished ski bases, stonegrinding ski bases imparts a micro level structuring effect that enhances the adhesion of glide wax. This abrasive action creates a series of microscopic pores, ridges and grooves on the ski base. These features increase the surface area enhancing the ability of the base to retain glide wax. UHMWPE is naturally nonabsorbent, so it relies on microstructure and heat to bond with wax. This microstructure tooth provides a mechanical grip for the glide wax (like sanding the kick zone on classic skis to hold kick wax) ensuring better retention during skiing. Stonegrinding is an essential process that creates a micro level tooth on UHMWPE racing ski bases enhancing wax adhesion and overall ski performance. 

 

Thoroughly and consistently cleaning your XC racing ski bases prior to waxing is critical to achieving optimal glide performance and ensuring the durability of the wax. Cleaning removes contaminates, oxidized material and old wax that can interfere with wax adhesion and performance. Dirt debris and pollutants (especially in man-made snow) accumulate on ski bases. If not removed these contaminates reduce glide by creating friction and preventing fresh wax from adhering properly. Clean open structured base material allows fresh wax to penetrate properly and evenly into the base. Modern non-fluorinated high-performance waxes require a clean base to achieve their designed properties. Freshly stoneground bases are cleaned prior to ironed hand waxing or hot boxing to remove grinding residue to ensure proper wax absorption. Incorporate cleaning into your regular ski maintenance routine especially before races or after skiing in dirty snow conditions. 

 

General Waxing Guidelines

Glide wax is crucial for XC skis in cold, abrasive snow whether it’s man-made or transformed natural snow. These conditions create increased friction and base wear which makes proper waxing essential for the speed, durability, and race performance of your skis. This snow type has larger, sharper ice crystals that aggressively scrape ski bases. This rough snow creates higher drag slowing skiing significantly. The sharp crystals strip wax faster than soft, powdery snow which requires specific hard waxes and frequent reapplication to protect your ski bases. Without wax, skis ‘stick’ to the rough snow, shortening your glide distance and increasing your effort per stride. 

Regular waxing prevents the base from becoming scratched, oxidized or burned over time. (Oxidized in this context refers to the ski base drying out and the degradation of the UHMWPE surface, rather than chemical oxidation. This drying leads to reduced glide and diminished wax adhesion.) Learn to reapply glide wax when you notice skis slowing down significantly and if the bases look dry with white patches, especially after 10 – 30km of use. When skiing on cold abrasive man-made snow, you can generally expect basic hard wax to last 10 – 30km, while high performance waxes and proper layering can extend that range to 15 – 50km. In transformed, natural snow you can expect wax to last up to 50km. Regular waxing before every race and long training sessions ensures consistent performance. 

 

Wax Application Steps

1. Drip the wax of the day evenly on to your ski base. Make sure there is enough to spread on the entire ski base to help insulate the base from burns.
2. Spread the wax out with a brief pass of the iron.
3. From tip to tail, make a pass with the wax iron set to the proper temperature for the wax being used. You can find the temperature printed on the wax's box or often on the wax company's website.

IMPORTANT - let your skis cool every time you pass with the iron before putting your iron back on the ski. Otherwise, just set them aside after a pass and work on your other ski.

Proper Iron Technique

When you're making a pass down your ski with an iron, you will often see a trail of liquefied wax. For harder waxes like Optiwax's Ceramic paraffin and Star Polar, you want to keep the trail no longer than an inch behind the iron. For your classic blue gliders and softer waxes, you should see 2-4 inches of liquefied wax.

You will need to speed up on the thinner parts of your ski and slow down in the center. Each pass of the iron will see you speeding up, slowing down, and speeding up again. If the trail ever gets too long, speed up!!