Posted on 4th Sep 2011 @ 9:31 PM
As a ski or snowboard slides over snow crystals, heat is created due to friction. This heat, in turn, creates water droplets by melting the tips of the snow crystals. Water is the key to bases that are fast and easier to turn, but only if the correct amount is present under your skis or snowboard. If the snow and humidity is very dry, there may not be enough water present to help improve glide. In this case, it may need to be produced through greater friction between the snow and a base with a smooth or fine structured finish.
When snow is warm or wet, however, excess water can be generated underfoot that creates suction and slows your glide. In this situation, the base should be structured with a pattern, which, similar to tire tread, breaks up suction and helps channel water away. In general, a finer structure with base rills or ridges spaced .5mm or less apart is best for cold, dry snow...and a coarser structure with base rills or ridges spaced .75mm or more apart is best for warmer wet snow.
Another rule of thumb is that the rills or ridges should never be larger than one-half the size of the snow crystals...this avoids crystals from getting stuck in the troughs of the structure and creating drag.
Structuring can make more difference in speed than waxing, according to world cup technicians. It can also make a board or ski easier to turn for recreational riders. Electra (black) bases don't need as deep a structure as a clear sintered base since they develop less heat overall...and fluorocarbon waxes also work well with a finer structure due to their greater water repellancy.
The structure imparted at most ski factories tends to be a medium-to-coarse pattern. While this may be appropriate for wet snows commonly encountered in the Sierras and Cascades of the far west, it sometimes proves too aggressive for colder Wasatch and Rocky Mountain snowpacks…where drier, smaller and sharper snow crystals can lodge within the recesses of these coarser structures. This can create greater drag and turning resistance...neither of which you’ll want on...especially on a race course.
For best results, check with a knowledgeable race shop to find out what race structures work best in your personal race arena.
You can change this by hand structuring at home or going to a good shop for a stonegrind. After any structuring, always inspect the base before waxing...look carefully for small p-tex hairs or microhairs. If present, they must be removed (use scotchbrite pads followed by omni-prep pads) or your base will be slower than before.
CHOOSING A STRUCTURE PATTERN
There are a variety of structure patterns. Linear structures are straight grooves that run from tip to tail. Most hand-produced and belt-sander structures are linear, which works well for a wide variety of conditions, and is excellent for Super G and downhill races. Broken linear patterns are shorter random structure lines that also run straight from tip to tail. Cross-hatch or diagonal structures are produced on a stone grinder by passing a diamond dressing tool in intersecting patterns over the stone face, and has traditionally been preferred for slalom and Giant slalon races.
Structure patterns and preferences sometimes change depending on many factors...weather and snow conditions, the whims of individual technicians, new structure tools, etc. Combination structures are commonly tried as well...such as a linear pattern overlaid with a light cross-hatch pattern, or a light linear pattern overlaid on a coarse linear pattern, etc. It's not a science carved in stone...only p-tex...so it's subject to change. And there' re more variables one can consider when choosing structure...such as the type and speed and length of the race, the type of base material involved, the color of the ski or board (which affects how much heat it'll absorb on a sunny day), the core material involved (steel, wood, foam, sagebrush?) etc. Then regardless of the pattern used, you can debate the depth of the structure, configuration of the channels (peaked or planed-off ridge tops? sharp or semi-filled troughs?), spacing between channels, random or uniform width rills, etc. Obviously there's enough rocket science here to keep anyone occupied.
Being basically lazy and cheap, we use hand tools to impart a basic linear pattern unless it's a special event that merits a spendy stone grinding. We generally use a fine-medium pattern for cold, early winter, snow and a coarser one in late winter and spring when temperatures warm up. And we use the same basic linear pattern on all of our gear... including nordic skating and diagonal-glide skis, tele and alpine gear, freestyle and racing snowboards (and, of course, on plastic trays for those exciting fast-food races).
Several years ago, the Norwegian Nordic Ski Federation revealed that a crosshatch structure, while good on wet snow over 25 degrees F, attracted more dirt after 5km than a linear structure in dry snow conditions. They also recommend only using very fine structure for new or old snow conditions when the air temperature is below 5°F (-15°C)...and also when skiing on old or transformed fine-grained, hard-packed snow at temperatures between 20 & 32°F (-7° & 0°C) in dry air and low humidity.
STRUCTURING WIDE SKIS & SNOWBOARDS
It's more important than ever to structure the bases of shaped or powder skis as well as snowboards because their wide forebodies tend to "plow" more snow and have to overcome greater amounts of friction and suction in order to glide well.
The higher speeds of racing normally benefit from a coarser base structure than recreational gear needs, but be careful about too coarse a structure...excessively deep structures can affect guidance, making alpine skis or snowboards more difficult to turn. Conversely, a deep structure can enhance the tracking performance of a nordic race ski, where straight tracking is often desirable.
Base structure on alpine race snowboards can improve a rider's time by 2-4 seconds in a 90 second downhill race. But don't structure too heavily...too deep a pattern can inhibit turning ease.
CUTTING VS. PRESSING IN A BASE STRUCTURE
Different tools create base structure in different ways. For example, tools like the brass riller bar create structure by pressing or imprinting it into p-tex base material...whereas the SkiVisions base flattener/structure tool or skyver tool create it by cutting away p-tex. Theoretically, a brass riller bar can also be used to cut, although we recommend it only be used to press in a structure because, unless brand new, it doesn't cut cleanly or easily.
In general, pressing in a structure is less durable than cutting it in. This is because p-tex is fairly elastic material, which...when exposed to heat (such as when hot-waxing)...tends to return to its original shape and condition. This occurs on extruded bases at temperatures above 210 degrees F (99 degrees C) and on sintered bases above 270 degrees F (132 degrees C). A pressed-in structure, therefore, will become shallower and less defined fairly quickly if you hot-wax frequently.
A structure that has been cut into p-tex doesn't suffer this same problem as readily...but you need to make sure that structure tools are kept sharp. This means sharpening or replacing blades on the SkiVisions base flattener regularly, or replacing the Swix steel brush after every 7-8 pair of skis or so...otherwise they tend to rip and tear out p-tex instead of cutting cleanly. Ripping and tearing creates a ton more of unwanted p-tex hairs or fuzz...which will take even more time to remove afterwards.
Another significant advantage of using a structure tool that cuts is that it removes oxidized p-tex on the surface of the base in the process. This helps the p-tex to absorb more wax.
All base structures wear down in time and occasionally need to be renewed...how long this takes depends on the snow hardness, frequency of waxing, base material hardness, how often you ski or ride, etc. Check it visually on a regular basis, or lightly run a fingernail across the base to feel the structure. You may also want to change structure during the season...from fine to coarse as the season changes from cold winter to warm spring.
BRASS RILLER BAR
Swix recommends using the coarse teeth on a brass riller bar on your first pass down a base when structuring, followed by a second pass using the fine teeth. Follow this with a few light passes with a sharp steel scraper, then rub with a scotchbrite pad followed by an omni-prep pad to remove any p-tex fuzz or hairs.
BETTER GRIP ON RILLER BAR
When structuring nordic racing ski bases, I clamp a small c-clamp on one side of my brass riller bar...it helps grip the bar and serves as a guide along one edge to help keep your structure pattern going straight down the ski from tip to tail.
-Ron Macleod, Salt Lake City, UT
STRUCTURE TOOL QUESTION
I’m hoping someone at Tognar can help me. I purchased the SkiVisions Ski Structure & Skyver Tool late last season. I have tried to use this device to put a good structure on my skis, but so far my results have been horrible. According to the description of this tool I was supposed to receive 5 steel blades with both fine and coarse cutting structures. As far as I can tell, all of my blades impart the exact same pattern with the exact same depth on my skis – and this pattern is unusable. The steel blades all create a pattern where it leaves fairly thick “grooves” each about ¼” apart. I’ve never seen any ski structures that look like this. The grooves are way too far apart. I’m used to my brass riller bar that leaves a very nice uniform closely spaced linear pattern. The steels blades leave marks on my skis that look like I ran over a rock garden – not a nice structure.
Am I doing something wrong? Did I get defective blades? As it stands now, I think this tool is useless for me unless there are replacement blades that leave shallower smaller grooves that provide more closely spaced “tracks” (less than 1/16 of an inch at least).
Jack At Tognar Toolworks has asked me to respond to your email. Forgive me, but I am going to have some fun with this response. Making tools at SkiVisions is a lonely business, so you have "opened the box" for a response.
Let me open with this comment, I only make tools that I want to use. If the tools are available in the market place that I want, I buy. When they aren't, I make. I have no interest in going toe to toe with other manufacturers over small variations in design to create sales. That is why my SkiVisions tools don't look or perform like any other tools available. People may or may not like them, but nobody ever argues with their uniqueness. Bottom line, if you want conventional, look elsewhere.
Structure tools are difficult to understand because their performance really cannot be analyzed scientifically. Therefore we are stuck with concepts of designs and expectations of results. Most of us use the 'uphill skate' testing method to analyze structure and wax. To do this, you simply skate uphill. It is a "feel" experience, not capable of mechanical analysis. But, when you get good at it, it really does work. Wax and structure interpretations vary from awful to wow. With lots of variations in between. One thing that is clear though, when my skis are "wow", I rip. Plain and simple. Getting good at the skate uphill method of analysis can get you there. It really is worth the time and effort.
I used the riller bar probably 25 plus years ago. I used to attach a zip tie and drag it along the ski edge to give a perfect structure pattern ( with a small change caused by the side-cut). It looked great. I just didn't like how it skied.
Shortly thereafter I developed the stone blades for the Base Flattener which performed far better and never used it again.
Why do I think it doesn't work very well? Two reasons. First, the purpose of structure is to reduce surface tension (suction). Structure accomplishes that result by giving pockets or channels in the base for air to "hide" in, the air then prevents suction tension from forming. However, the shallow angles imparted by the riller bar don't leave any place for air to hide, the valleys easily fill with snow. Second, the tool imparts a constant peak and valley structure which I believe creates drag. Flat surfaces are far better for speed, but they naturally produce surface tension. The riller bar ignores that reality.
The Base Flattener stone blades are better than the riller bar because they cause a generally flat surface but what is particularly important about them is that they open the pores of sintered bases far more effectively than stone grinding, the pores then help to provide the "hidden pockets of air" to reduce surface tension. The pressure and speed of a stone grinding wheel moves base plastic laterally, closing off pores as it grinds off plastic. Although stone grinding can make bases look great, I really think the result have significant limitations.
Even though the stone blades worked very well, I still wasn't satisfied with what I really wanted. My objective, to maximize structure benefit, was to have lots of flat base area that is cut extremely cleanly so that the base pores are left wide open, and, deep and very narrow structure cuts to give lots of area for air to "hide" without having significant affect on the flat base surface. It was incredibly difficult to find a way to achieve that result, but the structure tool does just that. Regardless of its athletic interpretation, it is a very effective device.
Now, to your comments and objections.
You cannot observe the structure it imparts by looking at the ski bases. Your objection questions the very objective I was trying to accomplish, various levels of deep structure that are not observable on the surface. You can see the depths of the structure by looking at the blades, but you really can't see it by looking at the base. I think that is the way it should be and worked hard to get that result.
The distance between each tooth is 3/16 of an inch. Each additional pass down the ski will make that distance change, obviously. The number of passes is the choice of the tuner, the desired results are personal. We give you tools that allow you to experiment effectively and find what you want, but the final choices are yours. With ski tuning, there really isn't any right or wrong, it really is personal. I don't tell anyone how I tune my skis because it would be considered "wacko". But it works for me, it is very creative, and very unconventional. And fun.
Each blade has two cutting edges, the serrated edge and the "smoothe" edge. If you feel it carefully you will feel a burr on the smoothe edge even though the edge looks harmless. That burr is sharp and will cut base plastic effectively, it is what I call the "fine" blade but maybe it should be "extra" fine. The point is this, after you structure with the serrated side, it is good tuning procedure to go over it with the "fine" blade to finish the job.
I have to admit that I am continually reluctant to introduce tools and tuning concepts because they conflict with conventional approaches. The structure tool is a perfect example. What can I say. I think the tool incorporates objectives that the competition hasn't even begun to think about. Those are my thoughts anyway.
- Mark Sewell, SkiVisions
After structuring, make a few light passes with a sharp steel scraper (or similar) from tip to tail down the ski base. This removes any sharp ridgetops that might otherwise protrude too deep into the snow and reduce glide.
STRUCTURE SANDING CHART
Here's a chart for determining what grit to use if you structure your skis with silicon carbide paper...
Snow Temperature Grit
-4°F (-20°C) 320
3°F (-16°C) 240
7°F ( -14°C) 180
14°F (-10°C) 150
25°F & above ( - 4°C) 100
Always use a sanding block when structuring a ski base with silicon carbide paper and work bases from tip to tail using smooth, even, overlapping strokes. Follow up using a scotchbrite pad wrapped around a sanding block or with a twist-lok block to remove loose P-tex hairs that were created during the sanding process.
-Terry Young, Aspen, CO
After structuring, make sure you examine the bases from the side while you remove the p-tex hairs. What looks clean from the top can look very fuzzy from the side. This is especially true if you structure with regular sandpaper.
-Scott Irving, Cape Elizabeth, ME
FAST OLD BASES
Many racers think that frequent stone-grinding is the key to fast skis...but this may not be true. On the World Cup, race skis are rarely stoneground...sometimes only once at the beginning of a season. Instead, they are well-waxed and brushed with a special steel bristle brush on a regular basis. Although the structure slowly wears, the microscopic surface of the base becomes increasingly smoother and faster over time.
NORDIC SKI STONEGRINDING
One benefit of stone-grinding bases is that the structure can be exactly reproduced time and time again...a good deal if you find a particularly fast structure for a specific snow condition. But there's a few concerns you might want to be aware of, too. First, it takes about 5 or 6 passes over a stone grinder to get ski bases flat, followed by 3 or 4 more passes to put in the structure. That's a lot of grinding. On alpine skis or snowboards that have steel edges and thick p-tex bases, this is no big deal...you have lots of material to work with. But nordic skis obviously don't have steel edges, and the base material is often much thinner, too. If too much material is removed each stone-grinding, you may not have much of a base left to stand on...literally.
There are big differences between stone grinding alpine skis and nordic skis that shop mechanics must understand... using the right binding bridge, the speed that the ski passes through the machine, the pressure that's applied, the dramatic flex and camber of a nordic ski, and the narrowness of the ski...wider alpine skis are well supported by ribs on the feed wheel, whereas nordic skis can easily rock side-to-side on these same ribs, causing severe base damage. It's also thought by some technicians that the flex of a nordic ski is affected by the thickness of the base material...so the more base you grind off, the softer the flex becomes. And, lastly, the high price of stone-grinding adds up quickly.
Our advice? If you're getting a stone grind, seek out a shop that specializes in nordic ski machine tuning and has the expertise to do it right...you may get up to 10 grinds from your skis before they're toast (versus only 1 or 2 from the shop down the street). Otherwise, stick to hand structuring where you can completely control the process.
Nowadays, the tops on many skis aren't flat...they sport structural ridges, rails, ribs and other features. Although they may look cool and contribute to ski performance, these features can cause big problems when running 'em through a stone grinder. The top feed wheel on most stone grinders will firmly push down with greater pressure on high spots and less pressure on lower spots... resulting in anything but a flat base after grinding. This can really screw up a ski, so if you're taking your gear in for a stone grind, be sure the ski shop is aware of this potential problem. Some shops will use plates or dense foam that attach to the ski tops to help neutralize these irregularities, others make light slow passes to minimize ski deformation, and some fancy robotic stone grinders use full-length, constant height transports to apply even pressure along the length of the ski. In any event, be sure the shop frequently monitors base grinding progress with a true bar to avoid potentially damaging results.
SAVING A STONEGROUND STRUCTURE
I put a small but noticeable gouge in my base that needs repair, but I don't want to disturb the nice factory stoneground structure on my base. How can I do that?
Also, I have a similar problem with oxidation on my bases sometimes...how do I remove that without diminishing the existing stoneground structure?
First off, Sean, if the base gouge is small, repair it using a base repair iron or drip candle if it's shallow. Either of these methods allow you to fill a gouge without impacting much surrounding base material. Then let the p-tex cool and remove any excess with a versaplane blade, followed by a sharp steel scraper. These steps, if done carefully, allow you to complete the repair without affecting much surrounding structure. And since the repair is so small, it's okay to leave this part unstructured since it's probably too small to have a noticeable effect on your glide.
Oxidation, however, is a tougher challenge since it usually involves a larger surface area. First, we would recommend hot-waxing on a regular basis to help prevent oxidation in the first place...this is the cheapest and easiest way to avoid it. Baring that, we'd recommend making light passes over the oxidized area with a fine scotchbrite pad, followed by more light passes with an omni-prep pad, followed by brushing the structure with our steel base texturing brush. If this does the trick, it should also leave most of your original structure intact.
If the oxidation is deeper, however, you'll need to sacrifice some structure. Use the Skivisions Base Flattener tool or a sharp and stiff steel base planer blade to scrape away the offending area. Follow this work with the steps listed above. Then you'll need to renew the structure by getting a new stonegrind, or imparting a hand structure. Afterwards, hot-wax the base on a frequent basis to help protect it from future oxidation.
The ski-tuning machinery used in ski shops is only as good as the nut on the end of the handle. Sophisticated stonegrinders and other tuning machinery isn't necessarily difficult to operate, but can do an awful lot of damage when run by someone who doesn't know what they're doing.
-Jim Deines, Precision Skis, Frisco, CO
STONEGRINDS BY MAIL
If you can't get the quality stonegrind you crave locally, here're some shops you can send your skis to for quality work. Call them for details and rates:
Precision Ski, Frisco, CO Call (970) 668-3095, ask for Jim Deines
A Racers Edge, Breckenridge, CO Call (970) 453-0995, ask for Greg Guras
Rossignol Skis, Williston, VT Call (802) 863-2511, ask for Jim Fredericks
Precision Ski, Frisco, CO Call (970) 668-3095, ask for Jim Deines
For some events, race techs will stonegrind the front half of a ski base with a crosshatch structure (they claim it provides faster acceleration), and the back half with a linear structure (for faster top end speed).
SHIVER ME TIMBERS
According to science books, dynamic friction (between moving objects) is always less than static friction (between objects that are at rest in respect to each other). Does this mean that vibrators will soon be inserted into race skis and snowboards for quicker acceleration?
WORLD CUP TIP
Know your skis, your bases (cold or warm bases), and your structures. Keep track of snow temperatures, humidity and snow crystals, as well as which skis ran, and where and when they ran. Important factors often overlooked are the time of year (November or April), time of day (shady or sunny), and what condition the snow is in when the race goes (1st or 60th). Also make notes on the skis that didn't go and why...put all the information on record.
-Curtis Bacca, Salomon Serviceman for Kyle Rasmussen
Speed skiing champion Jeff Hamilton usually got 10 to 12 runs down a speed ski course (at speeds up to 150mph) before he had to restructure and wax his 240cm Dynamic skis.
Windblown snow is up to 4 times denser than snow that falls in calm weather. Because they are smaller and rounder than normal snow crystals, there is more surface contact between the ski and snow, thereby increasing friction and heat. This results in more snow crystal melting and therefore more free water. It would stand to reason that you should structure the base coarser and use a warmer (more hydrophobic) wax to accommodate these conditions.
Some folks think p-tex bases contract in cold weather, pulling the edges closer together to create not only a concave base, but a loss of base bevel as well. Ex-Aspen techmeister Terry Young says he agrees that this certainly was a problem with skis made 5-10 years ago...so much so, in fact, that he installed a freezer in his ski shop where he could cool skis down to -20°F before base grinding and tuning them. This super-cooling resolved any contraction problems when tuning, plus the cold p-tex cut cleaner when sanding or grinding bases. Terry feels that today's skis are constructed and factory finished better, and it's no longer necessary to use this 'freeze-tuning" technique.
SIZE DOES MATTER?
One theory has it that the structure on a base should be such that the rills are one-half the width of the snow crystals you'll be on. This prevents crystals from getting "lodged" in the structure and creating drag. Use wax to change a deep structure to a finer structure by not brushing as agressively after waxing...it leaves shallower rills. Plastic bread wrappers are handy for binding storage or to put between ski bases after tuning. If you ever use a belt sander on bases, try sponging the bases with water to keep them cooler.
-Chip Filbry, Ventura, CA
P-TEX HAIR REMOVAL
Here's a trick for removing excess p-tex hairs created while base sanding or structuring...iron on a layer of Swix Extreme wax additive just enough to melt the wax but not heat up the base. Then take the ski outside to rapidly cool it. This makes the wax brittle. Scrape the ski and the p-tex hairs will "pop" off with the wax.
NORDIC SKI BASES
Getting nordic ski bases to glide faster is the perpetual quest of any serious tuner or racer. One key to this is thoroughly removing microscopic p-tex fuzz or hairs on your p-tex base. This is not as simple as many think.
After structuring (whether by hand or stonegrinder) there are literally thousands of polyethylene hairs left attached to a p-tex base. To remove these, the base first needs to be lightly scraped with a sharp metal scraper (a shaving blade scraper is ideal for this). Next, rub the base with a fine scotchbrite or fibertex pad backed b a rigid scotchbrite holder or sanding block to ensure even pressure is applied across the full width of the base.
But now, even after both these steps are taken, there will still be lots of very short, stubby, p-tex hairs left on the base...sort of like a crew cut. Whaddaya do?
Ski 'em off! According to the Fischer nordic tech team, the Italians hire people to ski 30-40km until the bases ski fast. The Norwegians do the same, but feel it takes more than 30-40km. In any event, the snow abrades away the p-tex hair and the skis get faster.
At the nordic World Cup level, base structure has generally become finer and less aggressive than in the past due to the widespread use of fluorocarbon waxes...which are more hydrophobic and release the surface tension of water better. But if you don't use fluoro wax on a regular basis, then you're better off sticking with a more aggressive structure on your nordic skis.
There may be a trend among nordic racers to return to clear p-tex bases. Why? Theoretically, it can absorb up to 15% more wax than a graphite base. At the Thunder Bay World Championships a year and a half ago, there were a number of clear bases used.
Ironically, five years ago, most nordic race skis had clear bases, then everyone switched over to graphite. Now, with the widespread use of fluoro wax, it looks like racers may return to clear bases again.
-Ski Research Group at Eagle River Nordic
Sometimes, when on the road, we end up with skis prepared with a base structure that's too deep. A quick fix is to wrap 220 grit (or similar) silicon carbide paper around a flat file and take a couple of passes down the ski, then re-wax. You'll find most problems caused by the deep structure will be corrected. Just be sure to use a very flat file.
-Tiger Shaw, Former Volkl Service Tech
MORE SPEED QUICKLY
In the past, many race skis seemed to take a whole season of prepping before they got really fast. But with some new preparation techniques, skis can be made to get faster quicker. This was demonstrated recently when a nordic world champion race was won by Bjorn Daehlie on new skis fresh from the factory, followed by a little preparation. Although this occurred on nordic skis, the same procedure would likely prove true on alpine skis and snowboards as well since they all use similar (p-tex) base material. Here's a summary of what steps were taken. First, the skis were stoneground the day before the race by a world-class nordic technician...followed by rubbing with an omniprep pad. Then they were waxed, plastic scraped, and brushed 25 times with a soft high-fluoro wax, before applying many layers of the wax of the day. In testing, these new skis proved faster than any of Bjorn's older race skis.
Not all of us, of course, have access to world-class stonegrinding or unlimited supplies of high-fluoro wax! But the use of omniprep pads to remove p-tex fuzz (microhairs on a base) after fibertexing can probably help improve glide significantly on almost anyone's skis or boards after stonegrinding. And the repeated application of wax to a base (the best quality you can afford) followed by scraping and brushing cannot be overemphasized. Granted, rarely can we afford the time or wax to make 25 applications of wax...but if possible, make at least three, and wait thirty minutes or so before scraping each time. In test after test, and race after race, it has been proven that frequently waxed bases will outperform those less frequently waxed.
When possible avoid sliding over "Load Here" boards in chairlift loading areas that can scrape wax and structure off bases. Lift operators may growl, but your boards won't!