Kuzmin scraping and structure

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MN Hoser
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Re: Kuzmin scraping and structure

Postby MN Hoser » Fri Mar 29, 2013 3:21 pm

I think the reason for matching wax hardness is what the Germans call "sacrificial lubrication." That is, when a sharp crystal hits the wax, it flakes off a molecule of waxrather than breaking the crystal. I don't know much about it, except harder than optimum wax is slightly slower. Softer than optimum wax is really slow.

Now in pure fluoros, it seems the deal is different. SkiGo C22 melts at a very high temp, and it seems (don't know) that it's therefore a hard wax, presumably to resist dirt. Sometimes C22 works well at cold temps and sometimes it doesn't.

Go figure.

Jay

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Re: Kuzmin scraping and structure

Postby MN Hoser » Fri Mar 29, 2013 3:24 pm

I guess I should say that SkiGo is intended for wet conditions. (Great wax for that.)

Jay

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Re: Kuzmin scraping and structure

Postby osloskier » Sun Mar 31, 2013 5:56 pm

Loran wrote:The only drawback is that PTFE is slightly heavier.


PTFE has one more, unfortunately very large, drawback. PE is five times more abrasion resistant than PTFE.

MN Hoser wrote:I think the reason for matching wax hardness is what the Germans call "sacrificial lubrication." That is, when a sharp crystal hits the wax, it flakes off a molecule of waxrather than breaking the crystal.


The problem with that idea is that there isn't enough wax underneath the ski to keep doing this for more than a few tens of meters. By definition the wax is lost in this process, and the wax layer is very, very thin.

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Re: Kuzmin scraping and structure

Postby Loran » Mon Apr 01, 2013 3:49 pm

osloskier wrote:PTFE has one more, unfortunately very large, drawback. PE is five times more abrasion resistant than PTFE.


Yes, but that doesn't mean that it's not resistant enough for most conditions.
And cross-linked PTFE is more abrasion resistant than PTFE.
Note that I'm just quoting Kuzmin Phd thesis by mentionning all this.

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Re: Kuzmin scraping and structure

Postby MN Hoser » Mon Apr 01, 2013 8:10 pm

osloskier wrote:The problem with that idea is that there isn't enough wax underneath the ski to keep doing this for more than a few tens of meters. By definition the wax is lost in this process, and the wax layer is very, very thin.


Why do you say that? When you cork on pure fluoros, it's generally accepted that it's faster than ironed, but it doesn't last. The numbers tossed around about how long a corked layer lasts is 10 km or 20 km, not 10 or 20 meters.

Jay

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Re: Kuzmin scraping and structure

Postby osloskier » Thu Apr 04, 2013 1:38 pm

MN Hoser wrote:
Why do you say that? When you cork on pure fluoros, it's generally accepted that it's faster than ironed, but it doesn't last. The numbers tossed around about how long a corked layer lasts is 10 km or 20 km, not 10 or 20 meters.

Jay


What I meant was that the contribution to improved glide from sacrificial lubrication can't be large, because that sort of lubrication would use up the wax in the process. So if that process contributes significantly, then the wax would very quickly wear off. Whatever it is that the wax does, it has to be something else, at least primarily.

Fluoro works by increasing hydrophobicity, so that's a different process.

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Re: Kuzmin scraping and structure

Postby MN Hoser » Fri Apr 05, 2013 2:03 pm

What I'm saying is that you can't make a "hand wave" statement (in this case, saying the wax would wear off too quickly) without data to support that statement. There is data out there where wax techs put a coat of rub-on fluoro over an ironed flouro to speed up the ski for a number of km. The speed improvement is most at first and then decreases. The interpretation that sacrificial lubrication is contributing to the speed may not be correct, but it fits the data. Your statement that it would wear off to quickly...well, where's the data?

The alpine guys put Cera on their skis and hardly cork it in. They simply want some extra speed to get out of the gate. So the "wearing" depends on how the material is applied. In that context I would agree with you that the wax would wear too quickly.

BTW, the sacrificial lubrication term came from a conversation I had with a chemist from Cerax (remember that?). The coatings like Cerax can produce a highly hydrophobic surface, but it can't have properties sacrificial lubrication. (The coating is one molecule thick.)

Jay

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Re: Kuzmin scraping and structure

Postby osloskier » Tue Apr 09, 2013 2:19 am

I don't have any data on that, unfortunately, and a lack of data seems to be a common theme in every discussion on ski glide ;)

The wax is the same material whether it's in a block or underneath a ski, so if sacrificial lubrication was a significant glide mechanism, then a block of glide wax should glide well on snow. It doesn't. It should also feel slick, like for instance graphite powder does, but it doesn't do that either. Also, one would think more wax would be better, but not scraping and brushing yields very poor glide.

I tried to do some calculations on the number of wax molecules vs snow crystal collisions, but it quickly becomes completely meaningless, because I have no clue how many wax molecules would be required to lubricate a single snow crystal, how many snow crystals actually contact the ski, etc etc. What I can say is that if 1 mg of wax remains on the ski base per square cm (which is on the order of the numbers I've seen), then the wax layer is about 1/100 mm thick on average. Most of that will be in the valleys and not on the peaks. It seems extremely unlikely to me that such a small quantity can contribute to glide by any measurable amount through sacrificial lubrication, but I can't prove it. In addition to that is the fact that cold wax is really quite hard and doesn't seem to have anything like the consistency I would expect from such a lubricant.

But you're right, it's all just handwaving.

I personally think the wax works just like spackling paste, by smoothing out unevenness, embedding fibers and filling in holes. I'm guessing there's also an element of Brazilian waxing to it - the wax embeds the fibers, and when scraped off, the fibers are torn off too.

This would make the snow crystals less likely to find anything to snag on, and the water droplets less likely to find something to adhere to, and seems logical and reasonable to me. In contrast, I can't wrap my mind around how a rather hard substance would be able to sweat out of a cold ski base and provide any useful lubrication, or how that same not all that slick substance would suddenly turn into a great lubricant when applied to a ski.

If PE is able to dissolve a small amount of wax, which according to a plastics expert who sometimes posts on the Swedish XC forum is actually possible (note, this does not involve any pores), then there is a possibility that this might affect the hardness of the ski base. That should be possible to measure, but I don't have the equipment to do it. If this is the case, then that would be another mechanism that I would be able to understand.

Fluoro is a different matter, that stuff is more hydrophobic than PE and thus able to make the water droplets more round and less sticky. I have no experience with it, so I can't even speculate.

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Re: Kuzmin scraping and structure

Postby MN Hoser » Tue Apr 09, 2013 5:24 pm

I admit that it seems improbable that wax could provide lubrication. I'm primarily referring to a pure fluoro rub on that is corked and not "regular" waxes that are ironed. If you do the numbers thing, yup, it doesn't seem to make sense. Einstein said to a guy that (using math) thought the universe expansion was increasing, said something like "You math is good, but your understanding of physics is terrible." Einstein thought that obviously, the universe expansion has to slow because of gravity.

Anyway, I used to rep Cerax. On a ski in wet conditions, I didn't brush my skis as well as normal. (Normally I'd rotobrush the skis really well.) I noticed the skis started fairly fast and slowed pretty quickly....as in 400 meters later. The next time skiing, I applied Cerax and didn't brush at all. That means there was a white residue of material left on the ski. (Cerax was a suspension in an alcohol base that after application, would evaporate.) The ski had kind of a haze over the base. As for amount of material left on the ski, it's hard to imagine more than 0.1 g being on the ski and most likely less. I was skiing in very wet, slushy conditions, and the skis were incredibly fast when I started skiing and continuously slowed to very slow (normal for really wet conditions) in about 700-800 meters. It was the end of the season ski with big puddles. (As I remember anyway. :lol: ) So the skis went from about as fast as a ski can be to really slow like you'd expect when skiing through slush.

That day kind of blew my mind. I kept thinking about ways to use that advantage in races. (At the time, there was no sprint racing.) Again, how do you rationalize that this film of material would speed up the ski, and if it's wearing off, how could there be enough material there to do that? Why would the stuff wearing off help in wet condtions?

What I've experienced with pure fluoro rub ons is the similar except 100x or 1000x less effect. That is, the skis are slightly faster at the start and slow gradually.

Jay

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Re: Kuzmin scraping and structure

Postby osloskier » Fri Apr 12, 2013 3:45 pm

Weird and interesting stuff. I think sacrificial lubrication seems much more likely to be happening in the case you're describing than with regular wax.

Today I again experienced just how enormously different the conditions can be from one day to the next. Sometimes I completely misjudge the conditions up in the forest, just ten minutes away from my house.

Two days ago the snow was mostly coarse grained, somewhat wet, but fairly firm, and I had quite good glide. Today it was almost like mashed potatoes and the glide was horrible. I used my very "warm" nanosonics with Kuzmin U structure in both cases. I know for sure that my other skis would have been even worse, but even so I was double poling downhill. I'll rescrape them with the + scraper and try again and see what happens.

I've ordered a lens reversing coupling ring for my camera so I can take a really close look at the ski bases.

A guy called Björn has performed many dozens of tests of Kuzmin scraped vs waxed skis in the ski tunnel in Torsby (The ski tunnel: http://www.skitunnel.se/omoss/skidtunnelfakta.50.html). About 30 pairs of skis have been tested. The first post has been continuously edited to include new results, until it got too large, so there is another summary post at page 6. Take a look, try Google Translate. Here are some words that it stumbles on: stavtag = pole stroke, sicklat = scraped, vallat = waxed, nyvallat = newly waxed, fischervallare = fischer waxer (not fischer robbers!). I can translate if something is indecipherable.

http://www.skidforum.se/viewtopic.php?id=4913&p=1

Translated: http://translate.google.com/translate?s ... 13%26p%3D1

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Re: Kuzmin scraping and structure

Postby osloskier » Mon Apr 15, 2013 2:11 am

April 13. I rescraped to the + structure and added a 1 mm linear rilling. That didn't help any, it was just too wet.

April 14. I re-rilled with both 1 mm linear and two passes with a tractor tire riller, pressing down hard. The result was stunning. The rain started as a drizzle and increased until I had to wring the water out of my buff. The snow was even wetter than on the 13., but I actually had very good glide. I thought maybe the snow had firmed up a little, but then I met a guy who immediately switched from V2A to V1 as he reached the bottom of the hill he was going down. He had no glide at all. His face had the color of a tomato and he didn't look happy, in fact, he looked like he might keel over at any moment. But then, V1 in flat terrain isn't all that much fun. I whizzed by at twice his speed in an easy V2A.

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Re: Kuzmin scraping and structure

Postby Loran » Wed Apr 17, 2013 4:56 am

For spring wet old snow, I dedicated a pair of stiff skis.
Kuzmin+ scrapper, 1mm and 2mm Swix riller, Toko roller medium and coarse.

Having tested different skis with the same or lighter treatment, I can tell that the more important factor is, as usual, the ski.
More precisely, in that case ski with short contact areas but not too stiff because too stiff won't go well in slush.

The best pair is my girlfriend's old Xium F3. Even though F3 was the softer in range at that time, it's still very stiff to what we find today and they have the shortest contact areas of all skis I have around.
Weighted with 65 Kg, the front contact length is ~28cm and the rear contact area is ~49cm.

I finally bought the Telfon Brush. I didn't make glide comparison but skis stayed very clean over the last 150 km.

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Re: Kuzmin scraping and structure

Postby Loran » Mon Oct 28, 2013 4:00 am

Hi,

I have compiled a few pages about the "no glide wax" approach. http://simplyglide.wordpress.com/

Forgive my English and don't hesitate to correct me if my English is wrong. I did it for French skiers first, as there was a lack of information on this in French.
I did translate it in English as anyone might be interested to have a summary on it.

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Re: Kuzmin scraping and structure

Postby sandatos » Fri Nov 15, 2013 7:08 am

Hello,
I just read some topics on Kuzmin scrappers and also the thesis of Giesbrecht (polymers on snow, toward skiing faster)
http://www.polytech.mat.ethz.ch/researc ... brecht.pdf

So from what I understand the most important thing to get fast ski is to adapt the structure of the ski to the structure of the snow so that both have an equal roughness.
It would imply to always change the grinding of the ski sole with changing snow.

With Kuzmin prep skis, do you change the sole structure by flattening the sole with the drum and then use a various rillers and brushing ? I think always using the kuzmin scrapper will wear out the sole quite fast ?

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Re: Kuzmin scraping and structure

Postby Loran » Sat Nov 16, 2013 4:31 am

sandatos wrote:
With Kuzmin prep skis, do you change the sole structure by flattening the sole with the drum and then use a various rillers and brushing ? I think always using the kuzmin scrapper will wear out the sole quite fast ?


A refresh scrapping will remove 0.01mm of the sole. You can do it many many times. It would even be pretty difficult to wipe a deep linear riller structure from last end of season (old and wet snow) to adapt it to this start season (fresh and cold snow).
So no, I don't constantly scrap. I have two pairs of skis. Also because the stiffness match is much much more important than the structure match.
On my soft pair, on very cold snow I will flatten with the drum and when it becomes warmer I apply manual roller. The stiff pair host a deep linear riller structure. I clean and apply the FP brush.


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