Actually I did everything in less than 30 minutes. SEM is quite easy to use, almost as easy as an optical microscope. It is not the best instrument for surface analysis: the AFM (Atomic force Microscope) is the best to make surface topography; it is smaller and as easy to use as the SEM. We have one in the lab, and it is seldom used, but I never worked with it...
I was thinking that the scraper will make the surface smoother, so it will look closer to the waxed surface. I wonder if it worth to try with a scraping plane:
A grooved blade is also available, to make some strustrure on the base:
These tools are used to smooth the surface of hard wood and veneers.
Superb pictures!
Gives a good vision of what happens after waxing.
I was also thinking that using this kind of microscopic pictures we could maybe find out what is the best way of surface and flame treatment for UHMWPE sidewalls.
Really great stuff there Davide. I doubt that many of the big ski manufacturers have access to this kind of technology. They'll need to visit skibuilders.com to get the latest research. Obviously, most of us garage craftspeople are not experienced in interpreting this sort of data, but, to my untrained eye, it looks like the hand-scraped UHMW base is the smoothest of the examples that you have examined so far. What is your opinion? And, is it okay to suppose that a base that is the most smooth at 500X magnification in the lab will also run the most smooth when placed on the snow? Thoughts anyone. Thanks again, Davide, for the great work.
This is the scraped base, with inclined sample holder.
Down here is the way I explain the whole thing, based on what I have understood.
The base should not be too smooth, otherwise the water layer will extend through the whole ski and the friction will increase. If the base surface is too coarse, the water layer almost disappear, and the friction increase (no more water to lubricate the surfaces).
The best is an intermediate situation. I think that scraping in the right way, it would be possible to achive the same degree of smoothness that using stone griding and waxing. The polythilene is already water repellent, so the wax will not improve the idrophobicity.
I think that the next step, is to prepare a pair of skis only with the scraper (no wax) and see how they glide...
That is what I will do on the next pair I will build.
I have been a professional ski technician for 8 years now, and I would like to share my knowledge/opinions on these subjects.
Different structures in the base material can be achieved using stone grinding, depending on how the stone has been dressed (cut with a diamond). The structure is there to channel moisture. In warm, spring snow, there is far more moisture, so you need a deeper structure to channel that much moisture. Alternately, in cold, fine snow, a deep structure would act like a bunch of tiny suction cups, so a shallower, finer structure is used for these conditions.
Many of the ideas behind waxing are largely misunderstood. Most people think of the wax as a lube, to make you go faster, but this is not the case. What wax actually does is creates friction, to create the micro layer of water that you ski on. Different temperature waxes are different hardnesses, to try and match the snow. Also, many people think the wax is there to protect the base. This is partially true. On a properly tuned ski, 95% of the wax is scraped off, so you're not actually skiing on the wax, you are skiing on the base. So, the wax isn't there for added abrasion resistance, but is does soak in, because the base is porous (unless it is extruded, in which case, waxing is almost fully fruitless). The wax soaking in helps prevent oxidation.
This oxidation can be scraped off with a metal scraper, but by doing that, you minuteley change the geometry of the bottom of the ski. If you just scraped an alpine ski with a metal scraper, and never had it ground, it would become concave. In my experience, the geometry of the bottom of the ski is just as important as the other design factors of the ski, if not more important, because it's the part of the ski that actually interacts with the snow. For example, I tried a pair of brand new skis off the rack, and didn't like them. After I tuned them up with different bevels, and took them back out, they were completely different.
The geometry of a ski in regards to tuning involves three factors, the base, the base edge bevel and the side edge bevel. A ski should be flat across the width of it's base, for best predictability. The base bevel is usually between 0 and 1 degrees, while the side edge is usually between 0 and 3 degrees.
Pores appear to be a key issue here and Kuzmin argues that the base material is free of pores. Would it be possible for you to look at the surface at higher magnification (5000x maybe?), to see if you can find any?
Sintered UHMWPE has lots of pores, extruded may have some, but a lot less. The pores act as storage for the wax, given that the base has been waxed properly. Test have been performed showing wax layer on the surface of skis intact after 30km (cross country).
Kuzmins article was widely discussed on release, but no response has been given to cricism from other reseachers. The paper has been refuted by numerous people.
Svimen wrote:Sintered UHMWPE has lots of pores, extruded may have some, but a lot less. The pores act as storage for the wax, given that the base has been waxed properly.
It would be nice if one day somebody will post some pictures of UHMWPE pores... Haven't yet seen them.
Here http://skinnyski.com/gear/display.asp?Id=4430 they said: "We can wax a base and then measure exactly how much wax is in the base. We can even see how deep the wax has penetrated by slicing off 1/1000m pieces off and analyzing it"
So why do not they publish this numbers?
The amount of wax in the base is ridicolous small, and the penetration depth is in the micron range.
I just repeat that a friend of mine got a pair of secondhand Pocket Rocket 3 years ago. He uses them around 100 days per season, and he never waxed the skis in 3 years: the base is so dry it is almost white. They are faster than brand new skis. I have seen it.
I would believe that wax is a key factor in world cup races, but for everyday use its importance is overestimated by far.
I find it hard to believe that a properly waxed ski is slower than an unwaxed ski. Im sure most major ski manufacturers that supply skis to world cup racers have explored this area and if they thought a racer could go faster and win on their skis by not waxing them, then racers would not wax their skis.
I think there are at least two significant factors when people find an unwaxed ski to be faster than a waxed ski...
1. The waxed ski has to have a wax appropriate to the snow temp. If you try and use a warm temp wax on really cold snow you might start to think you used glue instead of wax. In which case just about anything will seem faster.
2. Bases do tend to get faster with age after a stone grind. When the bases is belt sanded/stone ground, it creates lots of little ptex hairs. These hairs can mostly be removed through a series of waxings or with base shavers or scotchbrite pads, etc. Despite best efforts you will probably not get every little microscopic hair off. Through use the amount and size of hairs left will be reduced and produce a faster ski.
The above are strictly opinions based on my experiences, readings, and thoughts. But short of actual tests of various base preparations compared under controlled conditions I will continue to use wax.
Rich C wrote:
1. The waxed ski has to have a wax appropriate to the snow temp. If you try and use a warm temp wax on really cold snow you might start to think you used glue instead of wax. In which case just about anything will seem faster.
Well, people usually wax the skis at the beginning of the season, and then they use them till spring without re-waxing them. I never met somebody who wax his skis each time going skiing according to the snow he will find.
By the way, the companies sell universal wax, that meens that the appropriate wax (red, yellow, blue) is not that important in everyday skiing.
Rich C wrote:
The above are strictly opinions based on my experiences, readings, and thoughts. But short of actual tests of various base preparations compared under controlled conditions I will continue to use wax.
Well, you should just try once scraping the base, and if it does not work, then you can still wax it. I will do that on the neew pair I'm building.
World cup is a different thing. If a base preparation allows to go 1% faster, then they will do it (1% over 80 seconds is longer than one second), but for everyday skiing, 1% is just nothing: you notice that only with a cronometer.
The sintering process in itself is what creates pores in the base material.
Powdered uhmwpe is put in a form similar to that of a cheese (not wedge, but whole cheese), the entire thing is then heated to a point below the melting point of the material but still hot enough to make the individual particles of powder adhere to each other. The powder is not melted, thus the air between the particles is retained in the final product as gaps between particles of uhmwpe.
Base material is then "shaved" off the "cheese" to make base materials. The material in the "cheese" is not uniformly melted, so that variations ocur in the material. The "best" material is kept by the ski manufacturer and used only in the skis for their top athletes.
Sintered uhmwpe thus has different qualities, and it is quite possible that the stuff we can get our hands on is not very high quality, and also that it therefore contains less pores.
My point earlier has not been thet waxing is super important, but i think it is important that the problems in Kuzmins paper are exposed. He might still be right about some things, indeed it may be that for recreational skiing it does not matter wether you wax or not, as the wax has to be finetuned to the conditions of any given day to be optimally beneficial.
Stark claims such as Kuzmins are often discredited on general principle by scientists, and it is always important to be open to new theories in science, however such claims are more often than not proven to be erroneous. Science is most often small incremental steps, not great leaps forward.
While I can't comment on any scienific data, I can speak from 17 years of working and riding on snow. Trust me racing or recreation, a proper wax job and structure make a huge diffrence. the idea that a dry base would have a positive effect on downhill ski/boarding just doesn't work. If it did we would have stopped waxing our rental ski/boards years ago. As it is we get enough complaints from returning customers about the lack of glide in unserviced rentals(happens during peak holidays)
