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Why does the base angle have so much influence to the grip of the edge?

ScottB

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I have to walk the dog now, but when I get back I will write what I have learned as a ski race coach over the last 5-10 years tuning skis and experimenting with different base and side edge angles. I do agree base angle can make more of a noticeable difference to "grip" than side angle. I have a theory, and there has been some good supporting info posted above by Cantuna and Oldschool. TBD
 

LiquidFeet

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He's talking about how to figure out how far off the snow the edge is when the ski is flat on the snow.

Assuming perfectly flat snow and base, and your edge beveled at 1 degree, and your edge being 1 mm in width from the base, then the height of the sharp edge off the snow would be given by:

1 mm * tan( 1 degree ) = height of sharp edge off snow

I made a rudimentary diagram... "A" is the base bevel, and "H" is what is being calculated. For a 1 mm wide edge (L) and a 1 degree base bevel (A), H is only 0.017 mm which is pretty miniscule.

View attachment 106992

If L is 2 mm, the H is 0.034 mm. If L is 3 mm, then H is 0.051 mm.

@GlacierNovesia is also then talking about the depth of structure, and how that can affect how to treat the side of the base near the edge, because structure depth could affect the height/angle of your edges.

Thank you.
 
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GlacierNovesia

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Sorry for confusion. The question is "why does the base angle has so much influence to the edge grip?"

We have now taken a step back towards the question what we need to apply a small base angle in a technically correct manner.

When we talk about a small base angle you might have this picture in your mind:

BaseNoStructure.png



But that has nothing to do with reality. Because in practice the base always has a structure. Then it will look like this:

BaseWithStructure.png


It doesn't matter if you first apply the structure and then bevel the edge. Or vice versa. A structure has a depth of 20-80 µm. A small base angle has a maximum of 17 µm (H), but only at its outer edge (thanks to @dbostedo for explaining the trigonometric function behind the scene). That is never enough to polish the structure out of the edge. But nobody wants to go skiing with such an roughly edge. Because such an edge has a poor grip and its prone to rust.

So what does a shop normally do? Well, it extends dimension 'L' and it increase the base angle α. Then the edge is already nicely polished. But with the loose of grip. Besides, a service robot doesn't apply an angle. The disc is controlled by a pressure and force curve. And most of the shops (in europe) always use the same setup for every ski. But as long as you always use the same setup regardless of the type of ski and the experience or wishes of the customer, it is more or less a coincidence what comes out in the end.


BaseWithStructurePolished.png


This is the reason why we usually don't have a base angle of 0.5° when you prepare your ski by use of a service robot without any individual machine settings.



But what can we do to have a polished edge and a correct applied base angle of 0.5°? The solution is to apply only a small margin structure between the edges. The structure must stop before the edge. Only if necessary, use a very fine structure near beside the edge. Then you will be able to polish the traces from base preparation (plane grinding) out of the edge:

BaseWithStructureMargin.png


So now the workflow is clear to apply a base angle of 0.5° correctly.

1. check if the ski is plane by use of a true bar, fix holes and scratches
2. flatten the ski as required
3. apply a margin structure
4. bevel side and base edge as required

(only on a top level, not detailled)

Professional world cup machines are able to do it in this way. But professionals frequently use fix file holder to bevel the edges.

Note: a base angle of 0.5° is not a solution for every use case. For GS and off pist you may require a bigger angle and the setup depends also on the ski. A stiff ski is harder to control than a ski with softer flex and torsion. So for GS you may want to have a base angle of 1° or more, but then you don't have to care about polishing the base edge, because 1° or more might be enough to remove the traces of the structure from the edge.

But if you really want to have a base angle of 0.5° or less, there is no other way beside using a margin structure. Except you apply the structure by use of a modern laser, but this will be another story.
 
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Doug Briggs

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I'm late to this discussion and also busy; I haven't read every post. There are a couple of assumptions that I don't agree with although I have no 'proofs'; I'm drawing from my experiences with Wintersteiger products including a Scout and a TrimJet.

First, the structure on the plastic section of the base may or may not be uniformly as deep as that in the edge. Despite the stone being essentially perfectly flat, the surfaces (p-tex and steel) being worked are different and react differently to the stone. The images of universal depth of structure in the p-tex and steel may or may not be what occurs in actual application.

Second, even with a margin structure applied on the stone, structure may be put on the base edges if you have truly blanked your ski. The structure in the 'margins' are very fine, nearly linear structures similar to what you use in blanking. When you blank a ski you are use a uniform, fine linear structure across the entire base of the ski; p-tex and steel edge. This leaves you with a flat base with a very shallow structure. From there you begin to remove material to achieve your desired structure and bevels.

The purpose of blanking skis is to insure that the base edge is prepared in such a fashion that you can actually put the desired bevel on it. This includes removing steel. If the base bevel prior to blanking is higher than the desired bevel, then more steel needs to be removed adjacent to the p-tex than farther from it. If you are a taking base edge to a higher bevel, then you may not have to remove steel at all.

I agree that a wide bevel (bevel the p-tex in addition to the steel) to remove all traces of structure from the edge. It is not a given, however. The greater the desired base edge bevel, the less chance there is of actually structuring the edge. Especially structure that can't easily be remove while setting the base bevel.

I use a process of blanking, 'rough' structure and beveling, then final structure and bevels to reduce the occurrence of structure on skis. Ceramic disks cut steel well but don't cut p-text nearly as well. I do end up scuffing of the p-text next to the edge, but in most cases, brushing will resurrect the structure since the scuffing of p-tex with a ceramic disk doesn't necessarily remove the structure, but flattens it or pushes it over into its grooves. This brushing is akin to brushing your 'helmet hair' and it returning to the desired 'style'.
 

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It doesn't matter if you first apply the structure and then bevel the edge. Or vice versa. A structure has a depth of 20-80 µm. A small base angle has a maximum of 17 µm (H), but only at its outer edge (thanks to @@dbostedo for explaining the trigonometric function behind the scene). That is never enough to polish the structure out of the edge. But nobody wants to go skiing with such an roughly edge. Because such an edge has a poor grip and its prone to rust.

That would be the least of my worries. Structured skis edges are really scary from turn finish, through turn transition and edge engagement at the top of the turn on firm snow. Much worst than hanging burrs.
 

Seldomski

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My guess...

Smaller the base angle, the sooner you begin to dig a trench in the snow with tipping of the ski
Larger "side minus base angle", the deeper the trench that is dug for a certain pressure on the ski

My guess is small base feels more important because you are not skiing on a hard enough surface (ice) or slowly enough for the larger side angle to begin to matter. And if you ski with larger base angle, the small inputs you make (that work with small base angle) will not be enough to get the ski to begin to dig trenches, so the ski feels dull even if the edge is sharp. You end up doing drifted/skidded turns instead.
 

ScottB

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Sorry for confusion. The question is "why does the base angle has so much influence to the edge grip?"

From what I have read on this forum and other web sources: (quoting Oldschool)

Base angle determines, responsiveness to input. How quickly the edge engages. Here the smaller the number, the faster the response Average skier and ski is 1.

Side angle (really net angle = side minus base) controls grip, the bigger the number the more grip.

The side angle typical is a 2 or 3.


I have found the above statements to be true, especially that NET angle (side - base) is a big factor in max grip. So if you lower your base angle from 1.0 to 0.5, you increase your net angle by 0.5 and this will increase your max grip. Most people increase the side angle and leave the base alone, which has the same effect.

Also, keeping the edges sharp (meaning razor like) will make a big difference in grip. Keep in mind all of what I am saying applies ONLY to hard snow or boiler plate. Not necessarily to soft snow.

BASE ANGLE -- I have found base angle to have a big impact on grip, probably equal to side angle. The lower the base angle the greater the net angle, so that just means you have a "sharper or narrower" edge to bite with. That should be self explanatory.

The surprise I found is that with a quicker engaging ski, there is less slip (or no slip) before your edges bite into the snow and this allows for more grip (maybe not more "max" grip, but lets call it more practical grip). My theory is once the ski starts to slide sideways, it is a lot harder to get the edge to bite in. So if it engages quicker, less slide and easier bite. I get a lot more grip at low speeds than high speeds, for a lot of reasons (like lower forces) but I think the main reason is less slide as I start my turn and roll my skis onto their edges. The quicker the edges bite in, the less dynamic sideways force has to be overcome by the edges.

The 3D effects Cantuna posted about are in play here as well. When you first roll the ski on edge, it is starting to flex and the entire edge is not in contact with the surface. I don't claim to understand all the physics involved with flex and edge grip of a ski, but experience has proven to me the base bevel is a big factor in grip, because it allows the edge to engage quicker (with less ankle roll).

I have skied on a lot of skis with base bevels as low as 0.25 (which I really liked) and as high as 4.0 degrees (which I hated). Anything above 1.5 to 2.0 range causes grip issues on boiler plate for me. Side angles I have skied varied from 1 to 7 degrees. I personally like all my skis at 0.5 base and 3.0 side. That is where my powder ski is set at. It allows for some grip on ice, and doesn't matter in the powder.

In New England, there is always some ice, so I want my skis to handle it when I encounter it. My rockered skis feel different with that tune than my race skis, because of the ski construction, and I don't mind the way my rockered skis feel with that tune. They would be easier to ski with a 1.0 / 2.0 tune, but I like the precision. This is a personal preference. The sharpness is very personal as well, and any new ski I get has to be dialed in for sharpness, angles, sharp tip to tail or not, ect.... Once I ski it, I tend to know what to adjust, and then I just keep the same and resharpen the side edge every few times I use a ski. I almost never touch the base bevel, except for deburring. Pretty standard stuff, since I spend a lot of time on "ice" and weigh around 240 lbs, grip is very important to keeping me on my feet and in control. The less you weigh and the slower you ski, I think you will not need as much side angle and may appreciate a 1.0 base which allows more "slarve" in your turns.
 

ScottB

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My guess...
And if you ski with larger base angle, the small inputs you make (that work with small base angle) will not be enough to get the ski to begin to dig trenches, so the ski feels dull even if the edge is sharp.

I demo'd a ski with really sharp feeling edges and had the exact experience you described. I took it back to the shop and had them measure the base angle, it was 2.0 degrees. I had the ski tip slide sideways off the top of a mogul just as I was about to a make turn. Almost pulled my groin. I am used to skiing small base bevels. When I really cranked the ski over, I would get grip, but it felt very strange just as you describe.
 

Dave Marshak

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I agree that a wide bevel (bevel the p-tex in addition to the steel) to remove all traces of structure from the edge. It is not a given, however. The greater the desired base edge bevel, the less chance there is of actually structuring the edge.
I'm mostly agnostic about this subject because I have no way of measuring the base angle so I never know what I'm actually skiing. I'm skeptical that I could notice the difference between 0.5 and 1 degree because the difference in edge height above the base is only about 0.02 mm. That's less than the diameter of the snow particles you're skiing on.
OTOH what is the true variable? Does a ski with a wide 0.5 bevel ski the same as one with an edge-only bevel? or more like a ski with an edge-only 1 degree bevel? I'm guessing a wider bevel would have a similar effect as more angle, but I have nothing to back that up.

dm
 
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GlacierNovesia

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I'm mostly agnostic about this subject because I have no way of measuring the base angle so I never know what I'm actually skiing.
This is simple. Either you use a set of fix file holder, e.g. in steps of 0.5°, .075° and 1° and an edding. Then you can test the angle as demonstrated here in this video. Or you use a true bar and a high precision feeler gauge with 10 µm steps to check the distance between edge and true bar.

You can use this table to get the base angle equivalent in dependence of the distance:

distancebase angle (equivalent)
10µ0.3°
20µ0.6°
30µ0.9°
40µ1.1°
50µ1.4°
60µ1.7°
70µ2.0°
This table tells not the truth. Only in the case that the base is 100% flat and the base angle starts exactly 2 mm far from the tip of the edge. For other situations you have to use a pocket calculator and the trigonometric tan-function. Or you may use a side and base angle gauge for ski. Or the high sophistic alternative with digital display. Now you have no excuse any more. ;)


Most of the guys that I know who tune their skis themselfes or know a shop with a race service or a world cup tuning machine say, that the base angle rulez. Of course, the net effective edge angle has also high impact to the edge grip. But at least if the base angle becomes too big you will almost have no grip on ice and hard snow.
 
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ScottB

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A point that has not been made yet is how far do you have to roll the ski over till the edge bites in. I used to think it was just you roll it to the base bevel angle and then it starts to bite, but I don't think that's right at all. I think you have to probably roll it another 10 degrees to get it to bite in. If you think about it, you are not pushing your sharp inside edge into the snow, you are dragging the edge in the opposite direction until it is at a large enough angle to bite in and stop any side slipping. Think about using a snow shovel. You are pushing the edge of the shovel into the snow. Turning a ski is the equivalent of pulling the shovel backwards and making it bite in by pushing down on it. Think about the angle and force needed to prevent the shovel from sliding backwards.

I would also like to point out that a side edge angle of 5 degree is extreme, so if you go from a 1.3 base angle to a .5 base angle, the change in NET angle is a lot considering the typical range.
 

cantunamunch

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I think nobody has made a point like that because we don't have strict definitions of where the fulcrum/pivot is at any give phase of edging. It cannot be at the sharp edge when the ski is flat. Is it at the midline of the ski? Is it at the edge/base interface, where the bevel starts?

I have no problem with asserting that we tip a ski 10 or more degrees past edge contact, but after the edge contact occurs, the fulcrum is completely defined to be at the sharp edge. Just that observation is enough to explain the dependence of ski feel on base bevel angle.
 
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GlacierNovesia

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Well, I still have another theory. If you want to cut a nice piece of steak with a sharp Japanese knife, it won't work if you take the wrong side. The cutting edge cut the steak .

For the ski to cut the snow, the edge must have contact with the snow. Sounds simple, or not?

If we assume that our edge is a Japanese knife, the cutting edge is always in contact with the snow. Within a normal range of movement, the edge will cut the snow with a probability of 1 or 100%.

Knife.png

Fig. a, Japanese knife

Who has ever used a ski with a concave base? Such a ski cuts well, but you can hardly slip. The reason here is that the edge almost always has contact with the snow. By the way, the same effect occurs if the edge has a burr. Again, within a normal range of movement, the edge will cut the snow with a probability of 1 or 100%.

Konkav.png

Fig. b, concave base

Now let's look at a real ski.

SkiEdge.png

Fig. c, real ski

As we can see, we now have two contact points to the snow. The very blunt edge at the transition from base to edge and the edge itself. But the probability that the edge is in contact with the snow is significantly lower than in the previous pictures. Within a normal range of movement, the edge will cut the snow with a probability less than 1. Something in between a range of 0 and 1.

So here we have a relationship between the base angle and the probability with which the edge cuts the snow. And apparently this gets smaller quickly with a larger base angle.

Maybe we need a mixture of all theories to explain the influence of the base angle.

What do you think about this?
 
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ScottB

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Sorry for confusion. The question is "why does the base angle has so much influence to the edge grip?"

Here is a diagram to explain what I mean about how an edge bites into the snow. When you are turning a ski, the turn force (or centripital force) is trying to make the edge back out of biting into the ice. The skiers weight and the tip angle is driving it into the snow. The first diagram is the ski flat on a flat ice surface. The next is tipped at the base bevel angle, 0.5 degrees and the edges are just touching the ice but not biting into it, and the last is the ski tipped at 15 deg angle and the edge biting into the ice. I don't know how much angle it takes to get the "bite".(greater than 0.5 deg and I would guess less than 15 deg) But NET ANGLE is a major factor, along with a whole lot of other factors I believe.



1596057814816.png
 

Seldomski

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Back to the point about responsiveness -- and more trig!

How much knee movement does it take to rotate the ski very small angles- say to get the ski from base, through the bevel, and to touch the edge? This will depend on your shin length. Let's pretend your knee is 0.55m from the snow surface (50 percentile male).

My favorite MIL standard.

Knee height x sin(base angle) ~ knee lateral motion to rotate ski base.

.5 deg base -> 4.8mm (3/16"). There is a deadband of 9.6 mm (3/8") of knee movement where the ski edge doesn't do much.
1 deg base -> 9.6mm (3/8"). There is a deadband of 19.2 mm (3/4") of knee movement where the ski edge doesn't do much.

Get a ruler and mark a dot on your knee. Sit in a chair with your feet flat and move your knee so the dot travels laterally along the ruler and see how much more precise the 0.5 deg base is vs 1 deg.
 
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dbostedo

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From your reference:
I've been seeing pages like this for over 30 years now, and I still laugh.
"Fail! It's not blank!"
View attachment 107086
I always think they should have a page just before that that reads "Next Page Intentionally Left Blank", and then have a truly blank page after it.
 

James

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I always think they should have a page just before that that reads "Next Page Intentionally Left Blank", and then have a truly blank page after it.

It all depends on how you define blank. Technically, just a page number means it’s not blank.
Just like defining “full”.
3F6561A1-05F3-43A0-883F-24615D264CC0.jpeg
 

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