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

[GlacierNovesia]

A couple of years ago I have started to prepare my skis by myself beause I was not very happy with the results of normal consumer full automated service (in Europe, mostly Germany, Austria and Switzerland). They never apply a base angle of 0.5° even if they tell you to do so and most of the machines grind to much into the base instead of stopping before. And I figured out that only professional tuning machines are able to apply the base angle correctly but they are very rare. You will find such machines at such locations where professionals do their training.

At least I found out that a base angle between 0 and 0.75° has more impact on the grip of the edge than a effective angle of 89° or 85°. But why?

Does anyonoe have an explanation why the base angle is so much more important than the side angle?

Peter

 

[James]

Well a 5 degree side edge will have quite an effect- once you get it to bite. The base edge influences when/how quickly the edge bites. So that’s pretty much why it has so much effect. It’s pretty much the response of the ski.

I believe @ScottB got a pair of race or carving skis last season that had like a 2 deg base and a 7 deg side edge. Once engaged, it was extremely difficult to disengage.

 

[NZRob]

Interested in the response too....like you @GlacierNovesia I started doing my own tuning in earnest a few years ago after one too many sh*t tunes from a shop.

 

[oldschoolskier]

Net angle controls grip (side minus base), the bigger the number the more grip.

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

The side works based on this, here the typical is a 2 or 3.

Net angle is a 1 or 2 (89 or 88). Factors that influence this are ski construction, intended use, ability, conditions and preference.

Finally, there are hidden factors that can greatly influence appearance of tune and that is burrs, intentional (high end race specialty tunes, insane grip) or unintentional (poor tunes.

I like a 0.5/4 across all my skis (no burrs), extremely fast engagement with great grip (too fast and grippy for most), I tune my family (and few friends) with a 1/3 (no burrs), grip with a touch of forgiveness.

Sequence of tune, set base first and touching up on subsequent tuned (and leave alone, very little is required here other than to ensure no burrs). Side after base , set angle and maintain to hold grip (most work and upkeep is done here). Care must be taken or unintentional hanging burrs occur, this is bad.

 

[GlacierNovesia]

Interested in the response too....like you @GlacierNovesia I started doing my own tuning in earnest a few years ago after one too many sh*t tunes from a shop.

Well, I don't know the situation in north america. But in europe most of the shops prepare all the ski with the same setup. But when you want to apply a base angle of 0.5°, the outer edge is 17 µm behind the base (tan(0.5°) * 2 mm, the usual thickness of a consumer ski edge). But most of the shops apply the structure over the whole base of the ski and this is wrong. Because for alpine skiing a structure has a depth between 20 µm and 80 µm. So the only way to polish the structure out of the base edge is to apply an angle much more than 0.5° or grind wide into the base. Thats the reason why experts apply the structure only in a small stripe that is smaller than the distance between the edges at their smallest location under the binding, as you can see in this video: Toko tuning video

So it it impossible to have the structure over all the whole width of the base from tip to end, a well polished base edge and a base angle of 0.5°. But for the shops its much more simplier to service all skis with the same setup instead of modifiing the setup for every pair of skis. Even if is this a question of seconds with a modern service robot.

Well a 5 degree side edge will have quite an effect- once you get it to bite. The base edge influences when/how quickly the edge bites. So that’s pretty much why it has so much effect. It’s pretty much the response of the ski.

Well, of course, the side edge angle makes the ski more aggressive too. But when you apply a base edge of 2° or more, you will have almost no grip on ice or compressed machine snown. Regardless of the side angle. Even experts are not able to feel the difference between a 88° or 87° setup. But the difference between 0.5° and 1° at the base is tremendous. Not to mention the difference between 0° and 0.5° (0° impossible for me to ski)

 

[graham418]

I am always amazed how much difference .5 of a degree makes in the feel of the ski, considering that in absolute measurements the difference across a 3mm edge is about .025 mm

 

[GlacierNovesia]

^^
The most plausible explanation so far that occurs to me is that a wider base angle or a very poorly executed service lever the edge out of the snow and therefore the ski
loses grip. But that's just a theory, I still hope that someone has a physical explanation for it.

 

[James]

Thats the reason why experts apply the structure only in a small stripe that is smaller than the distance between the edges at their smallest location under the binding, as you can see in this video: Toko tuning video

Blanking of the structure near the edges has nothing to do with what you’re talking about. It’s a relatively new development too. Maybe 5 yrs? Without computer controlled stone dressing, it would be very difficult.

But when you apply a base edge of 2° or more, you will have almost no grip on ice or compressed machine snown. Regardless of the side angle.

You just need to throw on more platform angle right away. It’ll grip, but it may be too late in the sequence of the turn especially if you don’t give it what amounts to violent application of edge angle relative to normal. On the other hand, if you’re skiing in trees with firm snow present, it might be beneficial. Having a 0.5 base hook up because of an undulating chaotic surface isn’t fun with trees present.

Even experts are not able to feel the difference between a 88° or 87° setup

Not true either. Where are you getting this? Even in some types of soft snow, like wet dense, you can tell a sharp edge.

 

[cantunamunch]

^^
The most plausible explanation so far that occurs to me is that a wider base angle or a very poorly executed service lever the edge out of the snow and therefore the ski
loses grip. But that's just a theory, I still hope that someone has a physical explanation for it.

You're still thinking in two dimensions only, and I think that's a mistake.

Base edge is one of the parameters that influence our perception of ski flex, both torsionally and longitudinally. But let's ignore torsional flex for a moment -set it to an ideal zero - and consider longitudinal only.

Start thinking about very early onset of edging input - before the ski is flexed into its full on carving shape. Let's leave fully rigid ice skates and super-stiff rockered skis aside for the purposes of discussion. Every other ski out there takes up both time and, therefore, space, to achieve a carving configuration.

On a conventionally flexed, conventionally cambered ski, longitudinal flex of the ski *starts* when the forward contact point engages to hold the surface, and progresses towards the center of the ski as the edge corresponding to that section of ski engages the snow.

Now picture two hypothetical skis - one with a consistent 0.5 degree base angle and one with 0.5 alternating with 3 degrees in 5cm segments. Same skier, same slope, same quickness of edging inputs.

How will the two skis act differently to load the longitudinal flex of the ski?

(BTW if this thought experiment makes you think that sidecut shape will play a role - yes. Two dimensional, steady state coronal plane analysis doesn't even begin to explain modern skis)

 

[GlacierNovesia]

Blanking of the structure near the edges has nothing to do with what you’re talking about. It’s a relatively new development too. Maybe 5 yrs? Without computer controlled stone dressing, it would be very difficult.

Well, the video has been published in 2013. But its definetly no rocket science. After plane grinding the ski you just have to limit the width of the structure to the minimum base width of the ski, thats it. And with a structure riller it is very easy. I assume that the service men in the world cup have always prepared the ski in this way. Because otherwise they were not been able to to bevel the base angle with 0.5° or less correctly.

Not true either. Where are you getting this? Even in some types of soft snow, like wet dense, you can tell a sharp edge.

From a site unfortunately only available in german: Perfect Skiservice In 6 Steps

Step 5: edge tuning

[.....] Anyone who speaks to World Cup service people knows, however, that even World Cup professionals are often unable to distinguish between an edge angle of 86 ° and 87 ° in the blind test.
[.....] In contrast to the side covering angle, the layman will also be able to distinguish between nuances in the quarter-degree range [regarding the base angle]

Having a 0.5 base hook up because of an undulating chaotic surface isn’t fun with trees present.

Your are absolutely right. Even under very good conditions it is not fun to ski with a slalom carver with a base angle of 0.5°. Thats the reason why I use 0.75° for the first 10 inch from tip and tail.

 

[GlacierNovesia]

@cantunamunch

That's a good point

 

[SpikeDog]

Congratulations on taking tuning into your own hands, Glacier. Typically it's a really bad shop tune that pushes you into it, but you'll quickly learn that it's a very important step in becoming a better skier.

 

[James]

I assume that the service men in the world cup have always prepared the ski in this way. Because otherwise they were not been able to to bevel the base angle with 0.5° or less correctly.

Yeah, that assumption is wrong. They have not always blanked the sides, and they don’t always do it. It’s called a margin.

Make it ten years, it’s pretty new and places still don’t routinely do it. Again, despite what you think, edge to edge structure was around and standard long before margin structures existed.
It’s my understanding that say 15-20 (or more) years ago, flattening of skis in shops was routinely done on belt machines with automaic feed and bridges for the binding. (Not talking hand held ski with Grindrite machines.) Then it would be stoneground. Because of the flex in the rubber roller supporting the belt, the ski would end up with at least a 0.5 bevel, so with that setup it wasn’t possible to have less than a 0.5 base bevel.

I believe skis that come in with questionable bases are still done this way. Good chance it’s even hand held.
See this thread-

can put a structure in a ski from edge to edge then apply the base bevel, resulting in no structure in the edge and an edge to edge structure. Most speed skis have edge to edge structure and I'd wager a beer that not one of those edges (on the WC at least) has structure in them.

It can be desirable to have structure from edge to edge. The key is to bevel the base edge after the structure is ground into the ski. It is possible to run a structure pass over a ski, achieve edge to edge structure and not structure the base edge. It depends on the pressure of the stone and the bevel of the base. There is no right or wrong process, just good and bad results.

Travis Ganong Wcup ski.

 

[Wilhelmson]

A couple of years ago I have started to prepare my skis by myself beause I was not very happy with the results of normal consumer full automated service (in Europe, mostly Germany, Austria and Switzerland). They never apply a base angle of 0.5° even if they tell you to do so and most of the machines grind to much into the base instead of stopping before. And I figured out that only professional tuning machines are able to apply the base angle correctly but they are very rare. You will find such machines at such locations where professionals do their training.

At least I found out that a base angle between 0 and 0.75° has more impact on the grip of the edge than a effective angle of 89° or 85°. But why?

Does anyonoe have an explanation why the base angle is so much more important than the side angle?

Peter

The ski base is flat so it needs only a small angle to temper the response of the ski when tipped. If you had a large base angle your feet/ankles would be tipped at max before engaging the edge.

 

[GlacierNovesia]

can put a structure in a ski from edge to edge then apply the base bevel, resulting in no structure in the edge and an edge to edge structure. Most speed skis have edge to edge structure and I'd wager a beer that not one of those edges (on the WC at least) has structure in them.

It can be desirable to have structure from edge to edge. The key is to bevel the base edge after the structure is ground into the ski. It is possible to run a structure pass over a ski, achieve edge to edge structure and not structure the base edge. It depends on the pressure of the stone and the bevel of the base. There is no right or wrong process, just good and bad results.

OK, you are right. In speed disciplines gliding is much more important than edge grip. For that they file the edge down to one millimeter (because the base glides better than the metal edge) and of course they need a structure from edge to egde. But, in this case they will have no base angle 0.5°. Because such a small angle would be too dangerous. As far a I remember they use base angles of ~ 1° or more in speed disciplines.

The thread that you linked looks very interesting. I will have a look later.

can put a structure in a ski from edge to edge then apply the base bevel, resulting in no structure in the edge and an edge to edge structure

That depends on the depth of the structure and the base angle. If you have a middle structure of 50 μm it is impossible to apply a base bevel of only 0.5°. If you don't accept structure in the edge of your ski. You have to choose an angle of ~ 1° (tan( 1°) * 1 mm = 17 μm and you have to grind into the base. You can see this in the picture that you have posted. The structure does not stop right at the edge, it ends ~ 1 millimeter before.

 

[NZRob]

Well that all went over my head very quickly

 

[LiquidFeet]

@GlacierNovesia, when you post and talk about ski tuning in other locations, do you find skiers there who also use mathematical terms such as ~ 1° (tan( 1°) * 1 mm = 17 μm?

I don't know what this mathematical phrase adds to this discussion about edges that can't be explained by talking about degrees. Can you explain what it adds to someone (me) who doesn't use such concepts?

 

[ScottB]

I think GlacierN is mixing some things up, but his trig is OK. He is writing arc tangent equations, which is probably still greek to most people. What he is saying is the amount of material you remove from an edge to get a 1 degree base bevel is very small, .017mm I believe. I think that is a little low, the trig is dependent on how wide you assume your edges are (I think they are 1.5-2 mm), he assumed 1 mm wide. Am I correct Glacier?? A diagram would help.

What I think is misunderstood, is you grind a base flat, edge to edge across the Ptex. then you apply the structure, which creates creates some recesses, but does not lower the entire base and make your edges high. The ski is still flat across the width. Then you come in with a stone that only touches the edges and put the 0.5 deg. base bevel on, only to the edge and not the structure.

Someone who actually operates a machine would know the process better than me, but after talking to SKIMD a lot, that is my understanding. He has put a 0.25 base bevel, 4 deg side edge, and his WC structure on my skis and they are as flat as can be and the base bevel is perfect tip to tail. He is very, very good and does all my skis to whatever I request him to do.

 

[dbostedo]

Can you explain what it adds to someone (me) who doesn't use such concepts?

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.

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.

 

[ScottB]