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