Edge Bevels redux: 1 and 2 vs 1 and 3?

[François Pugh]

It's how far you have to turn your steering wheel before your car notices that you don't want to continue going straight, not how quick the steering ratio is (or how many turns lock to lock).

 

[Tom351]

It's how far you have to turn your steering wheel before your car notices that you don't want to continue going straight, not how quick the steering ratio is (or how many turns lock to lock).

Agreed- excessive bevel would be similar to a worn out car with a bunch of "slop" across center in the steering.

 

[cantunamunch]

So - I take it none of you have a pair of 2-3 degree base bevel skis for steep spring slop?

 

[Juha]

Hello,
If you see my picture above it tries to describe a sidecut of a ski - edge is on the left side. All the tuning tradition says one should file the base bevel to the whole width of the base edge. Meaning line B in the picture above. All the tradition says is one should mark the base egde with a marker pen to see when the whole edge is filed.
The reasoning why one should file the width of the whole base edge has not been that often explained, which has been bothering me a bit.
Just to reason it for myself I took a few minutes to calculate is it about the angle needed to engage the edge..
OK, let's assume that instead of filing the whole width of a base edge, say 2 mm, we just would file 1/3 of the width, that means 0.66 mm. Let the line A in my picture be this base bevel. Let's also assume both base edges are at 0.5 degree angle.
In trigonometry tan alpha = length of opposite/adjacent.
If we cut according to line B, the height of the cut is 0.0175 mm. If we cut along line A, the height of the cut is 0.0058 mm.
OK, all fine.. What does this mean to difference in angle to engage the edge. Let's assume we have a narrow SL ski that is approx 64 mm wide in the middle. Being flat on the ski, the center of mass should go via the middle of the ski, ke. The distance from the edge is 32mm. So how much angle do we need to engage edge that is cut along line B? Again let's use the same formula and solve tan alpha = (0.0157/32). The angle is 0.031 degrees.
In the case of line A then tan alpha = (0.0058/32). The angle is 0.010 degrees. Just a difference of mere 0.02 degrees.
Can anyone really feel that difference when initiating the turn? This cannot be the reason for filing the whole base edge width, can it?
Second thought that came to my mind when looking at the picture is that when you cut the base edge along line B, the height of the cut gets smaller when you go on and make edged thinner by sharpening the side edge, so eventually when side edge is almost worn out, you end up in similar 'clearance' as with if starting with line A.

Please let me know if I made a mistake in my calculation above or what is the reason for the traditional wisdom of filing the whole width of the base edge at once?

 

[ScottB]

I would say you rotate the same angle for both lines A and B. Edges only work on hard snow. Assume ski stays on top of the "ice". Ski rotates about intersection of line A or B with base line. Both lines have the same angle, so same rotation. You probably need to rotate past the point where the sharp edge just touches the ice, how much I don't know, but a few more degrees I would think. The other effect that happens is the included angle of the side wall and the beveled bottom edge changes when you change your base bevel. This is not your case here, but is significant to how quickly and forcefully the edges bite into the snow.

I would guess the real world reason (not trig theory) to bevel the entire width of the base edge is to get it a little bit off the snow. Snow, ice, skiing surfaces are not perfectly flat, so the gap between edge and snow needs to be above some minimum to go along with the base bevel angle. This is my guess, others may have a better understanding than me??

 

[Atomicman]

In reality it is more likely you will end up beveling the entire width of the edge and some base.......long bevel, not just a portion of the edge. How would you even only bevel part of the base edge with a proper file and guide?

 

[Atomicman]

So - I take it none of you have a pair of 2-3 degree base bevel skis for steep spring slop?

C.mon CTM, You know better....since the surface is so soft and "movable" no need for a bunch of base bevel!

 

[Juha]

I would guess the real world reason (not trig theory) to bevel the entire width of the base edge is to get it a little bit off the snow. Snow, ice, skiing surfaces are not perfectly flat, so the gap between edge and snow needs to be above some minimum to go along with the base bevel angle. This is my guess, others may have a better understanding than me??

Thanks,
As my calculation shows we are talking about hundreds of a millimeters, so it is very small clearance when running on a perfectly flat ski and the snow is not that even either. Besides, who skis on a flat ski in SL or GS? Sometimes in DH this is possible and in recreational skiing more often.

Any other good ideas and input anyone?

 

[James]

It’s unlikely you’ll get a truly flat ski from a grinder. Most will have a small amount of bevel. I suppose it’s possible.
Don’t see how you could make just part of the edge beveled, esp by hand. Everything is fighting against such precision.

 

[Jacques]

View attachment 98351
Hello,
If you see my picture above it tries to describe a sidecut of a ski - edge is on the left side. All the tuning tradition says one should file the base bevel to the whole width of the base edge. Meaning line B in the picture above. All the tradition says is one should mark the base egde with a marker pen to see when the whole edge is filed.
The reasoning why one should file the width of the whole base edge has not been that often explained, which has been bothering me a bit.
Just to reason it for myself I took a few minutes to calculate is it about the angle needed to engage the edge..
OK, let's assume that instead of filing the whole width of a base edge, say 2 mm, we just would file 1/3 of the width, that means 0.66 mm. Let the line A in my picture be this base bevel. Let's also assume both base edges are at 0.5 degree angle.
In trigonometry tan alpha = length of opposite/adjacent.
If we cut according to line B, the height of the cut is 0.0175 mm. If we cut along line A, the height of the cut is 0.0058 mm.
OK, all fine.. What does this mean to difference in angle to engage the edge. Let's assume we have a narrow SL ski that is approx 64 mm wide in the middle. Being flat on the ski, the center of mass should go via the middle of the ski, ke. The distance from the edge is 32mm. So how much angle do we need to engage edge that is cut along line B? Again let's use the same formula and solve tan alpha = (0.0157/32). The angle is 0.031 degrees.
In the case of line A then tan alpha = (0.0058/32). The angle is 0.010 degrees. Just a difference of mere 0.02 degrees.
Can anyone really feel that difference when initiating the turn? This cannot be the reason for filing the whole base edge width, can it?
Second thought that came to my mind when looking at the picture is that when you cut the base edge along line B, the height of the cut gets smaller when you go on and make edged thinner by sharpening the side edge, so eventually when side edge is almost worn out, you end up in similar 'clearance' as with if starting with line A.

Please let me know if I made a mistake in my calculation above or what is the reason for the traditional wisdom of filing the whole width of the base edge at once?

Is this a "pipe dream"?

 

[Dave Marshak]

I'm sure base angles make a difference, I just don't know anyone who ever did a controlled experiment to determine what those differences are. I also think there's a lot of confirmation bias going on, even among serious racers.

For one thing, you're talking about differences of thousandths of an inch on an edge that runs over a surface that varies far more than that. For another, I can't accurately measure what my actual edge angles are, even if I do them myself, and I'm pretty sure I get the same angles from the shop as everybody else, no matter what I tell them. I'm not even sure we are discussing the right variables. If I have a 1 degree bevel that's only half the width of the edge, does that ski like 1 degree or more like 0.5? Getting the width of the base bevel perfect seems like something pretty difficult to control for, on a shop machine or with hand tools. Your tuning skills may be better than mine.

Finally, side bevel doesn't matter much at all until the snow is hard enough that setting the edge becomes difficult. Even then, a sharp 2 degrees is way better than a dull 4.

dm

 

[TheArchitect]

I switched to a .5/3 for all but my powder skis. I couldn't tell you whether it was side or base or both bevels that made the difference but I do know that I'd never go back. Whenever I buy skis I bring them to SkiMD and have Mike do a "Factory Fresh" tune and then I take it from there for regular waxing and edge touch-up.

 

[Atomicman]

I'm sure base angles make a difference, I just don't know anyone who ever did a controlled experiment to determine what those differences are. I also think there's a lot of confirmation bias going on, even among serious racers.

For one thing, you're talking about differences of thousandths of an inch on an edge that runs over a surface that varies far more than that. For another, I can't accurately measure what my actual edge angles are, even if I do them myself, and I'm pretty sure I get the same angles from the shop as everybody else, no matter what I tell them. I'm not even sure we are discussing the right variables. If I have a 1 degree bevel that's only half the width of the edge, does that ski like 1 degree or more like 0.5? Getting the width of the base bevel perfect seems like something pretty difficult to control for, on a shop machine or with hand tools. Your tuning skills may be better than mine.

Finally, side bevel doesn't matter much at all until the snow is hard enough that setting the edge becomes difficult. Even then, a sharp 2 degrees is way better than a dull 4.

dm

You don't need to do a controlled experiment to know what the differences in base bevel are. We know what the differences are! I can accurately measure base bevel! Can I tell you what the actual bevel is by skiing on them..NOPE, But all I need to feel is whether they are under-beveled (too quick to the edge and less allowance for redirection) or over-beveled (too loose, need too much tipping to get on edge and drift too easily) I am not so sure about your 2 sharp, 4 dull comment! I am sure of your last statement of the prior paragraph though!!

 

[Brad J]

I switched to a .5/3 for all but my powder skis. I couldn't tell you whether it was side or base or both bevels that made the difference but I do know that I'd never go back. Whenever I buy skis I bring them to SkiMD and have Mike do a "Factory Fresh" tune and then I take it from there for regular waxing and edge touch-up.

I did the same this year with my MX74's, That tune from SKI MD.made a ski that I was ready to sell to a Fun Fun Fun zoomer groomer

 

[TheArchitect]

I did the same this year with my MX74's, That tune from SKI MD.made a ski that I was ready to sell to a Fun Fun Fun zoomer groomer

I've thought about picking up a MX74. I should really find a good end-of-season deal and do it. Of course, I also want an MX84. Decisions, decisions...

 

[Jacques]

Sometimes an old ski just has no good torsional strength left.
Then, I don't think any tune does much good to help.
Just sayin'

 

[Dave Marshak]

You don't need to do a controlled experiment...

You need a controlled experiment to show that your feelings are not just confirmation bias, but the bigger point is that I am agnostic about tall his because I never knew what angles any of my skis were tuned to, so I have no way to any feelings one way or the other. I've had good tunes and poor tunes, but I've never known what the angles were.

dm

 

[Atomicman]

You need a controlled experiment to show that your feelings are not just confirmation bias, but the bigger point is that I am agnostic about tall his because I never knew what angles any of my skis were tuned to, so I have no way to any feelings one way or the other. I've had good tunes and poor tunes, but I've never known what the angles were.

dm

Confirmation Bias my ass! This isn't the rocket science you are making it out to be! There is an instantly noticeable difference between a .5 and 1 degree base bevel unless you are a totally oblivious klutz on your skis!

 

[Atomicman]

Hey DM, do ya play tennis? I can feel a 1 lbs. difference in my string tension..........................don't need no stinkin' controlled test!

 

[oldschoolskier]

I ski 0.5 base and 4 side. Period. If you can ski balanced its no problem (if you don’t you get slammed so you better learn quickly as those friends that try my skis quickly find out). I ski my skis in all conditions and have no issues.

Best advise I can give if you want to venture down this route is master your side to side balance and edge feel (you’re overall skill set will improve).