Edge Tuning Geometry

[Eboot]

I have long been confused by the need to add a base angle when tuning edges.

Assumption: edges less than 90 deg are sharper than edges greater than 90 deg.

Below is a screenshot taken of a base tuning tool that confirmed for me what I thought was happening:

Below is a diagram of the geometries as I understand them:

 

So in my mind:

• adding a base angle makes the edge less sharp
• adding a side angle makes the edge sharper

What am I missing: why add a base angle?
 

[Corey]

Less edge catching when riding flat. Don't forget that the rear half of your board tapers the other way, so the edges eager to grab. 

[Eboot]

7 minutes ago, Corey said:

Less edge catching when riding flat. Don't forget that the rear half of your board tapers the other way, so the edges eager to grab

That makes sense but implies that you are detuning it and not making it sharper for ice (for example)?

[SunSurfer]

"Sharper" is an interesting concept. You can have a knife blade, angle between the 2 faces maybe 3-4 degrees for a good chef's knife yet if it is blunt it still won't cut as it should, and can if properly sharpened. So angles aren't everything.

A new Coiler Nirvana altered my ideas about this a little. I asked BV what angles it came with. 89 side, 0 on the base. I tried riding it without making any alterations to the tune. It carved beautifully, and edge catches on cat tracks were a non-problem for me. In time however the edge hold got a little less secure on hard pack. I assume, because I didn't get out a microscope to look, that my 89 degree edge was now rounded rather than an abrupt change from one steel face to the other.

[daveo]

0deg base edge angles can be super catchy when riding flat. Many years ago on my old Coiler, it caught me out a few times before I realised what was happening.

If you want it 'sharper', you can just increase the side angle.

[Mr.E]

Its pretty rare to add base bevel and leave the side at 90*. Adding say 1* base and relieving the side 2* gives an included angle of 89*. 

Ultimate sharpness has to do with how keenly these bevels meet, but even a "dull" 1*base with side bevel can give improved grip without base flat catchiness.

That said, not everyone tunes the same way, and not everyone has the same feel preferences, so experiment if you want to see what works for you.

Edited March 15, 2022 by Mr.E

[Odd Job]

Also, metal is slower than p-tex.

I mean if that matters, surely doesn't matter to me.

I ride 0.5 base and 3 side; so an 87.5 degree edge.

[Aracan]

i ride what is probably the most usual tune: 88° lateral and 1° base, which, as the OP correctly states, results in a slightly acute angle. I never have problems with edge catching, and the grip is good.

[st_lupo]

I've got 0 deg base bevel on my Nirvanas and .5 deg on my other boards.  88 deg tunes on all of the sides.  The base bevel is just a matter of preference, if your board isn't super catchy, you don't need it (ref the Nirvanas with early rise tips/tails).  My Kessler has a .5 deg base bevel (I don't think it was necessary but it was already on when I got it used) and _maybe_ that has something to due with my impression that its handling is vague at slow speeds.  If you tend to do jumps (especially rotational) and are not keeping the board on edge all the time you would probably benefit from some base bevel.  Once you have a base bevel on, it isn't coming off without a base grind.

The sharper the side-tune the more it will need touching up and will impact longevity.  88deg on the side hits a good balance for my local riding conditions (generally firm to hard man-made snow) and I don't detune the tip/tail. 

Just keep in mind that sharper edges are no replacement for board angulation!

[Corey]

Another benefit of a slight base bevel: Less material removal to sharpen edges. 

At a true theoretical zero degrees, in order to sharpen the bottom face of the edge you need to remove material from the entire width of the board. At even a small angle, you end up removing mostly steel when sharpening and barely touch the Ptex. 

I tried 0.5 degrees base bevel and found it almost as frustrating as zero. 1 degree base and 88 side was a nice balance. 

With all the bumps and curves that occur in the snow we ride on, I do question how much of this is placebo and how much is real. 1 degree of bevel across a steel edge amounts to a few thousandths of an inch of height difference from the base level while we ride over 1/4" ridges without noticing them. 

Use the angles that make you feel the most confident and you'll probably ride better for it. 

[VSR-Alex]

55 minutes ago, Corey said:

Use the angles that make you feel the most confident and you'll probably ride better for it. 

This.

I tend to try to get as close to 0 degree base as possible with either an 87 or 86 degree edge bevel.
My only purpose for adding a base bevel is to only bevel as much as the base grind technician is comfortable with so they don't ruin their structuring stone, so the base is not edge-high, and so the base edge doesn't end up with the structure in it.

Again, this is all personal preference; I am usually never flat base anyway.
I just hate the slippery-slidey feeling of a big base bevel at low edge angles.
I suppose it also depends on the snow texture too, soft vs hard snow.

[Eboot]

Thanx all - my underlying assumption that base bevel was intended to help with the effective edge angle was flawed. Great input as usual from all - much appreciated.

[TimW]

I agree with Corey, I think it is mostly placebo, I never truly noticed a difference. But I do it for the ease of tuning.

I also made this for lazy sharpening of edges. Mini grinder with 56mm diamond grinding wheel. Seems to works nicely, let's see how the wheel holds up.

Now only for the edge, maybe I will modify it so it can also do the base bevel.

Edited March 15, 2022 by TimW

[st_lupo]

20 hours ago, Corey said:

Another benefit of a slight base bevel: Less material removal to sharpen edges. 

At a true theoretical zero degrees, in order to sharpen the bottom face of the edge you need to remove material from the entire width of the board. At even a small angle, you end up removing mostly steel when sharpening and barely touch the Ptex. 

I tried 0.5 degrees base bevel and found it almost as frustrating as zero. 1 degree base and 88 side was a nice balance. 

With all the bumps and curves that occur in the snow we ride on, I do question how much of this is placebo and how much is real. 1 degree of bevel across a steel edge amounts to a few thousandths of an inch of height difference from the base level while we ride over 1/4" ridges without noticing them. 

Use the angles that make you feel the most confident and you'll probably ride better for it. 

Wait... you guys sharpen the base bevel more than once?

[Corey]

7 hours ago, st_lupo said:

Wait... you guys sharpen the base bevel more than once?

Only after adjusting the edge profile with rocks. 

I do hit it with fine stones every year or two. 

[daveo]

9 hours ago, st_lupo said:

Wait... you guys sharpen the base bevel more than once?

Nope. After a base grind, sure.

Edited March 16, 2022 by daveo

[st_lupo]

1 hour ago, daveo said:

Nope. After a base grind, sure.

 

[lowrider]

I do not think Bruce has used up his supply of edge stock but if what I see in the thickness of edge stock used in new skis there does not seem to be a lot of material to play with either bottom or side.

[Mr.E]

We're talking .5*-3* at the regular extremes. Even on 1.7mm edge stock thats not much material removal.

 

[scottishsurfer]

I'm 0 base 87 degree side kind of guy it is catchy but you get used to it and i feel(most likely placebo) that edge engagement is more definte and performance dealing with Ice is better than having a slight bevel. I wouldnt  reccomend it for most people if im honest but its largely a personal preference thing.

[VSR-Alex]

17 minutes ago, scottishsurfer said:

I'm 0 base 87 degree side kind of guy it is catchy but you get used to it

When I was a beginner learning how to carve higher edge angles on my Donek Incline, I used to rely on catching the edge on purpose to help transition between turns...