Beautiful grinds

[fatbob]

@GregK Thanks for the illuminating answer - somewhat more reassuring than "just trust your shop it'll be great".

So at 250 passes for a base and lets assume a structure is at least 2 passes if my base is 2mm thick I'm 2000/125=16 microns deep on each structure. If a human hair is 75 microns feels I'm out somwhere here on the maths as a structure is intuitively ast least 100 microns deep.

What am I missing or are these structures really that shallow?

 

[pchewn]

@GregK Thanks for the illuminating answer - somewhat more reassuring than "just trust your shop it'll be great".

So at 250 passes for a base and lets assume a structure is at least 2 passes if my base is 2mm thick I'm 2000/125=16 microns deep on each structure. If a human hair is 75 microns feels I'm out somwhere here on the maths as a structure is intuitively ast least 100 microns deep.

What am I missing or are these structures really that shallow?

I think they are even more thick than your calculation. Note that the originator of the "250 passes" number stopped before getting through the base So it might be 300, 400, 500 passes to get through the base.

Here's an article on surface finishes. I'd think that the surface finishes achieved for base grinds on skis is in the 1 - 5 micron range.

https://www.cnccookbook.com/surface-finish-chart-symbols-measure-calculators/

 

[pchewn]

If you read the captions of the photos at the beginning post. They are saying .02 mm for a light cut (20 micron) and .04 mm for a medium cut (40 micron). Based on those numbers a 2 mm base material will be worn out after 50 base grinds (25 years at 2 per year).

That sure is inconsistent with the 250 passes and not through the base ....

 

[GregK]

@GregK Thanks for the illuminating answer - somewhat more reassuring than "just trust your shop it'll be great".

So at 250 passes for a base and lets assume a structure is at least 2 passes if my base is 2mm thick I'm 2000/125=16 microns deep on each structure. If a human hair is 75 microns feels I'm out somwhere here on the maths as a structure is intuitively ast least 100 microns deep.

What am I missing or are these structures really that shallow?

The 250 passes were on a flat belt or passes on a stone in the “pre structure/get it flat” stages would be not be taking off much per pass compared to the structure passes which would vary in depth depending on the structure. Even the flat passes can vary depending on speed across the stone and pressure applied from the machine.

The pics above show one structure that is .04mm in depth and one that’s .02 in depth. The deeper one would be for wetter, warmer snow conditions I assume and the other for more speed in colder conditions. Factory “universal” structure would be in the even lighter in depth.

 

[fatbob]

Doh should have gone back to the original post. But my crude rationalisation broadly proves for a shallow structure at 20 microns. I get plenty out of a base.

Just have to find a shop with a good autofeed.

 

[Noodler]

I may get some better info on grind types on Friday. I dropped off my skis at the Denver Sports Lab and had an interesting discussion with Lee (one of the co-owners). I showed him some of the grind pics and we discussed what might work best for the skis I was dropping off. He said that he likes to "test" the base material to see which of the grinds would be best for the skis. I dropped off a 92mm all-mountain ski and a 68mm groomer zoomer. I left it up to him to decide what he wants to do with them. So Friday should be fun to see what he decided would work best. He said that we can discuss it more in-depth when I pick up the skis.

 

[Tricia]

I know the pattern of a base grind makes a big difference in how the ski performs.
While looking for an image of the AM Bell Grind from @smoothrides I stumbled upon some images from their FB page and I needed to share these here.

Aren't they beautiful?


View attachment 82052
Grind of the day: AM Bell. We use this wave class grind for most recreational skis in Tahoe. It runs well in a variety of conditions, and is cut as a margin just narrower than the waist of the ski.

View attachment 82053
Grind of the day. We use this grind for SG skis in typical Tahoe conditions. Even though the structure is very clear, it's actually a medium depth of cut at .04mm. The lower pitch helps to move water quickly at higher speeds, and the margin allows us to run a true .7 base bevel without any structure in the edge.

View attachment 82054
Grind of the day. We use our Tech Wave on most SL and GS race skis. This is also a multi layer structure, with a very fine, high pitch base and a margin wave running slightly narrower than the waist that carries through the tip and tail. It's a center specific structure and a very light cut at 0.02mm. This makes it work extremely well for lots of turning and side to side motion. Even though this pattern is very clear, the real speed in this grind is the micro structure below, which is virtually impossible to capture with the camera. Photo taken straight off the stone grinder before wax or edge prep.

The pics above show one structure that is .04mm in depth and one that’s .02 in depth. The deeper one would be for wetter, warmer snow conditions I assume and the other for more speed in colder conditions. Factory “universal” structure would be in the even lighter in depth.

Thank you for the added information.

The first picture of a grind is the AM Bell, which is what we tend to get on our test skis, especially for spring snow.
From what I gather, its desired affect is to handle wet snow better and not get sucked to the surface.

I'm guessing, (and I'll ask Coop when I see him) that the other two skis are not as deep.

 

[mountainwest]

Thanks for sharing these base grind photos & descriptions, Tricia! I'm going to pay more attention to what kinds of grinds my local shop does this season and now I will have some clue of what I'm talking about.

 

[pchewn]

Here's some pictures from the Wintersteiger brochure ..... Their brochure says:

"The structure package gives you the option of creating and applying an unlimited variety of structures. The package includes a high-performance dressing unit, which is also used on the Race NC, the racing service flagship machine by WINTERSTEIGER. In addition to this, the optimized centering system ensures easier handling, even for center specific structures."

The brochure also says the depth of the grind can be adjusted in increments of .01 mm (10 microns).

 

[Toddski13]

This is a great discussion and one that doesn’t happen enough.

Right away, it’s critically important to clarify something from the OP - the cut depths that are stated are actually the diamond advance depths set before dressing the pattern into the stone. It’s a common misconception that this advance or depth is the biggest variable or has the largest impact on actual structure depth when the ski is ground.

You can see the attached matrix and understand that there are a lot of variables that need to be accounted for in both the dressing phase of the process (cutting the structure onto the stone) and the grinding phase (imparting structure, whether it’s a rough linear to flatten skis or a beautiful thumbprint finish structure).

In fact, the diamond dresser travel speed relative to stone rpm during the dressing process has the largest impact on both structure depth as well as structure width. From there, grinding pressure has the second largest impact. After that, diamond advance rounds things out.

Circling back to the discussion of how many times a ski/snowboard can be ground or how many passes over the stone can be done before grinding through, there is no clear cut answer. The condition of a ski when it comes in to the shop ultimately dictates what will be required to achieve a flat base, but beyond that things like thickness of base material from the factory and construction play a big role in determining whether a ski can ever be ground flat or if it can be flattened five or six times over several seasons.

Examples of challenges here range from the crazy deep structure that Fischer used to press (not cut) into their race skis to Rossignol Classic 70 and 80 skis from ten years ago that had paper thin bases to modern, wide, twintip rocker skis that are torsionally wobbly enough that getting them truly flat, especially in the tip or tail is near impossible.

At the end of the day, a good shop with an experienced tech can evaluate your skis using their eyes and a true bar to give you an idea of what’s possible. Skis that have been serviced to a point where more flattening is risky can still have things like core shots repaired by gently running the ski to integrate the repair with the adjacent base material.

I can put together some images of specific grinds and their applications... remember that grinds are like tires on a race car - you want something universal at a minimum. That said, flat skis with proper bevels are going to be consistent and predictable in all conditions which can be a huge plus for those of us just trying to enjoy ourselves.

 

[Toddski13]

I may get some better info on grind types on Friday. I dropped off my skis at the Denver Sports Lab and had an interesting discussion with Lee (one of the co-owners). I showed him some of the grind pics and we discussed what might work best for the skis I was dropping off. He said that he likes to "test" the base material to see which of the grinds would be best for the skis. I dropped off a 92mm all-mountain ski and a 68mm groomer zoomer. I left it up to him to decide what he wants to do with them. So Friday should be fun to see what he decided would work best. He said that we can discuss it more in-depth when I pick up the skis.

What did you end up with? Any insight as to how he ‘tested’ the base material?

 

[pete]

What did you end up with? Any insight as to how he ‘tested’ the base material?

@Noodler ... ?

I just ran across this thread ... very interesting.

 

[Noodler]

@Noodler ... ?

I just ran across this thread ... very interesting.

I don't recall ever learning exactly what they did to determine what structure pattern to apply to the ski. Honestly, looking back on this discussion, I find it odd that the base condition would have any impact on the pattern selected. Doesn't add up for me. However, I'll have another chance to discuss this with them as I'm bringing another batch of skis there for more grinds.

 

[Erik Timmerman]

OK so I'll ask, after a terrible experience with a snowboard decades ago where the shop totally took about 5 years off the lifespan of the board by overgrinding I've totally sworn off shop grinds unless my bases are totally FUBAR'd without.

How much life does each of these structural grinds take off the skis - if you restrutured say twice annually how many years would an average retail ski last (assuming no other wear n tear - appreciate that heavy rental stock designed to be butchered my last longer, an FIS base shorter)

@Mike Thomas has a story about the shop manager in shop he used to work at in NH who would tune his skis literally every time he skied. He'd go skiing, then come back into the shop and be like "tune these skis", so the skis would get like 30 grinds a year and they were fine. So my answer is if the shop is any good, din't worry about it.

 

[Erik Timmerman]

I wonder if you can really tell one grind from another in pictures. Is there stuff we just can't see?

 

[KevinF]

@Mike Thomas has a story about the shop manager in shop he used to work at in NH who would tune his skis literally every time he skied. He'd go skiing, then come back into the shop and be like "tune these skis", so the skis would get like 30 grinds a year and they were fine. So my answer is if the shop is any good, din't worry about it.

Stone grinding the skis every time out? How often does your daughter get her race skis ground?

Before I had any idea about tuning terminology, I would get my skis stone ground more often -- i.e., 2, 3 times a year. I'm lucky enough to have SkiMD in my backyard (i.e., a really good tuning shop), but yeah -- skis seem to be capable of taking more stone grinds than is regularly thought. Even with that frequency, I'd get a three, four years out of a pair of skis.

 

[Erik Timmerman]

Stone grinding the skis every time out? How often does your daughter get her race skis ground?

Two to three times per year. Maybe should do it a little more. You can lose that base bevel without really knowing it. I'm not made of money though. Obviously grinding every time is way beyond excessive, and I think would actually be detrimental to performance, but it won't wear out your skis.

 

[Dakine]

How did we ever get around in the old days with no grinds and infrequent, rub on waxing?
Oh wait, that's just the ticket for cold, dry snow.

 

[Uncle-A]

It is no doubt we have an extreme number of high performance skiers here in the community. But for the other 90% of the skiers out there, can they really feel the difference between a different type of grind?

 

[Erik Timmerman]

It is no doubt we have an extreme number of high performance skiers here in the community. But for the other 90% of the skiers out there, can they really feel the difference between a different type of grind?

YES! I don't know that they could tell the difference between good and great, but definitely bad from good. They wouldn't know that's what they are feeling, but they'd feel it.