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Stone Grinding Base High Skis

post #1 of 14
Thread Starter 

  Today I found myself with a bit of a challenge, decided to document it as best as possible, and share it with the gang here on epicski. I will omit a few details, partly to keep this post short, and also to protect some proprietary knowledge. :)  What I have is a pair of '14 Head GS 195 r35m RS skis that are severely base-high.  My definition of base-high is that - with the ski on a bench base side up, the base is higher than the edges. These skis were used this summer/fall in pre-season training camps on glaciers.  The nature of this base/edge profile is due to excessive base edge filing, and/or abrasion.  You can also note that there is no structure left on the ski, as it originally had a cross-linear pattern.  The challenge lies in that I need to grind this ski flat, setting the base edge bevel to 0 degrees, reset the base edge to .5 degrees, and imprint a structure - without grinding through the ski.

 

 

 

I am using a Montana Snow Cruiser (robotic tuner) to process these skis.  Montana and Wintersteiger have slightly different variations with regards to how they process equipment.  Some people say that the operation of robotic ski tuning equipment doesn't require very much skill.  That could be partly true, but to do what I am doing here requires an operator that knows how to identify the processes being done, which programs to use (in order) and, when/how long to use the appropriate amount of processing, in 3 or more programs.

 

That said, the first thing I did was grind the ski on a "pre-grind" or "rough-grind" structure.  The goal is to return the base to flatness, and the base edge to 0 degrees.  You will notice that these skis have factory installed base burn ptex strips along the edges in the waist area of the ski.

 

 

Pre-grind base flattened, and base edge set to 0 degrees.

 

 

Top-view of pre-grind structure

 

 

Next is to erase the pre-grind strucure from the ski, and the stone with what is sometimes called a "mirror grind"

 

And finally time to imprint a cross-linear pattern, as well resetting edges to .5 base and 3 side.

 

Top view of final structure.

 

So in a nutshell thats it!  I hope you guys enjoyed this post, and as always, feel free to post any comments or criticisms.

 

Pray for Snow!  :beercheer: 


Edited by Chenzo - 10/16/13 at 7:18pm
post #2 of 14

Nice work!
How much material did you scrape off? and what's with the base burn ptex? :confused

post #3 of 14
Thread Starter 
Quote:
Originally Posted by jzamp View Post
 

Nice work!
How much material did you scrape off? and what's with the base burn ptex? :confused

When you say scrape, do you mean a steel scraper?  I did not use a steel scraper, just the stone grinder.  Or do you mean how much material was removed?  I can only estimate that 1/4 to 1/2 of the base thickness was ground away.  If you look closely at the gap between the edge and the true bar in the first image, that will give you an idea of how much material was removed.

 

Base burn ptex is technically not the correct name for this, I believe Atomic calls them base inserts.

 

From Tognar's website - 

 

Quote:
 Some Atomic alpine race skis feature narrow strips of ceramic base material inlaid along the steel edges. This is done to help avoid base burn, since ceramic is harder and more durable than p-tex.
You can tune, patch and wax these areas just as you do the rest of your base without a problem.
post #4 of 14

yes by scraped i meant removed with the grinder; if you removed as much as 1/2 of the base how many grinding cycles do you think are left in the skis?
As for the base inserts, that's interesting! I had never noticed them...
 

Thanks!

post #5 of 14

Ouch, that was a lot of base to take down.  Be careful waxing and hot boxing.  If the p-tex is too thin it can bubble under heat.

 

I had a pair of skis I let get that convex many years ago.  When I flattened them out again I could see the spines from the edges under them, but it was clear p-tex so they were still actually skiable.  Nice work.  More runs on flat is better than more runs on noodly rounds.

post #6 of 14
Thread Starter 
Quote:
Originally Posted by jzamp View Post
 

yes by scraped i meant removed with the grinder; if you removed as much as 1/2 of the base how many grinding cycles do you think are left in the skis?
As for the base inserts, that's interesting! I had never noticed them...
 

Thanks!

On this particular ski, if the base edge wasn't subsequently over bevelled with a file, I could imprint this structure probably 3 more times.

 

Quote:
Originally Posted by crgildart View Post
 

Ouch, that was a lot of base to take down.  Be careful waxing and hot boxing.  If the p-tex is too thin it can bubble under heat.

 

I had a pair of skis I let get that convex many years ago.  When I flattened them out again I could see the spines from the edges under them, but it was clear p-tex so they were still actually skiable.  Nice work.  More runs on flat is better than more runs on noodly rounds.

Ya I have a ski in my graveyard that was ground very thin, and when waxed the base delamed near the edge.  I looked for it today to take a pic, but I couldn't find it.

post #7 of 14
Thread Starter 

So today I am documenting a different example of a base-high profile.  This is a brand new pair of 2013 Rossignol gs 182cm r23m RS skis that I worked on today.  They were factory tuned with wintersteiger equipment.  I measured the base edge bevel to be at 1 degree, possibly a little more.  I am stone grinding them, and resetting the base edge to .5 and the side to 3.  

 

The main reason for tuning is that the edge is below the base - this is sometimes referred to as a relieved edge.  This may work for speed skis, but it is not ideal for a tech race ski.  Unlike the convex profile on the head ski in my first post, the bases on this rossi are relatively flat, with a little concavity in the tip an tail areas.  The goal of grinding this ski is to process a flat edge to edge profile on the base, with a .5 bevel.

 

This is the "Before" shot of the factory tune.  These next two pics are organized with shots of the tip area at the top of the shot, boot center next, and tail area at the bottom of the image.  Note the gap between the true bar and the edge.

 

 

This next pic is after I stone ground flat, imprinted new structure, and reset base edge bevel to .5 degrees.

A gifted stone grind artist can perform this on an older manual fed machine.  But those tech's are few and far between.  For perfect consistency, a semi-automated or fully automated machine operated by a well trained tech, will result in optimum results with regards to the base and edge profile.  

post #8 of 14
thats nice work, chenzo! funny how messed up new skis can be...and how most people dont even realize it....

zenny
post #9 of 14

They used to ship all new skis a little base high cause they came in stacks and didn't wan them damaging the skis under them in the stack.

post #10 of 14
Thread Starter 

thanks Zenny, ya here in the east most people don't realize how important it is to have a flat base edge to edge - that is until they ski it.

post #11 of 14

Chenzo,

 

On your first ski, you said you took off 1/4 to 1/2 half the base thickness. Did you really mean you ground away 1/2 of say .100 inches. That is a whole lot of grinding. I am assuming the bases are .060 to .100 inches thick. It looks like you needed to take off about .005 to .010 inches to get everything flat again. A 1 degree bevel is .003 inches lower than the base height, so if you were getting a flat base back to 0 bevel, you would take off .005 inches. I am sure the machine can do it, but my untrained eye says you needed to remove about .010 inches. Did you measure how much you took off? I would think you would just keep taking passes until the true bar told you it was flat?

 

Nice work, the ski looks great. Did you base bevel by hand or does your machine do it for you? I am planning to take about 10 pairs of skis back to 0 base bevel and I am debating how to do it.

 

Scott

post #12 of 14
Thread Starter 
Quote:
Originally Posted by bttocs View Post
 

Chenzo,

 

On your first ski, you said you took off 1/4 to 1/2 half the base thickness. Did you really mean you ground away 1/2 of say .100 inches. That is a whole lot of grinding. I am assuming the bases are .060 to .100 inches thick. It looks like you needed to take off about .005 to .010 inches to get everything flat again. A 1 degree bevel is .003 inches lower than the base height, so if you were getting a flat base back to 0 bevel, you would take off .005 inches. I am sure the machine can do it, but my untrained eye says you needed to remove about .010 inches. Did you measure how much you took off? I would think you would just keep taking passes until the true bar told you it was flat?

 

Nice work, the ski looks great. Did you base bevel by hand or does your machine do it for you? I am planning to take about 10 pairs of skis back to 0 base bevel and I am debating how to do it.

 

Scott

Very nice observation !!  

 

Common base thickness on race skis (new, unground) is 1.2 mm / .047".  The exact dimensions and type of raw materials is proprietary, and varies with the manufacturer - so 1.2mm is an educated guess as to the original thickness of the base on most new race skis.  By the time the ski leaves the factory, thickness is less than that.

 

I did not take any measurements on this ski.

 

How I determined that I ground 1/4 to 1/2 of the ski is by:

- the amount of passes on pre-grind (rough grind), which was 48.  4 series of 12 passes, with true bar measurement and alternating the pair of skis (left to right, right to left, etc.)

- the amount of base material left in the fresh sheet of filter paper. (I use a new sheet of paper for every problematic grind)

- but most obvious is by looking at the edge thickness, and comparing it with an exact new model - see next pic.  (although one doesn't need to compare to identify a thin edge)

 

This is a pic of two exact same, brand new, out of the wrapper,  fis gs skis (two pair, one of each) that have relatively the same edge to edge profile, and base edge bevels.  One of these has been obviously overground by the factory.  I slotted a piece of paper in between to help illustrate the difference in edge thickness, which is more noticable on the left side of the image.  Theres a shadow from the paper on the right side of the image due to the paper overhanging from the sidecut.  Not the best picture, but the top ski has a thinner edge than the bottom.

 

Our machine is mostly meticulously maintained.  I have good confidence in our HTT system to apply accurate base bevels.  I also feel that the HTT is the best mechanical means of processing the base edge, when compared to wintersteiger.  In season we personally test our bevels on snow every week, when we are in season.  I really enjoy setting b/e bevels by hand, but to be honest I rarely perform this these days.  We are just too busy.  (Just did 35 new ski race preps - ground flat, structure imprint, reset bevels, hand finishing and waxing/hotboxing this past 5 days)  But when I do a hand base bevel, it is usually for a ski that requires a variable bevel.

 

But I would say to you is that you should do your base bevels by hand yourself - ten pairs is a lot, but it would be way more gratifying, and you would have total control of your tuning.  Base edge is the chassis of the ski, and is very important imo.

 

word

post #13 of 14

Impressive, bases are thinner than I thought.

post #14 of 14

Good stuff.Good information. Thanks for posting it. In my experience, the depth, or thickness of the side edge is without doubt the best indicator of how much base depth the ski has left. My kids are both former NCAA/NorAm skiers, and I've always been surprised how much base the skis fresh from the factory tended to have....with their two companies. And, upon occasion they arrived as Chenzo described....very thin, overground. But that was the exception to the norm. I've also found for whatever reason that the "visible spine" of the edge through the base, even when waxing at real low temps is more pronounced with some race skis than others. Even new ones with a single light grind. Not sure why. Has never affected anything to do with the performance of the ski, or life of the ski.  I've also had a tech on occasion say "I'm not sure if we have another grind left in these", and we've gone ahead....without blowing through the base. Though I have seen other skis ruined by "one more grind" done by the wrong guy on the wrong machine. Guys who are very experienced with their "machines", like Chenzo, can work a lot of magic with a light touch. The new kid in a shop with older out of tune equipment can do a ton of damage. I think that asking questions, like "do you do a lot of race grinds?", and "can I look at a race ski that you're re-ground, and applied a structure to?" will help. I know that the tuner/techs who I've worked with are very proud to show of their work, and talk and share opinions and thoughts, as long as it's not the time of the day and week when it's a frenzy in shop, activity-wise. 

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