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Bases -realistically how flat is flat?

post #1 of 9
Thread Starter 

For a start, dead flat is the optimum, but how realistic is it?  Where I am it is rare to get a ski back from a stone grind dead flat for the whole length, so what is acceptable?

 

I just got a Jr GS ski back from a stone grind that were almost dead flat over the full length when they went in, and now has a few areas (not over the full length) where it is slightly concave and where at max I can slip a 0.0015 " feeler gauge under the true bar at the center.  When looking with a light under the true bar (I use a jointer knife BTW), the gap tapers across the width and gives contact on only about 5 mm max of the base at the edges. If the shoulders were  wider (ie 15-20mm) I would just roll my eyes and move on, and accept that I need to ensure the wax is brushed out when prepping the skis. If they did not just have a fresh structure I would probably be tempted to flat file the areas in question to broaden the base contact area, and attempt to to blend them back. So should I bounce these back and have them grind more life off the ski, or not be picky and just suck it up and leave them alone as they are close enough (yes you see light under the true bar, but realistically is one and a half thou enough to make issues)? Someone else is skiing the ski, so its not something I can judge by skiing the ski.

 

Also what are peoples realistic opinions on what is the acceptable level of flatness before you should go in for a stone grind, and what you should accept back from a shop (in quantifiable terms, ie over how much of the width, shovel vs midfoot vs tail, how many thousands, over how much of the length)? Also would you differentiate between what you would accept for free skiing vs racing?

 

Thanks for the input.

post #2 of 9
Quote:
 slightly concave... When looking with a light under the true bar (I use a jointer knife BTW), the gap tapers across the width

First, get your money back.  This job was not acceptably done.

 

My test is when skiing fast and straight on firm snow.  If the ski is steady, I'm OK with it.  If the ski has a mind of its own, it needs more work.

 

I've been told that if a wide ski is flat an inch in from each edge, that's OK.  The one's I have in mind, if they had been ground completely flat would have removed way too much edge material.

post #3 of 9
Thread Starter 
Quote:
Originally Posted by SoftSnowGuy View Post
 

First, get your money back.  This job was not acceptably done.

 

My test is when skiing fast and straight on firm snow.  If the ski is steady, I'm OK with it.  If the ski has a mind of its own, it needs more work.

 

I've been told that if a wide ski is flat an inch in from each edge, that's OK.  The one's I have in mind, if they had been ground completely flat would have removed way too much edge material.

Went back to Sporting Life and they are stating that it is ok and not an issue, since they can't slip a banknote (0.0036") under their truebar.  So rounding off, their standard apparently is about 4 thousands of an inch which to me seems really big?? Next step I guess will be to test the skis on the slope. As they are not my skis, I will have to get the kid out on their old GS skis and let them compare the 2 pairs once we get a bit more coverage and it hardens up (its soft and marginal right now).

 

Will wait for the verdict, but so far not impressed, but hey that's only my opinion.

 

On a side note this was not the only issue with the tune as a side edge on both the tips and tails had not been even hit by the sharpening stone (about 3-4" at the tail and about 6" back from the contact point of the shovels (full cambered ski). Their claim was this was just cosmetic and they were sharp enough so not an issue. My opinion is the sharpness was just the burr from the base edge, and how the heck do you know what the side angle is if you have not hit the edge, even if it feels sharp? For one of the shovel edges you could even see that shine that comes off that small edge radius when you do not have a precise sharp meeting of base and side edge planes. Manager's defense of the "its just cosmetic" argument was that you do not even engage about the last 8" of a GS race ski shovel so it did not even matter, and tails should be detuned about 3" anyways, which struck me as odd and very oldschool and seems to go against what I've learned. Good news is manager relented and as a goodwill gesture had the tips and tails side edge redone and blended back.

 

On the upside, I was just having the skis done by a shop to clean up the base and rough in the edges before doing a proper hand race tune (the edges were pretty grungy), so at least I do have clean burr free edges to work with now.

 

Sigh. Maybe need to look into Ski visions base flattener...

 

Thanks

post #4 of 9
See, this is why I do my own. And yes, I shelled out for the ski visions flattener, but really only use it for structuring. I figure over time, it'll always be flattening things. Maybe some day I'll try it. I'm not racing and it's normally soft snow here, so absolute flatness is not an issue like for racing.
post #5 of 9
Quote:
Originally Posted by SoftSnowGuy View Post
 

First, get your money back.  This job was not acceptably done.

 

My test is when skiing fast and straight on firm snow.  If the ski is steady, I'm OK with it.  If the ski has a mind of its own, it needs more work.

 

I've been told that if a wide ski is flat an inch in from each edge, that's OK.  The one's I have in mind, if they had been ground completely flat would have removed way too much edge material.

 

I think the one inch from the edge rule is in regards to knowing where your edges start when skiing and also so you can sharpen your side edges.

post #6 of 9
Thread Starter 
Quote:
Originally Posted by sibhusky View Post

See, this is why I do my own. And yes, I shelled out for the ski visions flattener, but really only use it for structuring. I figure over time, it'll always be flattening things. Maybe some day I'll try it. I'm not racing and it's normally soft snow here, so absolute flatness is not an issue like for racing.


How do you find the ski visions stones for leaving fuzz vs stone grind?

post #7 of 9
Thread Starter 
Quote:
Originally Posted by L&AirC View Post
 

 

I think the one inch from the edge rule is in regards to knowing where your edges start when skiing and also so you can sharpen your side edges.


I agree as my kids had some skis that had only about 10-15mm with a significant concave center and they were a PITA to try and keep the guide tracking in the correct plane as the flat base support was so minimal. They were foam core cap skis and would be constantly be changing shape over the season. I would flat file and set base angle over and over. So glad to have moved on to traditional wood core construction. Except for the price of course:)

 

Also an issue for base edge guide especially as its base plate may track farther out where the base is still convex. A local shop likes to use snow glide type sharpener for the reason that the base plate spans across both shoulders on (most) skis if they are flat at edge but concave in middle.

post #8 of 9
Quote:
Originally Posted by CanadianQuad View Post

Quote:
Originally Posted by sibhusky View Post

See, this is why I do my own. And yes, I shelled out for the ski visions flattener, but really only use it for structuring. I figure over time, it'll always be flattening things. Maybe some day I'll try it. I'm not racing and it's normally soft snow here, so absolute flatness is not an issue like for racing.


How do you find the ski visions stones for leaving fuzz vs stone grind?

Fine. Directions here: http://www.slidewright.com/base-flattener-structuring-plane/

I'm probably scraping enough throughout the rest of the ski prep, as I'm doing hot scrapes, and several more bouts of waxing and scraping and rotobrushing after this stage so it gets taken care of.
post #9 of 9
Quote:
Originally Posted by CanadianQuad View Post
 

For a start, dead flat is the optimum, but how realistic is it?  Where I am it is rare to get a ski back from a stone grind dead flat for the whole length, so what is acceptable?

 

I just got a Jr GS ski back from a stone grind that were almost dead flat over the full length when they went in, and now has a few areas (not over the full length) where it is slightly concave and where at max I can slip a 0.0015 " feeler gauge under the true bar at the center.  When looking with a light under the true bar (I use a jointer knife BTW), the gap tapers across the width and gives contact on only about 5 mm max of the base at the edges. If the shoulders were  wider (ie 15-20mm) I would just roll my eyes and move on, and accept that I need to ensure the wax is brushed out when prepping the skis. If they did not just have a fresh structure I would probably be tempted to flat file the areas in question to broaden the base contact area, and attempt to to blend them back. So should I bounce these back and have them grind more life off the ski, or not be picky and just suck it up and leave them alone as they are close enough (yes you see light under the true bar, but realistically is one and a half thou enough to make issues)? Someone else is skiing the ski, so its not something I can judge by skiing the ski.

 

Also what are peoples realistic opinions on what is the acceptable level of flatness before you should go in for a stone grind, and what you should accept back from a shop (in quantifiable terms, ie over how much of the width, shovel vs midfoot vs tail, how many thousands, over how much of the length)? Also would you differentiate between what you would accept for free skiing vs racing?

 

Thanks for the input.


A ski needs to be reasonably flat and not prefect by any means.  As long as it is equal in both skis it will be fine.  Many skis have a slight shape to the bases.  Some a bit concave at tips and tails for instant engagement, and others the opposite for slower engagement and a funner ski.

A good skier can ski either or with good results.  Don't sweat the small stuff and work on the skier instead.


Then if you get to fed up with shops this I have found this works better than a stone grind.  I have done this many many times and all the skis run like a demon.

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EpicSki › The Barking Bear Forums › On the Snow (Skiing Forums) › Tuning, Maintenance and Repairs › Bases -realistically how flat is flat?