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Concave Ski Bases???

post #1 of 24
Thread Starter 
I was waxing my new Atomic 9.18's and noticed during the scraping stage that i couldnt even touch the wax running along the center of the base all the way from tip to tail, especially in the wider area at the shovel and tail. I couldnt scrape it until I grabbed the edges of the wax scraper and pushed into the center slightly to give it a "reverse camber " to fit down inside to scrape it. After brushing and skiing the skis worked fine as near as I could tell, but it keeps nagging me that they are like that. Is that something intentional or accidental? Will a stone grinding flatten that out and if so is it something that will beneficial to my skiing? Lastly, if that is somethiug I should leave alone, are there slightly curved scrapers I can use to kinda speed things up?

Thanx in advance

post #2 of 24
Karsten - I have no solid confirmation of this, but heard last season from a couple tuners that this is not uncommon for Atomic. And it is a flaw in their manufacturing process.

Not sure if that helps you at all - but may give you a stronger lean toward determining them defective.

Good luck.
post #3 of 24
your bases are most likely to be concave. Concave bases will result in your skis getting stuck going straight down the hill, which will make it harder to slalom your feet back and forth.(convex bases will wiggle all around, making it hard to control) soo, you need a good grind. Go for a stone grind- much better for your skis than a belt grind. A good stone grind and re-une should cost beween $30-50. there isn't a need and I don't even think there is such a thing as a "convex" scraper(anyway flexing it does the same thing).

post #4 of 24
eh... not too big of a problem when you compare it to decambering skis... haha.
post #5 of 24

I am almost 100% certain that they are supposed to be concave. I have two pair of Atomics and they also are that way. I would have your ski shop contact Atomic to be sure and I would make sure that the shop techs know the next time you bring them in for a tune. While you're at it you may also make sure they know what your edge bevels are supposed to be (unless you want them different). Atomic is a little weird that way too. Good Luck.

post #6 of 24
Have the skis stone ground and tuned by a reputable shop.


[ December 12, 2002, 08:03 PM: Message edited by: Maddog1959 ]
post #7 of 24
we were sternly warned by our atomic rep that atomics are supposed to be concave...if this is to coverup the flaw or if it's actually the case, i can't say...but, here's what i do when tuning atomic skis.

if someone needs a stone grind, lower the pressure on the feedwheel and also increase the clearance between the feed wheel and stone. This allows for edge high skis to be stone ground as well without damaging the stone badly.

They ARE a pain in the ass to wax and scrape...but get a good ski, you make sacrifices [img]smile.gif[/img] (or that's what they want you to believe). I'd say sell the atomics and get volkls [img]graemlins/evilgrin.gif[/img]

as for waxing...not much to do except put pressure in the center of the scraper...OR, you can try the crayon waxing method in which case there's not so much wax on the base that can't be dealt with a scotchbrite pad and a good horsehair brush to finish up. That's the method of choice for me when i'm doing wax jobs for ppl at the shop.
1. rub the wax on
2. iron
3. buff with scotch brite (requires a little more elbow grease than after scraping)
4. brush with horsehair brush
it's very fast, so i take the extra time i have left sometimes to sprinkle some flouro powder and cork it in

hope this helps [img]smile.gif[/img]

post #8 of 24
You'll often get a little teardrop shaped slightly concave section at the shovel of beta construction skis. It's pretty minor and the race room guys say it's not a worry as long as the ski skis fine. The last thing you want to do is base grind them until you get rid of it, you'll take way too much base off. I skied my new Atomics today right out of the box and they were great. I'm guessing they'll have the little concave spot as well.
post #9 of 24
Leave them alone like L7 says , he's right.......although he may not know much about women he knows skis!!!!
post #10 of 24
Here is my understanding but I am not an expert so keep that in mind. Betaracer would be the authority on this.

All beta skis are concave by design. If you put pressure on the top of the ski, it flattens out (therefore it runs flat while skiing). This is the nature of the design of the dual cores running along the edges of the ski. If the bases are ground without the proper pressure and you flatten the surface, then the base would actually run convex when you are skiing, not a good thing (you would spoil your racing skis). I have found that some Atomic dealers recommend flattening it out, while the finer shops here at Tahoe say absolutely no, and that it is not a problem to do it properly. I will try to find out about the waxing technique.
post #11 of 24
Originally posted by Leeroy:
Leave them alone like L7 says , he's right.......although he may not know much about women he knows skis!!!!
I know I should know who Leeroy is but now I can't remember. Damn
post #12 of 24
My Beta Atomics are concave in a 5 inch area of the shovel. Flat everywhere else though.
post #13 of 24
I had my atomics flattened by a rather unreputable shop, and one of them seems to have some wobble to it(very annoying) so you think that its convex now??? maybe betaracer can help me...

post #14 of 24
I once asked the same question in this forum and received a a number of responses both pro and con on the subject of Atomic skis although my question related to shaped skis generally. You can look up the various threads on the subject using the search feature.

Tognar Toolworks says that the problems with concave shovels and tails are a consequance of these areas being wider than was the case with conventional skis and more prone to becoming concave during the curing process. The issue is not confined to Atomic skis only. Atomic reps and their defenders maintain that's how they are supposed to be and were designed that way. On this issue I find Tognar and others here more persuasive.

Tognar in its catalogue argues against trying to get the tips and tails completely flat as it takes down too much of a skis edges, and P-Tex shortening the skis life. They recommend getting the bases flat at least 3/8th inches from the edges leaving a smaller concave area in the center.
post #15 of 24
Thread Starter 
wow thanks alot,
so many responses, since they ski well, and the advice I recieved here, I think I'll just let them go.
post #16 of 24
Good move Karsten. Atomics are well-made skis
post #17 of 24
I was always under the impression bases went a little concave after they have been skied for a while, the p-tex naturally wearing down quicker than the steel edges. Although this concavity would only be slight unless left for a long time?
post #18 of 24
Just out of the shrink wrap my 11.20's were slightly concave for a few inches from the shovel, then one ski was noticably convex from that point to just ahead of the toe piece. I flattened the base high section and left the concave area alone because it was close to being flat. The rest of both skis were flat. They ski just fine. The Atomic rep that I spoke to when I bought them said that they are supposed to be flat, but because of the width in the tip and tail the shrinkage during curing may cause them to be a little concave in those areas, which shouldn't affect their skiability. I've also seen this with other brands, so its not unique to Atomic. My skis usually become a little convex with wear, rather than concave. Don't know if this will be the case with the Atomics.

post #19 of 24
Thread Starter 
Realized my first real down-side to the concave bases, I tried to crayon on the wax before ironing and its a no-go on the shovel and tail, iron wouldn't even graze it. Guess I'll have to go back to hot dripping and then ironing (*sigh* the waste!). Not a huge prob though.
post #20 of 24
Both of my Atomic 10.ex's are slightly concave and they ski great, wouldn't trade them for anything.

Betaracer (our Atomic expert) has explained this previously. You can do a seatch to get the full discussions, but here are the highlights:

Originally posted by Betaracer (over a year ago):
The concavity of the bases is common among all models in the Atomic line. Even though there is this trait, they ski right from the factory can be skied and waxed (for the most part).

Every Demo I do someone complains that their new skis don't ski like the Demos that they loved so much. Either they had a 'grind' done, and/or they used non-Atomic bindings. I haven't had a machine touch my skis since they left the factory this season. It is the absolute last resort to tuning, and I will have a Ceramic Edge refinish done after, at factory angles.

Like Scotchguard and Velcro, many a good thing came from mistakes. The same with the concave base. Since all skis, no matter which brand, have tosional flex, Atomic's thought was that since the concave skis flatten with very little force, this will reduce the overall torional flex while skiing.

Originally posted by Betaracer (over a year ago):
You have the ski, which is a mostly flat structure. Now, relate that shape to a leaf spring on a truck. The spring has a bend in it, and as the ends are flexed in a direction to make the spring straighten, it gets harder and harder to move, making an vary stiff piece of metal. With the Atomic concavity, this principle occurs. Instead of having a straight ski, and having it flex convex under more pressure, the Atomic ski becomes more rigid as the it becomes flat. I don't think this can be explained in any simpler terms.
post #21 of 24
AC, I respect your experience with your Atomic ski's but there are others with different takes on concave bases in at least some skis:

In relevant part by Tog in a previous thread:

Quote: The idea that the ski base is supposed to be concave and it flattens out is ridiculous. I'm remember beta racer's comments on this and they just don't make any sense. He compared it to a leaf spring but a leaf spring is supported at both ends. Also there was a claim that Atomic invests millions in finishing equipment. Well Ford invests billions in car plants, does that mean their cars are perfect?
Fact is skis are "finished" before they're really ready to be. It just is not practical for manufacturers to store skis and then finish them when the glues have stabilized.
What's interesting is that they ski well with somewhat concave bases.
I'll post here the answer I got from someone who has a shop and tunes a lot of atomic skis for national level races too:

A concave base will not ski as well as a flat base. This is more pronounced
in firmer snow that is grippable than in soft snow where the ski does not
get a firm bite. Most manufacturers have difficulty delivering a finely
tuned product to the consumer for several reasons:
1 - Resins used in ski manufacturing tend to cure for some time after the
ski is produced which can cause a ski to take on an irregular shape. It is
simply not practical for the manufacturer to set unfinished skis aside for
several weeks for curing before doing the final grinding to flatten the
2 - Finishing processes at the factory level are entirely by machines which
change during production runs. Machines must be constantly "dialed in" as
their abrasive drums or discs wear away. Different sidecuts and sizes
(thickness and length) also require changing setting on the machines to
deliver some degree of uniformity.

Atomic tends to ship concave skis. This is probably because the Beta shape
with the higher humps tend to put more pressure in the center of the ski
when the ski is fed through a grinding machine with a pressure wheel on top
of the ski. Their base edge bevels also are quite erratic as they
consistently vary between 0°- 3°. I believe this is caused because the
automatic bevel machine cannot grind the edge where the ski base has any tip
curvature. Therefore, the skis usually have no bevel in the extreme forward
contact point and then tend to pick up a 3° "divot" immediately after the
bevel machine makes contact with the ski.

Our solutions:
1 - "If it ain't broke, don't fix it." Many "imperfect" skis perform quite
well depending on the skier and snow conditions.

2 - Make certain the base bevel is at least 1° with a guide,
file and polishing stone. Don't worry about slight irregularities of
increased base bevel unless you feel performance is being compromised.

3 - Erratic behaving skis are ground to somewhat flatten the tip area. We
grind with only hand pressure on the ski to eliminate the concavity caused
by the feed wheel putting pressure on the center of the ski. We consider
the ski to be flat when it is flat about 25% in from each side. A slight
tunnel in the center does not have any adverse effect. We then use guides and
hand tools to establish 1° base and 3° side bevels. Edges are polished and
deburred. If the ski is still hooky you might try a 1.5° base bevel in the
forward 15-25cm to soften immediate edge contact in the extremity.

4 - Many erratic behaving skis are actually the result of improper boot
alignment or canting.

Atomic's World Cup results are not a result of skis that are concave in the
tips other than the slight tunnel as described. Race skis are meticulously
tuned to perfection by ski team techs and don't resemble what is on dealer
shelves. Speed skis are usually a little convex because bases glide faster than
edges and you don't need or desire immediate edge hook-up at high speeds. End Quote.

Others here like VK and Yuki have expressed similar views on concave bases. For as long as I can remember the goal with ski bases was to insure that they were flat tip to tail. This was especially true for hard snow conditions. Then wider skis came along and concavity especially at the tips and tails became a greater issue with many skis (Atomic and others) arriving from the factories.

Based on my own experience, and the totality of what I have heard and read I have a hard time believing that concavity is either a design feature or desirable for all new generation skis in typical packed powder or harder conditions. I can see that for some skis and conditions it may not make a discernable difference.

post #22 of 24
We had a similiar discussion in the spring! Check out
post #23 of 24
I'm not arguing with anyone here, just saying that I've never been on a more versatile, high-performance ski and it just so happens to be slightly concave (and I've tried a lot of skis). Maybe it's a great ski in spite of it, maybe becasue of it. I don't know and I don't care. [img]smile.gif[/img]

I copied Betaracers old thread into here becasue it was the explanation the original poster seemed to be asking for.
post #24 of 24
Thread Starter 
Once again thanx for all the extremely informative posts. I am always thrilled to recieve helpful replies.
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