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ski base question

post #1 of 12
Thread Starter 
Checking my bases with a stright edge I notice some concaveness just behind the shovel and just in front of the tails, both in the widest part of the skis, and very little at the boot. I did this with hte straight edge and a light.

MOD X, used one season mostly on wet,heavy, spring snow.

How much light or millimeters are allowed before I should regrind?
post #2 of 12
JYD, unfortunately a lot of skis come this way from the factory. If it's not a lot I would just flatten the areas with a file.
post #3 of 12
You can't flatten a concave base with a metal file; you can flatten only a railed ski w/ a metal file.
(Otherwise, all you're going to do is increase the base edge bevel.)
If you really want to flatten a concave base, you need a stonegrinding . . . or you can try your luck w/ the Ski Visions tool. (Can work, but requires skill, effort, and time.)
post #4 of 12
Thread Starter 
Thanx for the help. I'll do it at our shop. I just didn't know how much was too much. I'll probably mess up the structure. All we have is an SNB80 belt Wintersteiger. it might keep some structure. The manual says to do tip first then tail, then tip again. This is suppossed to help. But then, it's a straight and rather wide structure which is usually for warmer snow.
I can see myself glued to the side of a mountain on a double black, wtationary! Other than from the factory, I wonder if concaveness comes from incorrect ski technique?
post #5 of 12

You are teasing me right?

It would take an awful lot of miles on the snow to wear away the base to become concave. (Sand Skiing maybe less miles)

There are some race guys who like a bit or RAIL in the base fix.

With the shaped ski you might get away with it a little more than with the older type side cuts.

The guys who used to RAIL their skies are real crankers who are on HARD PACK, like ICE. The rail effect is negated by being UP on the edge and not useing much p-tex at all for the dynamics of the turn.

As you discribed the soft snow you are on I can not help but think that correcting the base may assist you in truning the skis a bit more! (or at least easier)

Careful with the stone grind though that is usualy what starts it in the first place. Some guy in the shop rushes the grind and you guessed it, Base material goes faster than metal, hence the shallow middle!

post #6 of 12
For a finer structure w/o using a stone try a fine grit CARBIDE sand paper. This will give your skis a decent structure. if you use usual sand paper the grit will come off and get stuck into the base.
post #7 of 12
I agree that many skis, unfortunately, come from the factory with concave bases, especially skis with very wide tips and tails. For practical purposes, for most skiers, if they are flat for an inch or so in from the edges and not TERRIBLY concave otherwise, they'll probably ski all right.

There was a discussion here last winter where it was revealed that some Atomic skis come concave from the factory intentionally. Apparently it was a compensation for the skis' torsional flexibility or something. I can't confirm it, only that someone brought it up here, but it's an interesting thought!

Best regards,
Bob Barnes
post #8 of 12
Jyard My Mod X ski's are exactly the same and they were that way when i got them brand new. Mine ski fine, maybe am on edge alot cranking out turns but iam leaving mine alone. On mine with a straigh edge you can barly see under in fact without a flash light i couldnt even tell. With a flash light i can see just a little light from under the straight edge.

<FONT COLOR="#800080" SIZE="1">[ November 08, 2001 08:56 AM: Message edited 1 time, by dc9mm ]</font>
post #9 of 12
Thread Starter 
I really appreciate the input here. I got my MOD X's mid or late season last year. So there hasn't been much use yet. They seem to ski just fine. In the places I mentioned I see the light dead center for about an inch or two, but flat by the edges. But I think I goofed here. I still have the old wax on. Perhaps I should get all that off first and check again with a sweaky-clean base? Tip and tail are exactly the same- dead center.

But then, maybe I'm just being a worry wart. ANy of you might check my skis and say, "JYD, what you been smokin', Boy? Ain't nothing wrong here! Quit worrying and go take a few runs!"

If I do have to regrind, all I have is an SNB80 belt grinder-Wintersteiger. We have 80, 100, and 120 belts. If I do regrind, should I just go with the 120 and take my time with a few passes?
post #10 of 12
Jonathan S, What's the difference between concave and railed? I have had bases that were lower (not a lot) than the edges in the tip and tail area and was able to get them flat with a file unless my true bar is lying to me. These skis were lower in the center of the base than near the edges. I thought that was concave.
post #11 of 12
Thread Starter 
Lucky- What you had was concave. Railed, as I know it, is when the edges stand out further than the bases, regardless of the base being concave or convex. Picture a set of RR tracks. The tracks are the edges, in between the tracks is the base. Wouldn't that be great for straight runs, but rather exciting for turns?
post #12 of 12
A concave base has ptex that is not perfectly flat across its entire width; if placed on a flat surface, the middle of the base's width would not be touching the surface.
A railed base is essentially when the ptex is perfectly flat, but not in the same plane as the edges; if placed on a flat surface, the edges would touch the surface, but none of the ptex would touch the surface.

A convex base also has ptex that is not perfectly flat across its entire width; if place on a flat surface the middle of the base's width would touch and the ski wobble back and forth.
A recessed-edge base also has ptex that is perfectly flat, but not in the same plane as the edges; if placed on a flat surface, the edges would not touch the surface, but the ptex would.

A concave base is fixed via stonegrinding, although if the concavity is severe, you'd lose a lot of the ski's life in an attempt to make it flat. (And if you tried flat filing it, since a file takes down only metal, and a negligible amount of ptex, you'd just over-bevel the base edges.)

A railed base is easily fixed via flat filing. (Railed bases were very common in the days of beltsanding.)

A convex base is also fixed via stonegrinding, but you have to very careful not to essentially cant the ski when making it flat.

A recessed-edge base is exactly what you want, though very difficult to achieve, so a 0.5-degree base edge bevel is the typical substitute.
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