Sanding your bases

[wanghoeby]

I've got a pair of skis with a super rough base almost like sand paper. Anyway, one of the local area shops said they can't grind em cause they don't have enough p-tex left. Can I just hand sand them with some super fine sandpaper? Would this work, or would I destroy the bases? Any other ideas?

[yesIsaidyes]

I've only heard of sanding the kick zone in classical XC skis or sanding an area where you dripped p-tex. It may work but maybe you should try a ptex peeler or metal scraper (perhaps it would remove less p-tex than a base grinder?) first...or find another shop?

[marshalolson]

get a razor blade and drag it along the base lightly instead of sanding.

go tip to tail only.

don't cut into the ski like this:

/-----------\--------
\--------------------

rather drag it along the ski so you don;t take out a chunck like this:

/-----------/---------
\---------------------

(if that makes any sense...)

apply generous wax


EDIT: NO MATTER WHAT YOU DO, DON"T SAND IN A ROTARY MOTION - ONLY PULL TIP -> TAIL

[summit]

Find a shop with a belt grinder instead of a stone grinder. (jetlag brainfart)

[Spats]

JONG question: what's the difference between a belt grind and a stone grind?

[cold_smoke]

You can manually sand them if a shop will not belt them. Get a very, very fine grit sand paper (I want to say 240, swix actually makes some if you want to buy the same stuff for 5X the price). Wrap the sandpaper around the file and do a few non-stop passes tip->tail.

[Conundrum]

JONG question: what's the difference between a belt grind and a stone grind?

A belt grind is actually wet sanding. Think of a giant belt sander with the belt passing through water that you can flatten and smooth a base with. A stonegrinder has a big stone wheel (feels similar to pumice stone) that water is sprayed on. With a belt grind you can only vary the grit of the belt. With a stone you can actually set structure patterns in the stone with a diamond blade contraption that passes over the stone at different setting controlled by the tuner. These stucture patterns are then transferred to the base as it's ground.

[splat]

JONG question: what's the difference between a belt grind and a stone grind?

A belt grind is done on a wide belt sander. Done properly, the belt will start with one grit and will be changed out to finer grits as you go. You have more grittiness than a stone because a proper stonegrind will have the stone getting leveled and/or structured prior to the grind with a pinpoint piece of metal. In terms of the grittiness, think of a stone as the finest of grits a belt just won't achieve. It's an actual stone-like substance, but can't you tell exactly what it is made of. That pinpoint etches the stone to make structures in the stone that are then replicated on the base.

here's some tech info about stonegrinds I found:

by John Underwood and Erica Alexander

Just when you thought it was safe to acknowledge your basic level of expertise as a competent ski tuner, stone grinding unveils a new direction in the unending battle for speed. Stone grinding matches micro-grooves in the ski base with the conditions or configuration of snowflakes. Cold, dry, transitional, normal and moist snow conditions can be prepared for with fine, medium or coarse structures. The temperature ranges that are associated with these conditions and grinds are: -60C to polar conditions for dry, +20C to -20C for transitional, and +30C and warmer for moist or wet.

In technical terms, micro grooves in your base provide channels which direct the points on a snowflake along the base of your ski from the initial contact point at the tip, to the compaction point underfoot, to the release point at the tail of your ski. The non-uniform nature of the stone grinding structure creates chatter as these snowflake projectiles jump from channel to channel as they move along the base. Stone grinding or conditioned structuring matches a random non-uniform grooving of the Ptex base with the projectile configuration of snow, resulting in minimal friction/surface tension between two planes.

A second advantage of structuring is that the micro grooves provide a reservoir for wax below the height of the structure. Imagine melting wax onto a glass countertop and spreading it out into a thin layer. The wax is not in the countertop; rather, it is sitting as a smooth, uniform coating on top of it. The same thing can be done to a perfectly flat ski base with no structure. The wax pools in a smooth uniform coating on top of the P-tex, but doesn't break the surface tension. In fact, it creates more. Therefore, as projectile points on a snowflake drag along the base from tip to tail, there is no chatter created by structure to keep them moving along the ski. It is critically important after stone grinding not to overfill the structure with wax thus creating a flat surface again. This can be accomplished by carefully brushing out some of the pooled wax so that you can see structure.