Grinding; Bases Not Rails

[Bad Wolf]

Until recently I had heard of posters grinding the bases of their boards, but I just guesses it was something "tinkerers" did. I did a little research on the subject today and now feel like I've been missing out on something.

There seem to be two kinds of base grinding. The type done with a sanding belt seems to be used for smoothing out and flattening damaged or repaired bases, or just giving them a new finish. Then there is stone grinding, designed to put a pattern on your bases to help them slide better. Apparently there is a whole science to this, involving differing patterns for varying conditions and requirements. It seems like racers really get into stone grinding.

Then there are folks who grind their bases to tune the board and even change the ride characteristics.

Some people, like me, have never ground their boards, whilst others grind them every week. What do you guys do and is grinding something worth finding out about and getting into?

[Bluewing]

I am not an expert in this but did some research recently before I got a full tune for my 120s because I needed a big gouge repaired and a full tune wasn't much more than the gouge fix. There is a lot of information out there some of it very detailed and technical especially if from a racing perspective. I found this article about ski tuning in general that also contained information on base grinding (wet belt to remove imperfections and produce a flat base) and stone grinding (to add structure to the base). From what I could tell this is the process that the tune shop at my local mountain uses - they tuned my 120s. The idea from what I learned is to grind the bases to get them flat and smooth and then do a stone grind to add structure which puts a pattern of small striations into the bases to help the board track properly and run faster over the snow. The structure helps to move the water that forms under a ski when running in the proper way.

http://skiing.about.com/od/skis/ss/preseasontuneup.htm

I was very happy with the improvement in my 120s performance after the tune. Part of it was having the edges done up properly again and part of it was from the base grind and structure (the boards had much more structure after the tune than stock out of the box) since the boards had significantly more glide and were definitely faster.

One interesting note is that the performance of the boards should continue to improve for a bit while the wax builds up on them again after several waxing. I guess the wax has to resaturate the base material, which takes several cycles of application.

Since this removes base material I don't think it is something you want to do any more often than necessary. People who race and expect their equipment to be expendable to gain maximum performance might do it often.

[slow]

Keep in mind that when many of us refer to a base grind, we are referring to having both the ptex flat and the base edges at zero degrees (flat to the ground). It is the base edges at zero degrees that we are looking for, more so than flat ptex.

IMO there are a number of factors to consider prior to grinding your bases to achieve a zero base edge:

1. If you are going to be in the terrain park and riding rails and boxes or doing jumps, you do NOT want sharp edges that can catch either on the terrain elements or when you land. Therefore no value in getting a base grind.

2. If you like to spin, a 1 degree of base edge angle makes spins easier since you are less likely to catch an edge and it requires less attention.

3. If you are one of the fortunate few that get to ride soft snow and you rarely ride hard pack and ice, there is no value in base grinding or (even tuning side edges). In soft snow the base and edges have no effect.

4. In hard pack and icy conditions, if you are an aggressive rider that gets the skiboards up high on edge, there is less benefit to having a flat base and base edge than if you are a rider that runs the skiboards flatter and expects an immediate and predictable response with subtle inputs to the skiboard. Therefore a rider who has a taller stance (verses gorilla) usually likes to have a base grind and well tuned edges so the skiboards respond predictably with minor inputs while cruising.

5. One other benefit of a properly done base grind is that it opens up the ptex to accept wax.

Since I ride mostly hard packed manmade snow that can be icy, I do not spin frequently and I am a cruiser, I like to keep my base edges at zero degrees with a 88 degree side edge.

In my experience, newly fabricated skiboards take about another 2 months for the bases to stabilize. I assume it is because the adhesive is still curing. While curing it "sucks in" the ptex. Therefore when a newly fabricated skiboard is received, it may appear convex on the ptex. Base grinding at this time can result in a concave base (ptex) after it sets up and you may require a second base grind.

If you have a new skiboard and want predictable edges my recommendation is to use a steel ruler on edge to confirm that the base edges are "close" to being flat. If the outside of the base edge is no more than a couple of paper thicknesses away from the steel ruler, ride them for a few months without a base grind.

Remember that when you base grind you are removing ptex and steel edge, thereby potentially shortening the service life of your skiboards. So only base grind if needed.

[Bad Wolf]

So when you talk about grounding them "flat" and a zero base angle, you are talking about getting rid of any camber on the boards ? (sideways/convex).

What purpose would that camber serve in the first place?

[slow]

So when you talk about grounding them "flat" and a zero base angle, you are talking about getting rid of any camber on the boards ? (sideways/convex).

What purpose would that camber serve in the first place?

The flat and zero base edge angle is across the width of the skiboard, not along the length. Therefore it is not effecting camber.

Camber is the arc in the bottom of the skiboard along the length when unloaded. It is a design feature to load the edge evenly along the edge's length and to give "pop" out of a turn. If there was no camber, the edge would be more heavily loaded under foot and decrease the further you go toward the tip or tail of the skiboard.

[Bad Wolf]

Thanks

[slow]

A few other tid bits of info. It is desireable to have the ptex and base edges flat. Any changes to performance characteristics is then made by adding some angle to the base and side edges, not the ptex.

If the ptex is convex across the width (bulging away from the top sheet), the skiboard may be unstable at high speed and there may not be much edge grip thereby requiring more lean to get the skiboard to edge. If the ptex is concave across the width (depressed toward the top sheet) the skiboards may feel hooky (catch edges), turn abruptly and not be smooth in transitions when linking carves. Flat ptex is neutral and does not contribute these issues.

Check out page 60 of Tognar's catalog (page 61 of the PDF) for a Quick Fix Chart: http://www.tognar.com/content/tognarcat1213.pdf

Note that it is desireable to tune skiboards with a zero degree base edge angle whereas skiis and snowboards are generally tuned with a base edge angle other than zero. That is why it is important to ask for zero degrees if having a shop tune your skiboards.