One of the few things consistent between all of the various shapes, sizes, side wall and top sheet shapes, binding locations, and camber/rocker, etc of skis and snowboards is that they are symmetrical relative to their longitudinal centerline.
Finding the centerline with accurate measuring and layout tools is critical when drilling for and mounting bindings or checking their proper mount locations from the shop. Not only for side to side symmetry, but to assure they are in line with the ski.There are many simple and complex tools and approaches employed using any number of measuring and layout tools to determine the centerline. Some are accurate and some are not.
The first two thing to remember is that in order for your skis to perform as designed is that bindings need to be centered relative to the edges and NOT the top sheet or side walls AND the sides of skis are typically not straight, but curved. Additionally, their proper fore and aft location is important and establishing an accurate centerline assists in this regard.
Cautions: Without factoring the curvature of the ski sides, simply using a try square or intersecting diagonals or intersecting arcs can result in minor to major inaccuracies.
Granted, the turning radii of many skis is large enough that measuring from both sides using a square can be reasonably accurate if not used absolutely and directly across the skis,
while using crossing diagonals and arcs can result in large discrepancies. Top sheet graphics and variable side wall shapes are other sources of inaccuracies. Whether a skis is cap or sandwich construction or symmetrical top sheet graphics, they are not to be relied on for measuring the skis other than general dimensions.This leaves the edges as the ‘benchmark’ for the lateral ski dimensions (as well as for base flatness). Accurate measuring tools like calipers, tape measures and rulers can easily find the width from edge to edge, but are not necessarily the easiest or accurate or reliable tools at transferring measurements to the top sheet for marking.
Easy & Accurate Techniques: A very useful aid is to place a strip of masking tape down the perceived center of the ski. If you don’t have tape a grease pencil on the top sheet works as does a clamped piece of string or straight edge. The longer the straight edge or distance from your end marks, the more aligned your centerline will be. If the marks are closer and you are slightly off center with one of your marks, the angle of the centerline will be greater than if they same two marks are farther apart.
A center rule, ideally with edge guides or ‘locators’ is the simplest and quickest reliably accurate method to mark a center line. The math is eliminated and you simply need to match the measurements on each side of center to set the center.
This PDF centering template can be used to by folding it over the ski and creasing it over the edges at the same measurement and tape it. You can mark each end and then move the template other locations and use it on the other ski.
Using the common try or double square, is another easy option for finding center. Rather than spending time micro-tuning the blade location (with the handle against each edge) go ahead and ballpark the length either
just long or just short of center and make a mark along the end of the blade. After you have two marks, measure in between them to find true center.
Always double check your measurements, before, during and after drawing your centerline.
Once you are confident your line is indeed the center of your skis, you can square against it at the ski’s mounting point to draw your center line for your boot center and tape on your binding template and are ready to mark and drill for an accurate binding mount.