In the third part of the ski building series, we finally get to the ski building itself. The actual construction phase, the laminating itself, is short and relatively uncomplicated. It is more important that all the parts fit together, as there is no time to make improvements during the laminating process.
The ski core
A good wood core is crucial for a good ski. In order for such a wood core to do its job in a ski, it needs to be shaped. In the case of ski construction, it is sufficient to first give the core a height profile. If you look at a ski from the side, you immediately notice that skis are thinner at the front and back than in the middle. This is how the core should look when viewed from the side. A thickness of 2 to 3.5 mm at the ends and 9 to 12 mm in the middle has proven successful.
The thickest part of the core should be the central point of the ski, i.e. the so-called boot center. If you want to optimize this a little: the optimum central point depends on the skier, does he or she ski more on the forefoot or with the heel? The point can be adjusted depending on this. However, such considerations belong in the planning and preparation part of ski construction... It has been proven that for more traditional skis with a normal shovel, around 57% of the effective edge length should be in front of the center point. Powder snow skis can be longer at the front (up to 60%), park skis shorter (a pure twintip that is really skied switch 50%).
Longer shovels, tails or rocker constructions change these rules of thumb. A well-designed ski will have very similar percentages for both the "length over all" and the effective edge length in relation to the center point. Curiously enough, skis that deviate from these construction rules ski very "strangely". For the core thickness, you can also build a flat platform for the foot/binding and then cores that slope down towards the ends, or directly sloping down from the center point, or all kinds of intermediate shapes with plateaus, more or less strongly decreasing wood thicknesses, etc. The thicker a wood core is at one point, the harder it is at that point. Abrupt changes in mm thickness result in a less linear (i.e. less harmonious) flex. This can be desirable, for example if you want to build a shock absorber into your ski for rock jumps, but it can also boomerang and make a ski unrideable.
True ski builders use different types of wood for the cores at specific points and process the cores in such a way that the exact characteristics of a ski are created that are desired and required. Experience is key here, but you can't go wrong with the usual linear decrease in mm thickness from the center point to the ends. Rule of thumb: lighter and weaker skiers need thin ski cores, heavier and aggressive skiers need thicker ones. Example for a 60 kg skier who skis rather comfortably but likes to ski in powder snow: 2.5 - 9.5 - 2.5 mm. The cores can be profiled using a variety of techniques. Completely by hand and with a hand plane. This is very time-consuming, but precise. It can be done quickly with a hand plane and a sanding machine, but less precisely. Or you can build a special mold. There are plenty of suggestions for such molds on www.skibuilders.com, but they are usually not worth the effort. If you don't have two left hands and are patient, you can get very far with a sliding gauge and a plane. The luxury version here is called: CNC machine.
The ski shape
So, (whoever says "so" is far from finished). So now the ski is planned and on paper, the two ski cores already have a height profile. The shape of the ski is still missing.
For this, it has been printed out on a scale of 1:1. These prints are attached to the ski base and cut out accordingly. The thicker and stiffer the prints are, the better this works (it is also possible to glue the template onto wood). You can get reasonable results with a good pair of scissors, but cutters or sharp knives also work. Ski base is funny stuff: because when you cut it, it warps a little afterwards. To keep this warping to a minimum, it is a good idea to cut out the base roughly at first, leave it to rest and only cut it out precisely after a few hours.
When planning the template, it is very important to include the ski edges. These make the base wider. So of course you cut out the base exactly as much smaller as the edges then widen the base again to maintain the desired dimensions. Right-angled pockets at the ends are a good idea, otherwise the edge will later protrude beyond the facing at the ends. After the edges have been cut to the correct length (a little too short rather than too long), they are fixed to the covering with superglue. This fixation does not hold the edge to the ski but is only intended to keep the edge in position. Therefore: use little superglue. The edge is only finally fixed to the ski during pressing. The edge must, of course, fit as precisely as possible. Now the mold is ready, it is covered with a thin plastic sheet so that the ski can come out after gluing, the ski cores are ready and the edges are fixed to the ski base. And everything else that needs to go into the ski, e.g. the glass fibers, has been cut to size.
Pressing!
You should also now be aware of how you want to press your skis. The vacuum method is described here, as it is much more affordable for private ski makers. You will need a vacuum pump and a vacuum hose. Both are available on the Internet in the required dimensions. If necessary, an old refrigerator pump will also do, but thicker ones with plenty of "bang", i.e. power, are of course better.
Design
But wait! The skidesin is still missing. Curiously, the design seems to be the most important thing to ski manufacturers. There are various options. A thin wood veneer is very suitable as a topsheet. Such skis look very classy, but require a lot of care. It is also possible to use a purchased topsheet. This can be decorated with a motif at some print shops. However, it MUST be a sublimation print, otherwise the topsheet will not adhere to the ski (provided the side to be glued is printed to protect the graphic). Or you can place a sheet of thin, printed and washed cotton fabric under the topsheet. Just as you like. Of course, you can also use any design fabric to achieve a carbon fiber look, for example.
Resin
Ok, so now everything is ready. Really everything? Not quite... As long as the epoxy resin and hardener are ready to mix, you can almost really get started. First of all, the ski base has to be fixed in the mold as the bottom part of the future ski. How you do this is up to you, e.g. with adhesive tape or small nails. You also need to make sure that you mark and fix the ski cores so that they really do find the right position quickly during construction.
The hot phase: time is running out!
So: Preparations complete! Now the really hot phase begins. Hot phase, because from now on nothing can be changed in a makeshift manner, and also because epoxy resin with hardener can start to boil dangerously in large quantities. So only ever mix small quantities! The pot life of epoxy resins must be taken into account. This indicates how long the resin can be processed, i.e. how long it remains liquid. Resins + hardener with a pot life of around 40-60 minutes are suitable for ski construction, although there are differences depending on the manufacturer. Incidentally, the mixing ratio specified by the manufacturer must be adhered to as precisely as possible in order to achieve optimum results. The best way to do this is with a digital kitchen scale. Important: Only ever use the finished mixture of resin and hardener. As little resin as possible should be used, but of course enough should be used. Resin makes a ski heavy and is very brittle without fiberglass. Unfortunately, using a lot of resin does not help much here. Fiberglass manufacturers always indicate the optimum amount of resin to be used. Add a little more and you should be fine. Mold with inlaid coating is ready, all material is prepared and ready to hand, everything is clean, vacuum pump + vacuum hose + sealing material are ready?
Starting shot
Yes, now the starting shot, the time is running:
1. coat the base with the resin and hardener mixture, paying close attention to the T-pieces of the edges.
2. lay on the first layer of glass fiber and coat with epoxy resin mixture until the layer is saturated.
3. now fit the ski core correctly aligned and well coated with resin and hardener at the previously applied markings and fixings.
4. lay on the second fiberglass layer and coat sufficiently with resin mixture.
5. Design layer, soak with mixture if necessary.
6. Place topsheet the correct way round (some have a protective film on top).
7. Place tear-off film + absorbent fleece + mesh fabric.
7. Pack mold + laminate fabric into the vacuum hose.
8. Close the vacuum bag airtight and connect it to the pump using a hose.
9. Switch on the pump, which will suck out the air in the bag.
10. Depending on the strength of the pump, the air will now escape from the bag; you must now take care that nothing can be sucked between the layers of the laminate structure. It is best to simply press the ski into the mold with your entire body weight.
11. As soon as the vacuum has tightened, it pulls the ski into its future shape.
Now it's time to wait. The vacuum must now be held for several hours, between 12 and 24 hours depending on the manufacturer of the resin/hardener mixture, so the pump must always be running. The warmer it is, the faster it goes, below 20°C usually little happens. However, you should not heat above 70°C either, some resins cannot tolerate high temperatures.
Almost like Christmas!
Then the moment has come, the ski has hardened in the mold, the vacuum pump is switched off and it really is almost like Christmas. The ski is about to see the light of day. The vacuum bag is cut open, the perforated film + absorbent fleece + mesh fabric are torn off, tataaaaaaaa. It still looks quite funny ... so angular ... and somehow "rough". That's right, because it is. Before it goes into the snow, it still has to be worked on. Jigsaw at hand and cut along the edge as precisely as possible. Then go over it with a belt sander (or use the good old manual method) and expose the edges, shape the contours of the shovel and tail and the ski is practically finished. If there was a protective film on the topsheet, you can now remove it. The base should be sanded and of course waxed and the edges sharpened. The new ski can be ridden without any problems after about two to three days, although the epoxy resin will still set a little, but about a week after demolding is the time when the beautiful vehicle should be tried out at the latest. Skibuilders (especially the forum is great!) www.skibuilders.com Boardbuildingsupply (material) www.boardbuildingsupply.eu Skibaumarkt (material) www.skibaumarkt.de Skidesignanbieter www.freaksoffashion.com Ski building site for basic configuration www.skibau.de SnowCADX & numerous tips www.grafsnowboards.com Ski building seminars (the author is one of the ski building trainers) www.skibuilding.com
