Introduction: Wooden Skis
After my wooden bike, I kept exploring all the possibilities of wood and as we are acquiring new wood working machines here in Fablab Moscow, the spectrum of possibilities widens. The winter is coming and I know that at some point, commuting by bike will become difficult. The obvious solution is to swap my bike for skis. Why not making my own skis? After all, one of my friends told me that it should be easier to make than a bike.
These skis are made for off-trail crosscountry skiing so they are wide (12 cm). As a first prototype I made them short (100 cm) to save material and ease the construction. Actually such skis are more suitable for children but now that I control the process I will make longer models.
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Step 1: Tools and Material
- Steam cleaner
- Hot air gun (optional)
- CNC router (optional)
- Jig saw
- Sand paper 180
- Plywood 18 mm (90 x 100 cm)
- Plywood 3 mm (48 x 30 cm)
- 6 sheets of wood 2.5 mm (13 x 100 cm) (Ash)
- Polystyrene foam 5 mm (13 x 100 cm)
- Wood glue
- Epoxy resin(120 g)
- 4 M8 x 15 bolts and 4 nuts
- Paper tape 3 cm wide
Step 2: Design
You need to design your skis. If you are not inspired you can copy an existing ski. There are four important parameters: Length, width, thickness and cambre. For an off-trail ski you need a large surface (Length x Width). I chose the width of my snow boots. Short skis are more manœuvrable. Long skis are more stable in high speed.
The thickness and camber are interdependent. Indeed the thickness is related to stiffness and stiffness to load distribution. The camber also modify the load distribution. So you can have a stiff and low camber ski who has the same load distribution as a flexible but very cambered ski. These two parameters are crucial for cross country skiing and specially for classic because the central part under the food has to grip during the impulse but is not supposed to touch the ground during the sliding part of the move. These two parameters are also related to the rider's weight.
I chose a length of 100 a width of 12 and a constant thickness of 0.75 centimeters. Commercial skis have their thickness varying along the length but it makes the construction more complex. As I used a CNC machine to make the mold I had to make a 3d model. You can simplify the process and draw directly on the plywood then cut it as desired with a saw.
Step 3: Make the Mold
The mold consist in 7 layers of 18 mm plywood. There is a hole at each end for alining and holding the stack together with bolts and nuts. It has been glued and bolted together and finally the inside surfaces were sanded. I finally added a layer of polyethylene foam 5mm on one inner side. It allows to smooth the irregularities.
Step 4: Bend the Tips
I had to bend the wood sheets to let them entering the mold without cracking. You need to bend the six wood sheets. Here is how I made:
- Let the wood sheet end in water for 10 minutes and start the steam cleaner.
- Spray the steam on both sheet sides during 20 seconds.
- Place the hot wet wood sheet between the two mold parts and add a clamp.
- With one hand start tightening the clamp and with the other hand heat the sheet with the hot air gun.
- Tighten the clamp completely and let it two hours cooling down.
Step 5: Ski Forming
Then glue each sheet layer (3 layers for each ski), place the stack in the mold and clamp it. Let it dry one night.
I used the wooden glue for this purpose but using epoxy would be more durable.
Step 6: Cut the Shape
The ski tips tails and sides are now cut with the jigsaw.
Step 7: Bindings
I opted for the simplest solution: a strap. Under the foot are glued two rectangular pieces of plywood 3mm. One with a slot for the strap and a second layer on the top.
Step 8: Epoxy Coating
I made some research in order to know what would be a good ski base. Traditional ski base are made of polyethylene. The surface has to be hydrophobic and slightly rough for an optimal slide. To simplify the construction I opted for a layer of sanded epoxy (0.5 mm, 60 g). It allows me to test different waxes or even adding a layer of polyethylene or skins.
To apply this base layer, I taped the sides with paper tape (cf. 1st image). I then spilled the liquid epoxy all along the skis.
Then deburr with a file (4th image) and then sand with the 180 sanding paper.
Tape the bottom and add the top layer (40g) and sides with a brush.
Step 9: Conclusion
I am still waiting for snow but I think that the overall process is here.
I will make other models because I want a pair of fat free ride, a light pair for ski touring, another with tips on both ends for freestyle, another narrower for crosscountry in the trails and, what else? I forgot.