A pair of old skis are still useful if they still have a flat running surface, a sharpish edge and are rigid enough to form the base for a multi-person toboggan. Here's how one builds such a toboggan.
The objective of this toboggan design is to:
Be as light as possible
Be as strong as possible
Be as fast as possible
Send 2 adults or 12 very small screaming children down a hellishly steep hill
A pair of knackered adult's skis
A 8'x4' sheet of 9mm birch plywood
Strong contact glue
The usual workshop bits and bobs and consumables
Circular saw and cutting guide, or table saw
Router with spiral cutter
Clamps (you can never have too many!)
Step 1: Strip an Old Pair of Straight-edged Skis
Pre spoon shaped-era skis that still have a reasonably smooth surface are best. The longer the skis, the more people you can put on the toboggan. Here we have my wife's cherished and lovingly looked-after K2 skis. Yes, they will do just fine!
Remove the bindings with a large star-point screwdriver and throw them away.
Use a belt sander to roughen the top resin layer to create a glue surface. I went deep enough to remove the faded branding under the resin. This exposes a light plastic material that may in your case be slightly porous, so it you sand this deep, be sure to thoroughly cover the exposed surfaces with polyurethane varnish in the last step.
Step 2: Cut the Plywood Frame
Decide on how long you want the toboggan to be, depending on the length of the skis. For a pair of 165cm ladies skis, the length of the top deck was 110cm, which can comfortably seat 2 adults.
The entire design is based on 15-degree angles, so set your circular saw and angle-gauge to this angle. The sides are 20cm high and the deck is 30cm wide.
Also cut 6 long stringers about 3cm wide from which the bottom ski-mounting rail and the top rabbet-rail will be formed. See the rough cutting plan and the angles at which you need to cut your boards.
I used a cutting guide for a perfect, straight cut with my circular saw. (And my saw also has a laaayzer, dude!)
Step 3: Cut Out Fillets on Side Panels - Part 1
Reduce the overall weight of the toboggan by some 35% by cutting out fillets in the plywood. The general approach is to create a cross-brace design like you see on old iron bridges. Keep the strutts at least 3cm wide.
Because this is a repeating pattern, I created a cutting jig from a scrap piece of high-density fibre board (the type they use for cheap wood-effect flooring) and cut my pattern with a jig saw and smoothed it with a drum sander (sandpaper on stick will also do). Remember to leave enough surround on the jig to clamp it to your workpiece such that the clamps do not interfere with the router when you use the jig to cut your fillets.
I used a combination of double-sided sticky tape, self-tapping screws and clamps to hold the jig to the workpiece and completed the one side with a cutting bit on a 1/4" hand-held router.
Use a drum sander (or sandpaper on a stick) to round out the corners, because this side now becomes the cutting jig for the other side.
Step 4: Cut Out Fillets on Side Panels - Part 2
Clamp and Double-side-sticky-tape the two left and right hand-sides together (the one has fillets cut out, the other still blank) and run the router with its cutter over the entire assembly. Smooth the corners out with a drum sander.
Step 5: Cut Out Fillets on Deck Panel - Part 3
I re-used the original cutting jig to cut out fillets from the deck panel and a large forstner drill bit to make decorative holes. It occurred to me ofterwards that because people will sit straddled on this panel, that the pattern should have been symetrical. Oh well, some folks don't have symetrical butts in any case...
Step 6: Cut Out Fillets on Panels - Part 4
Round the edges of all the fillet holes with a 4mm round-over bit on a router, on both side of each panel. This will create a comfortable grip for holding on to. Make sure that the bit depth is less than half of the thickness of the material, or the round-over cut on the opposite side will ride on the previously-made cutting surface, which result in an user-unfriendly sharp edge.
Save the fillet cut-outs for something useful.
Step 7: Glue Stringers to the Side Panels
Use PVA wood glue or similar to glue to two stringers to the bottom of each side panel so that you have a tripple-width plywood bonding surface to the skis. This enlarged bonding surface is important since the plywood frame is actually contact-glued to the skis - more on this later. Glue a stringer to the top of each side panel so that it creates a rebate for the top panel to sit in. Remember in both cases to observe the 15-degree angle.
Clamp it up and let the glue cook.
Step 8: Assemble Left, Right and Deck Panels
Assemble left, right and deck panels, observing the 15-degree angle. Use standard PVA wood glue to the deck panel into the rebates created by the stringers that were attached to the top of the side panels.
Use the sketch below to work out which surface needs to be glued to which surface.
Step 9: Create Front and Rear Gussets
Use two pieces of left-over plywood and trace the shape of the gussets out. If you are not versed in 3-dimensional geometry, then you might be surprised to see that the side angles are not 15 degrees any more. I hope that you have been paying attention at school. Cut out a curve at the bottom of each gusset to allow snow to pass underneath the toboggan. The shape of this curve is not particularly important, but don't loose too much strength due to a too deep curve, since from a structural point of view, these gussets are very important.
Glue the gussets to the front and rear. When the glue has set, trim the excess from the stringers and run a rounding-over router bit over all the upward-facing and forward- and backward-facing edges, and the inner curves of the gussets. Leave the bottom edges flush, though.
Step 10: Align to Ski's Profile
Skis vary in thickness along their lengh, so the bottom toboggan rail needs to be shaped according this profile for a perfectly flush fit.
Clamp the ski flush to flat work surface and place the toboggan rail next to it, resting on top of spacers of the same height as the lowest height of the ski's profile. Decide how far back you want the frame to be on the skis. Trace the ski's profile on to the toboggan rail. Keep in mind that the profile shape is not symetrical along the length of the ski, so repeat this step on both sides with the ski pointing in the same direction.
Use a hand plane or an electric plane to remove the excess material from the toboggan frame.
Step 11: Attach the Skis to the Toboggan Rails
Mask the areas off that do not need to be glued with masking tape.
Spread contact glue on both the skis and the the toboggan rails. Wait 10 minutes (or whatever the glue manufacturer says) until the glue is touch-dry. Carefully contact the surfaces and then clamp for a few hours.
I found that the contact glue made the surface of the skis a little mushy because I removed the top resin layer and exposed the slightly porous type of plastic material. I still got a strong (but messy) bond in the end, but I would try two-part epoxy glue next time.
Step 12: Attach Reins
This gives you something to hold on to, and also provides a limited amount of steering by pulling and so bending one or the other ski.
A long piece of packaging webbing is ideal here. You can get this from boxes that large computers / servers / printers get shipped in.
Attach the webbing - folded over once - with countersunk screws and large washers to each ski. Recess the holes in the running surface on the skis so that the countersinks do not stick out. Heat up a screwdriver with a blowtorch and use this to make holes in the webbing, aligned with the screw holes. This will prevent any fraying. For the same reason, seal the webbing's cut ends off with a blowtorch.
Step 13: Paint With Polyurethane and GO PLAY!
Well, what can I say? Paint the frame and the top of the skis (if you removed the resin layer) with a few coats of Polyurethane and go play!
This toboggan put all the other toboggans and sledges on our village hill to shame today (18JAN2013), being the fastest one and the one that went the furtherest. It travels in a dead straight line and a limited amount of steering is possible by pulling on the reins. The overall weight is about 12kg. After many runs and spills, the structure has held out very well - no cracks, no creaks, no splinters.