Introduction: The Ski Sled
Runner Up in the
Woodworking Contest 2017
If you were raised sufficiently far north I'm sure you can relate to the joy of waking up to snow covering the ground. My favorite thing about the white stuff is the way it decreases the coefficient of friction between the ground and an object sliding over it. In other words, I love sledding! More than likely this love was inherited from my dad, who one year took an old runner sled and fastened some old skis along the bottoms of the runners. When everyone would get together, this "ski sled" was the fastest sled down the hill, but the addition of the skis kept the runners from flexing - meaning it only went in a very straight line.
Several years later, my dad and I tore apart the ski sled and rebuilt it. This second ski sled had a rudimentary steering system, which worked by flexing the fronts of the skis. Although this system allowed for some steering, it was far from perfect. Then two years ago, I took this sled down an extremely bumpy no winter maintenance road. By the bottom of the mile-long hill, virtually every board on the sled was shattered.
Although, this second ski sled was dead, I knew that one day I would build its successor.
Step 1: Design
Immediately after destroying the second ski sled, I began designing the new sled. I had four main design objectives for this new sled. First, its frame would be made from aluminum to ensure that it would be durable, while keeping its weight as low as possible. Secondly, it should turn better than the previous sled. Third, it would have to be relatively easy to build (In other words, I didn't want to have to weld aluminum tubes together). Finally, riding a sled 1 mile down a bumpy road had me intrigued by the idea of adding suspension. Not only would the suspension make the ride more comfortable, but could also improve control through the rough bits.
I designed the sled in Sketchup around these 4 design criteria. For steering, the skis would pivot along their entire length. Tie rods connected between the handlebar and brackets attached to the skis would tip the skis left or right as the handlebar was turned. Although simply tipping the skis will not cause the sled to turn, it was assumed that with my body weight primarily on the rear of the skis, they would twist along their length, introducing a turning action.
For the suspension, it was decided that two control arms would be used to connect each ski to the central frame of the sled. This frame would consist of a central box tube running the length of the sled, with three smaller box tubes protruding from its sides. The suspension control arms would be attached to the front and rear protruding tubes at points close to the central tube. Small, bicycle shocks would be placed between the ends of the control arms and the ends of the protruding box tubes.
I decided to use wood for the decking and handlebar. There were two reasons for this. First, using wood made the construction of the deck relatively easy. Secondly, I wanted the finished sled to have a classic look (think an old-time Flexible Flyer sled).
I can't stress how important a full 3D model was to the success of this project. Not only did it eliminated all of the guesswork in knowing if the suspension and steering would freely move through their entire range of motion, but it provided an accurate guide for fabricating each part of the sled.
Step 2: Preparing the Center Box Tube
The core of the frame was constructed from a 3' long 1.25" x 2.5" aluminum box tube of 1/8" in thickness. Several holes were cut in this box for mounting of the handlebar and the perpendicular protruding box tubes.
After drilling a 1/2" hole for the handlebar pivot bolt, a notch for the handlebar to rest in was cut from the end of the box. I cut the sides of this notch using a hacksaw and then drilled closely-spaced holes along the bottom edge, which allowed me to easily break out the notches on both sides of the box tube. Once these aluminum pieces were broken away, the notch was smoothed and squared up using a file.
The trickiest holes were the three square holes which needed to be cut through both sides of the box. The perpendicular box tubes would be slid through these holes and bolted into place. I drilled two large (~3/8") holes in adjacent corners of each of the marked squares. By dropping a jigsaw into these holes, I was able to connect the holes and roughly cut out the squares. A file was critical to smoothing out these rough squares so that they would perfectly fit the 1" x 1" box tubes, which would be slid through them.
Step 3: The Perpendicular Box Tubes
The perpendicular box tubes protruding from the sides of the central box were made from 1" x 1" aluminum box. I recommend using a stronger alloy of aluminum (I used Al 6061, vs. the more commonly available Al 6063), as there is considerable stress where these boxes pass through the central box.
After cutting these tubes to length, 1/4" holes were drilled vertically through all three boxes for mounting the decking. 5/16" holes were also drilled in the sides of the front and rear box tubes for mounting the control arms and tops of the shocks.
To allow the shocks to attach to the ends of these box tubes, a small notch was cut from the bottom ends of each box.
After cutting these notches, the bottom edges of the sides of the boxes (adjacent to the notch) were beveled slightly by cutting away the corners with a cutoff disk.
Step 4: The Control Arms
The control arms were made from a 1" x 1.5" aluminum box tube. Since the top of each control arm needs to be open to allow it to attach to both the frame and shock without interference, 1/4" was cut off the top of each box to form a 3/4" x 1.5" U-channel. Ideally I would have purchased a 3/4" x 1.5" U-channel, but this was not available from my metal suppliers. I drilled the 5/16" holes for mounting the control arms to the frame and shocks before cutting the top off the box tube to ensure the aluminum did not bend during drilling.
With the top of the box removed, the next step was to cut deep notches in the ends of each control arm. These notches allow the control arm to mount to both sides of the perpendicular box tube at one end, while straddling the width of the shock at the other end. After cutting the sides of each notch with the hacksaw, the bottoms were cut using a cutoff disk.
Four identical control arms were prepared and are presented along with their associated mounting hardware in the image below.
Step 5: The Shoes
Four small shoes were prepared for mounting the frame to the skis. These shoes were made from some 2" x 2" aluminum box tube that my father-in-law had left over from a fencing project. After the shape of the shoes was cut from the box, 5/16" holes were carefully drilled through them from mounting to the lower ends of the shocks and control arms.
Smaller holes were also drilled in the bottoms of the shoes for mounting to the skis. Note that three screw holes were made in the rear shoes, while only two screw holes were put in the front ones. Since the skis are considerably thinner at the location where the rear shoes attach, the extra screw was added to ensure a secure connection.
Step 6: Assembling the Frame
With all of the frame components prepared, I was ready to assemble them. The frame was assembled according to the sketchup design presented below.
Once all of the aluminum bits were sanded to smooth out any surface imperfections, I slid the 1" x 1" box tubes through the square holes prepared for them in the sides of the central box tube.
When I prepared these 1" x 1" boxes I did not drill holes in them for mounting to the central box. I wanted to first align them in the central box and then use the holes in this box as guides for drilling these holes. By measuring side to side, and using a speed square, I was able to ensure the 1" x 1" boxes were perpendicular and centered relative to the central box. Once I had this position nailed down, I drilled the 1/4" mounting holes through the 1" x 1" boxes.
After bolting the perpendicular boxes to the central box, I proceeded to bolt the tops of the shocks to the frame. I used shoulder screws for these connections as well as all of the other suspension connections, which are required to pivot freely.
With the tops of all four shocks mounted, I mounted the control arms to the frame. Once again, shoulder screws were used. Washers were used to fill the gap between the sides of the control arms and the 1" x 1" boxes. I just kept adding washers until there was minimal side to side play.
With the control arms and shocks bolted to the frame, their bottom ends were jointed to the shoes for mounting to the skis. Once again, shoulder screws and washers were used for these connections. It should be noted that I applied a small layer of grease to the shaft of each shoulder screw to help lubricate each pivot point.
Step 7: Prepare the Wood
The handlebar for the sled was made from a piece of 1" thick cherry. After planing the cherry to the correct thickness, I cut out the shape of the handlebar using a jigsaw. The edges of the handlebar were smoothed using a 1/4" round-over router bit.
Two pieces of 1/16" thick aluminum were cut to fit the top and bottom of the handlebar. These aluminum plates add strength to the handlebar where it attaches to the sled and also provide a smooth surface for where the handlebar pivots inside of the central box tube.
Holes were drilled through these aluminum plates for both mounting to the handlebar (the 1/4" holes) as well as for the 1/2" pivot bolt.
A vise was used to hold the plates in place over the handlebar and these holes were continued through the wood.
With the holes drilled completely through the handlebar, the plates were bolted to it using two 1/4" screws. Next, two angled holes were drilled for the bolts, which would be used to support the tie rods used to tip the skis. Previously-drilled holes near the ends of the aluminum plates were used as guides for the location of these holes on both sides of the handlebar. I began by drilling the angled holes approximately half-way through the handlebar from the one side. Then, I flipped the handlebar and completed the holes from the other side. This method ensured that the completed holes were at the correct angle through the handlebar.
With all of the holes drilled, the completed handlebar was mounted to the frame using a 1 1/4" long shoulder screw. As with all of the other pivot points, the shaft of this screw was greased. I also applied some grease to the surfaces of the aluminum plates so that they would slide smoothly inside of the notch in the central box tube.
Step 8: The Deck
The decking was made from a single 1" thick board of cherry, which was cut in half to form two thinner boards. A table saw was used to cut half-way through the board vertically. Then the board was flipped and cut again to create the two thin boards.
Although this method resulted in two remarkably smooth boards, both boards were still planned to around 3/8" to remove any surface imperfections.
Next, the deck boards were cut to length with the ends being angled slightly. At the rear of the sled the central box is slightly longer than the side rails. This angle on the ends of the deck boards creates a nice transition between the side rails and the end of the central box.
With the deck boards cut, they were aligned on the frame and the position of the mounting holes were transferred to them using a hand drill. I then used my friend's drill press to finish up all of these holes in the deck boards. With these holes drilled, both deck boards were bolted to the frame using 1/4" screws.
Two 1" x 1" side rails were also ripped from a 1" piece of cherry. After rounding the edges of these rails with a router, I aligned them onto the frame, marked the location of their mounting holes, and drilled these holes through the rails.
All of the wood on the sled - including the handlebar - was finished using danish oil. I initially was going to use a finish like polyurethane, but given time restraints I decided to use oil instead. In the end I think this was a better option as the wood will be exposed to a lot of moisture, which could work its way under a hard finish. The oil may not hold up as long, but I can easily re-apply oil at any point in the future.
Step 9: Mount the Skis
My friend found some old 135cm skis in his shed. Not only were these skis the perfect length for my sled, but they had a sidecut to them, which I thought would help with the steering. I positioned the skis under the shoes on the frame and marked the location of the mounting holes onto them.
Next, I drilled pilot holes in the skis for the mounting screws to thread into. I wanted these holes to be as deep as possible without drilling through the bottom of the skis. To make sure I didn't drill too deep, I wrapped a piece of masking tape around the drill bit at the correct depth. Once the masking tap began brushing the surface of the ski, I knew the hole was the correct depth and I stopped drilling
With the skis prepared for mounting, I painted them red. I like red skis as it reminds me of old-time flexible flyer sleds. You'll notice that I also painted a set of straight 135cm skis that I have - although I have yet to try them on the sled.
After the paint dried, I cut the mounting screws (I used #14 stainless wood screws) to length and attached the skis to the frame.
Step 10: The Steering
With the skis attached to the sled, it was time to finish up the steering system. First, I cut the two brackets for mounting to the skis from a sheet of 1/16" aluminum. I drilled a 1/4" hole through each of these pieces close to their one end.
Next, I used my bending brake to bend this sheet into the final u-shaped bracket. As you can see, I was barely able to make the second bend with my brake. Notice that I've also drilled two small holes in the bottom of the bracket for mounting to the skis.
Once the brackets were bent, I used the hole in the one end of each bracket as a guide to drill the hole in the second side of each bracket. Obviously a drill press would be ideal for this, but I don't currently have one at home so I did it carefully by hand.
These steering brackets were mounted to the front of the skis using the same technique and screws that I used for mounting the skis to the frame.
Moving to the handlebar, I inserted two 3" long 1/4" screws through the angled holes. I used countersunk washers and screws with countersunk oval heads to account for the angle where the screw heads contact the handlebar. Inverted lock nuts and countersunk washers were used to fasten the bolts into the holes on the top side of the handlebar. Additional inverted lock nuts were added close to the ends of the screws. These nuts would be used to fasten the inner tie rod ends.
I fastened tie rod ends to both of the steering brackets using a 1/4" bolt and many washers. These tie rod ends have a 1/4" female fine thread socket for attaching to the tie rods.
With the tie rod ends attached to the brackets, the tie rods were threaded into them, the inner tie rod ends were attached to the rods, and then these rod ends were slid over and bolted to the tilted bolts.
Step 11: It's Testing Time!
With the sled finally finished, I took it out to some no winter maintenance roads in Pennsylvania and Vermont. On our first day of testing, we learned that the skis had a tendency to flip up-side-down during turning.
To fix this, we made some small aluminum stops, which would prevent the skis from tipping beyond approximately 30 degrees.
This worked well for a few runs, but eventually the stops ended up bending and breaking the very thin control arms they were attached to. I re-built the control arms out of thicker aluminum and with integrated stops to prevent ski flipping.
With the control arms fixed, my wife and I made the 6 hour drive to Lincoln Gap in Vermont. This time everything held together beautifully and I was able to record a maximum speed of 34 mph! However, the sled had a tendency to catch the edge of the outside ski when coming out of a corner. I felt like it was trying to toss me off the side - although it was never successful. I determined if I could always keep the skis in a negative camber configuration this situation would be avoided.
After receiving a final late winter snow storm, I tested this negative camber configuration on a mountain close to home. It worked as expected; I did not catch an edge and the sled still turned acceptably. The steering is still not quite as sharp and responsive as I would like, but that gives me something to work on for next year. Be sure to follow me here on Instructables or on Youtube if you want to find out how I end up improving this sled in the future.
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