Video demonstrating our first experience of The Relaxitrator's inexplicable attraction towards lamp posts. (Note: Has some speed-induced swearing)
We only have photos of the complete sled but the assembly process is simple enough to explain.
A pair of old skis
An office chair
Some rough-grit sandpaper
A Hand saw or chop saw for cutting 2x4's
A Hot glue gun
A Drill bit about 1/4 the diameter of your screws for predrilling
~30-40 Screws (we used some drywall screws we found lying around but this is definitely not optimal)
Step 1: Prepare the Runners
Remove the bindings from the sacrificial skis.
Cut some 2x4s to the length of the chair seat.
Drill the 2x4s into the skis where the bindings were. (We used 2 layers of 2x4s because we were concerned about snow clearance)
Make sure to drill the wood to the skis very securely - this is an important joint. To prevent spliting, be careful to leave enough space between the screws (about 1 1/2 inch) and always predrill your holes with a thin drill bit.
Step 2: Prepare the Seat
Remove the wheelbase from the office chair. This should be fairly simple - the metal wheelbase usually is screwed into the bottom of the seat four points.
Step 3: Attach the Seat
With our chair, we were able to remove the seat cushion to get at the structural material of the seat. The stiff material of the chair may be MDF if the chair is old, or some hard plastic if it's newer. Drill pilot holes in the seat where you plan to drill it to the 2x4s attached into the skis. I'd recommend screws about 1 1/2 inches apart down the whole side of the seat. This is an important joint, because it will take a beating when you hit jumps and get mad air.
Step 4: Install Foot Braces
It makes riding a lot more comfortable if you have blocks at your feet. They help you stay in your seat. We just screwed blocks of wood into the skis near the front, but this is tricky because the skis are so thin this far forward.
We started with a piece spanning the the skis to rest your feet on, but this quickly broke when the sled found itself mysteriously attracted to this lamp post on one fateful ride (see photo). After this, one of our foot blocks broke completely off. If you can find a better way to attach blocks here you should use it. Epoxy, hot glue, screwing from below...
Step 5: (Optional) Grip Tape
We quickly disovered that standing on the back of the sleigh with your feet on the runners was even more fun than sitting in the seat. From back here, you can kick to add speed, and shift your weight to turn the craft. So we hot-glued some rough-grit sand paper to the skis behind the seat for better grip in intense carving situations.
Step 6: (Optional) Backseat Driver Handles
We installed some handles taken from an old dresser the the back of the seat to give the back rider more control when steering.
When drilling into the seat back be careful not to go too close the edge to prevent splitting, and use screws that are not so long that they poke into your back when you lean into the back cushion.
Step 7: (Optional) Speed Cone and Handle
We added a traffic cone to the back of our seat for its clear aerodynamic benefits (a friend of ours studying Aeronautical and Astronautical Engineering disagrees). It also gave us mad style points when tearing it up on the slopes...* It made a great handle when carrying the sled too. (Make sure to screw it in securely, especially on the bottom)
*Everyone looks good in safety orange.
Step 8: (Optional) Rope Attachment
You can add a way to pull the sled with a rope for convenience's sake.
Drill some holes in the front of the seat using a 1/2 to 1-inch diameter drill bit and put some rope or wire through them to make attachment loops for your rope.
We found pushing it worked fine for the most part.
Step 9: How to Ride
The simplest way to ride the Relaxitrator is to sit in the seat and let gravity take you down the slope. Where will you end up...? Nobody knows... (We did observe, however, an affinity for the sled to be attracted to certain lamp posts and trees...)
For more advanced users, try adding a second person standing on the skis behind the seat. This person can kick to gain extra speed on a slope, or even generate enough power to move on flat ground... At speed, jump on the skis (this is where the sandpaper helps), and shift your weight to cause the sled to turn. Somewhat counterintuitively, you should lean left to turn right, and vice-versa. Shifting your weight back increases the turning effect.
Step 10: More Ideas
Here are some ideas for additions and modifications to the Relaxitrator we and some bystanders have thought of:
A cupholder for beer (or age-appropriate hot chocolate).
Mechanized pedal-treads for reclined uphill climbing.
Team of sled dogs
Onboard sound system
Rocket propulsion through the rear-facing safety cone