First off the warning that comes with half of my Instructables: If you build this or something like this and use it, there are hazards involved, like most things in life. Make sure all materials are strong enough to handle loads.
The Zip Line Swing is a little different to a standard Zip Line. The line is slack and both ends are level. So instead of starting at the high end and ending up at the low end, you start at the middle (the lowest point) get pushed up to one of the ends (high point) and ride it back and forth, like a swing. This makes it relatively more safe in that the passenger does not have to worry about running into a tree, the ground, or a jeep, like you may on a conventional zip line.
I will be entering this into a couple of contest. Please vote, if not for mine, for the one you think deserves to win.
Step 1: Tools and Materials
You will need to gather a few things to make your Zip Line Swing.
1. Cable strong enough to hold the weight of the rider.
2. Rope strong enough to hold the weight of the rider.
3. Wood, for the seat of the swing, strong enough to hold the weight of the rider...see the pattern?
4. Wood glue and screws to make the seat
5. Six Cable clamps the same size as the cable you will be using.
6. A trolley for cable. I used a Petzl Tandem Speed Pulley
7. A locking carabiner that works with your trolley.
8. Some rubber hose to put over the cable to protect the trees.
9. Four lag bolts to hold the cable up on the trees.
10. Two strong trees.
11. Ladder (not pictured)
1. A hack saw or other device to cut the cable with.
2. Jig saw, coping saw, or band saw, to cut a circle for the wood seat.
3. Drill to drill holes into the seat and into the trees.
4. Hobby rasp and sandpaper to smooth the edges of the seat.
5. Wrench to tighten the cable clamps and drive the lag bolts into the trees.
6. A nice multitool. You should always have one.
Step 2: Make the Seat
I used some old oak wood that I had from HUGO. About one inch thick. I have made a few of these types of swings and the best method I have found is to glue and screw two disks together with the wood grain perpendicular to each other to help prevent splitting. I cut out two disks about 11 inches in diameter (about as wide as the plank I had). Glue and screw them together using wood screws long enough to go thru one board and about half way thru the second. The side that I put the screws into will be the bottom of the seat. Drill a hole just big enough for the rope to fit thru.
Step 3: Attach the Cable to the Trees
You should have two big trees. Mine were about 100 feet apart on relatively level ground and were a little over a foot in diameter. I used some rubber hose to put on the outside of the cable, to protect the trees. Used three cable clamps per end. All the cable clamp nuts should be on the load side of the cable. Do not over tighten the nuts. Cable clamps deform the cable and over tightening can damage and weaken the cable. I assembled everything near the ground and then slid it up the trees, slid it down, made adjustments and then slid it back up, multiple times until I got it just like i wanted.
Step 4: Attach the Swing to the Cable
The swing is assembled by tying the rope to the carabiner, I used a double figure eight on the bite with a safety knot. The other end of the rope passes thru the wood seat and you tie a knot on the bottom. I tied a simple overhand knot to be able to make adjustments to the height. Once I was happy with the height I tied a few more overhand stopper knots. The trolley is placed over the cable and the carabiner is locked onto the trolley.
Step 5: Test
If you are brave jump right on. If you are smart strap on something heavy, like a few bags of concrete and test it out. Try pushing and launching from both directions, bouncing, swinging. Make sure it can hold up and will be relatively safe to ride. Make sure there is clearance from other trees and the ground. Double check the cable, clamps, rope, trees, everything. Then try it yourself. Once you are confident, you are ready to let the kids have fun.
Step 6: Launch the Rider
Have the rider sit on the wood seat and hold onto the rope. Push the rider up to one end of the cable and let them go. If you have built everything right, they should slide down to almost the other end and then back to the middle. Start new riders on shorter runs and only build up to the maximum run when they are comfortable. Which was the second ride for my four year old that thinks her middle name is "Dangerous". Make sure riders know to hold on and wait for help getting off because the loaded cable could pull the seat up, if they jump off. Also make sure bystanders know to stay a safe distance away.
As always, Enjoy.