When made properly the rope is about as strong as 3/8 nylon rope.
To do this tutorial you will need:
1. Plenty of plastic bags
2. A knife
3. A three strand rope making machine. You can make one out of bike parts, wood, or get an old one off ebay.
4.A paddle with three arms - a crucifix will do
5. A spinner hook
6. Two or three people. One at each end and one in the middle is best.
Step 1: Cut Your Plastic Bags and Make a Daisy Chain
It takes about 4 regular sized shopping bags to make a foot of rope.
I've scavenged most of mine from the grocery store recycle bins. choose stronger bags if you can find them. Bigger bags don't work as well with this method.
The bags I use have a seam down the sides. Lay them on a cutting board in a small pile and cut down the seam. Be careful not to cut the bottom of the bag or it will be much weaker. You should now have a peice of plastic with a loop at each end. When you have cut enough bags you can loop the handles through each other to make a daisy chain. you shouldn't have to tie any knots, but if a bag breaks for some reason it's not a big deal to tie it.
If you can't get a good supply of bags with the seams on the side try poking a hole in the side, near bottom of the bag instead of cutting them down the middle.
If you're not using your chain to make rope right away wrap in in a spool around a stick to keep it from getting tangled.
Step 2: Roll Out Your Lines of Daisy Chain Where You Are Going to Make Your Rope
Find a space that is a little longer as the rope you want to make.
This rope maker has three hooks, some have four or more.
Attach the rope to one of the hooks (hook A on the diagram) on your ropemaking machine and roll out a line of bags for a little farther than the rope you want to make. Try 10-15% more. Loop this first line around one arm of your paddle, which should also have three arms. Bring this line back to the rope making machine and loop it around the next hook (hook B) moving counter- clockwise (or clockwise as long as you're consistent). Bring that back to the paddle and loop it around the next arm moving clockwise. Continue going back and forth until you re-connect to the hook you started with. Tie the end of your rope to the beginning.
Once you have laid out the strands take the three loops around the paddle arms and hook them onto one hook that will spin freely.
Step 3: Start Twisting the Rope
You'll have to twist the rope a lot.
All three of the hooks spin the same way. your six strands of plastic will twist into three pairs.
Pop any bubbles that form. Try to get the strands to twist with an even tension down the whole length. It's good to have enough tension in the lines to keep them off the ground, but not completely taut or they will break. At this point the lines are still weak and vulnerable to stretching.
Step 4: When the Strands Are Twisted Enough They Will Begin to Come Together in a Counter-twist
Use the paddle to keep the lines separated. As the rope begins to spin together you can slowly inch the paddle towards the rope making machine. Move the paddle slowly enough that the rope forms tightly, but not so slowly that the lines break.
Try to keep a steady tension on the rope between the paddle and the spinner hook as it forms. Between the paddle and the rope making machine the lines don't need as much tension. Occasionally move the ends closer together to relieve tension.
Once the paddle gets to the end you can take the lines off of the hooks. Continue to spin each line separately so that the remaining line twists into rope. This takes three people. You can then splice or burn the end to finish it off.
Step 5: Stretch Out the Rope to Set the Strands.
Tie each end to a tree and lean your weight into it. Here the rope is doubled up because we didn't have enough space, but it's not necessary.
you now have rope from plastic shopping bags!