Step 3: A Call to Arms
In the last step we made several cuts which will now allow us to mold visually appealing and functional arms for our chair. You will find that polyethylene is much like steak, in that it is easier to work with after the proper application of fire. OK, technically you can use a heat gun here, but using a torch seems more manly and raises the opportunities for catastrophic failure exponentially. The important thing here is to heat the plastic until it is malleable and to bend and then form it into arms. There is a certain amount of art to this as the temperature where the plastic becomes "shiny" and really easy to form is not too far removed from the temperature where it bursts into flames. Since the last thing we want to do is release harmful chemicals into the air by creating a mass of burning plastic, this is a time to take things nice and easy. It is also a good idea to use proper safety equipment (welding gloves, goggles, etc.) and to have a fire extinguisher close at hand.
The first bend we want to make is at the front of the chair. Remember those little 2" tabs we created at the end of the last step? Well, now we want to bend them along that two inch line. To do this we gently apply heat to both sides of the area until the plastic begins to "shine" at that point, take the heat away and hold a piece of flat steel behind the tab to make a sharp bend, hold the tab in place until it cools enough to keep it's new shape. Repeat on the other side.
Now we are going to form the top of the arm. This time we are applying heat over a much larger surface, so take your time. As soon as the "arm" begins to bend go ahead and force it into place, holding till it cools. It is not important that it be perfect at this point.
In the picture below, you will see a bolt that is holding the arm top to the arm front, it is time to install that bolt. Force the arm into place and drill a 9/64" hole through both pieces. Thread the bolt though and attach with washer and nuts.
Now that the front is attached, continue to heat the arm and form it until you are pleased with the shape. This is also an opportunity to put some nice touches, like the front corner fold in place.
Once you are happy with the general shape of your folds it is time to cut the arms into a pleasing shape. We chose to freehand a nice shape on one and then use the cutaway as a template to repeat the shape on the other arm. You should do that too, unless you are some kind of rebel.