Pi-brackets are one of the simplest components of the cheiroballistra, yet there are several ways to make them. In the antiquity, they were probably forged by a blacksmith. However, nowadays making them is probably easier by simple bending and cutting. This latter method is described below. In either case, make sure that the pi-brackets are long enough so that tenons can be pushed through the field-frame bars and either riveted or bent and thus fixed into place.
Making a pi-bracket bending tool Edit
Start by making a small bending tool. A steel tool will be most durable, but one made from hardwood such as oak will also work well. In either case make sure that
- The distance of the slot from the corner of the tool should be equal to the inner height of the pi-brackets
- The depth of the slot in the tool should equal the length of the pi-bracket's side plus length of the tenon which will be bent inside the field-frame bars.
- For best results the width, breadth and depth of the slot should be just enough to accommodate the pi-brackets.
The steel version of this tool is shown below with some to-be pi-brackets:
Here's an oaken variation reinforced with linen wrapping:
Bending pi-brackets in steel form Edit
Once the tool is ready, insert a piece of steel as wide as the field-frame bars and about 2-3mm thick in the bending device. If you use thicker steel, you have to heat it. Next bend it carefully with a hammer:
Continue by bending it into full 90 degree angle:
Flip the half-formed pi-bracket upside down and repeat the above process:
Bending pi-brackets in wooden form Edit
Place the pi-bracket to the form squeezed between jaws of a vise that prevent it from splitting:
Hammer the pi-bracket into L-shape. As the wood will give in a little, the results will not be as neat as with the steel form:
Now rotate the form 90 degrees and repeat the process to make the pi-bracket U-shaped:
Correcting the angles Edit
Now that the pi-bracket is shaped like the letter "U" (or rather, Π), you can fine-tune the (almost) straight angles in a vise as shown below:
If a pi-bracket is twisted looking from the tenon ends, fixing it is easy by attaching one side to a vise and correcting the situation with a hammer:
At this point you should have almost finished pi-brackets that look roughly like this:
Forming the tenons Edit
The final step is to form the tenon ends. You can use a tool like this to help mark the length of the tenons fairly easily:
Then cut excess material away with a tool that does the job quickly (e.g. an angle grinder or a hacksaw):
After rough forming file the pi-bracket tenons slightly round. You should end up with something like this: