The cheiroballistra arms consist of two pieces: wooden cones and steel hooks. This article describes one way to forge the steel hooks from round steel bar. If you have rectangular steel at disposal, the process is simplified a lot.
The process step-by-step Edit
Start by heating two pieces of round steel bar; you will be forging and heating the in alternation:
Heat a section of the round bar and forge it rectangular, then move on to the next section. Repeat until the whole bar is roughly rectangular:
Unless you did a really good job on the first run, you probably need to reheat the entire bar and finish the job with light, careful strokes. The resulting bar should be fairly uniform:
Next forge a length at the ends (i.e. hooks) round:
Heat the rounded parts and bend them into hooks. If you want uniformity, forge the hooks around a piece of round steel bar or a pipe:
Attach the bar into a vise with the hook protruding about the jaws:
Use whatever means you have at your disposal (e.g. a pair of pliers) to bend the hook 90 degrees backward:
If necessary, finish by cold-forging the arms perfectly straight.