11-18-2012, 08:40 PM
Robert,
Most interpretations have the curvature being carved rather than bent into the beams. If you have the capability to steam and bend such substantial timbers it would be interesting to see the result. It would certainly give more ground clearance for the spring and the end of the arm which extends through it. An added benefit is that the beams could be somewhat lighter. You will just have to be very careful with the placement of the crossbeams which will act as stanchions do in other torsion engines.
Steam bending is just the thing for bending the distal portionn of the arm. Other than finding a grown-bent timber of the right dimensions, it seems like the most practical method. I would suggest using a section from the outer edge of a log with the bark carefully stripped to avoid grain violations. This is how bowyers make bow staves that don't split under tension.
When it comes to the choice of iron or bronze for the washers, you might consider the use of wooden washers like on the larger two-armed ballistae that the onagers seem to have replaced. Since there is only one spring there is no need to balance the tension by adding or reducing twist. The real power comes from the initial tensioning. At very high stringing tensions additional twisting becomes a self-defeating exercise. Supposedly, it causes the bundle to bunch up and reduces the springs responsiveness.
The rest of the hardware should be very simple since no fasteners other than the spring rope are mentioned or needed to hold the frame together. The only iron parts I see necessary are the collar and pin for the sling, the trigger/latch, and maybe a bent-hairpin shaped piece lashed to the arm at the bend to reinforce it and froming a ring where the trigger can be connected (see attached drawing).
Good luck with your project. After figuring out the bent-arm solution for this machine, I've gotten side-tracked working on similar revisions or all the other Roman weapons. I really need to get back to this though.
Most interpretations have the curvature being carved rather than bent into the beams. If you have the capability to steam and bend such substantial timbers it would be interesting to see the result. It would certainly give more ground clearance for the spring and the end of the arm which extends through it. An added benefit is that the beams could be somewhat lighter. You will just have to be very careful with the placement of the crossbeams which will act as stanchions do in other torsion engines.
Steam bending is just the thing for bending the distal portionn of the arm. Other than finding a grown-bent timber of the right dimensions, it seems like the most practical method. I would suggest using a section from the outer edge of a log with the bark carefully stripped to avoid grain violations. This is how bowyers make bow staves that don't split under tension.
When it comes to the choice of iron or bronze for the washers, you might consider the use of wooden washers like on the larger two-armed ballistae that the onagers seem to have replaced. Since there is only one spring there is no need to balance the tension by adding or reducing twist. The real power comes from the initial tensioning. At very high stringing tensions additional twisting becomes a self-defeating exercise. Supposedly, it causes the bundle to bunch up and reduces the springs responsiveness.
The rest of the hardware should be very simple since no fasteners other than the spring rope are mentioned or needed to hold the frame together. The only iron parts I see necessary are the collar and pin for the sling, the trigger/latch, and maybe a bent-hairpin shaped piece lashed to the arm at the bend to reinforce it and froming a ring where the trigger can be connected (see attached drawing).
Good luck with your project. After figuring out the bent-arm solution for this machine, I've gotten side-tracked working on similar revisions or all the other Roman weapons. I really need to get back to this though.
P. Clodius Secundus (Randi Richert), Legio III Cyrenaica
"Caesar\'s Conquerors"
"Caesar\'s Conquerors"
