The Ballista

I checked all areas on these Mk IX irons with a few file strokes to confirm there were no hard spots. They appear to be tempered to a nice spring grade.

The square hole is 1/2″ X 5/8″. It is intended to anchor a tension strap made of Dacron strands. Not only will this new arrangement be lighter, the strap should also be stronger. While it is true the previous strap was made from kevlar, it is also true that it was in the form of webbing. I imagine webbing to be less strong of a format because so many of its fibers run crosswise to the strain. Our new attempt will have all the fibers running lengthwise. And quite incidentally, their whitey/yellowish colour will do a fair job of mimicking sinew.

Not that we care about that, right?

With the Mk. IX limb irons finished and ready for installation, all that’s left is to figure out the woody bits. Specifically, the relative superfluousness of that area marked in chalk on the old limb. There might be 10 fps hiding in there.

My gut tells me to go all in here and thin out the tips. What’s the worst that can happen. Replacing the limbs in the event of failure is a minor chore compared to making the irons. A woody bit goes pop! So what? Maybe we learn something, eh?

Anything for speed.
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Don’t worry mother. Civilians are banned from the area during testing.

These sporty new limb irons, the Mk IX’s, weigh 2 1/2 lbs less than the previous Mk VIII’s. At four pounds each, they feel noticeably lighter than those 6 1/2 lb behemoths that Firefly has been hauling through the sky in all the recent testing.

These beauties have been heat treated to 40 RC. If you hold them lightly and give them a sharp rap with a hammer, they’ll sing to you for a good twenty seconds.

The welding of the seam on the Mk IX’s went off nicely with the Tig welder. The chalk marks represent the final version of what what will be half-depth lightening cuts. This will still leave 1/8″ of material at the bottom of the depressions.

While a couple of tapered tongues could have been neatly forge welded together to form the U-strap, here at the LCF we try to keep our standards of authentic portrayal within the bounds of certain key questions. Things such as: how accurate? how far? how fast? how powerful? And the like. The smaller niceties of metalworking are more useful to us as accomplished entities, rather than unaccomplished diadems sparkling with the promise of 4th century metal working techinique. It is enough that the designs chosen here would be as equally feasible with a well equipped and well staffed black smithing operation, as by yours truly with a bunch of whirling electrons and hard tipped carbide.

A few of my staunchly anti-weapon-of-anykind friends may be tumbling to some subversive implications they find buried inside our little project. Razor-tipped insights like, “Firefly is underlining the futility of weapons development in a world run amok with arms production”, have broached my inbox. At the very least, she is an “absurd anachronism, as much to be laughed at as reviled”.

The horror of their fascination is a marvel to behold. What exactly did they expect the “End of the World” to look like? Predator drones and high-fructose corn syrup are just how we get things done in the 21 st century. What’s next? — phasers and soylent-green — I guess those two were always the natural extension of stone knives and bear meat.

Their accusation of “anachronism” stands. Guns and butter are getting to be kind of old school these days.   Most folks lost their taste for catapults and yogurt millenia ago.

The two halves of a Mk. IX limb iron, come together for their first meeting.

Good weld prep and pre-heating will be needed before Tig welding that seam. The steel is 4130 and, just like before, it will eventually be heat treated to around 40 RC. When they are finished, these irons promise to be 38% lighter than the previous set that weighed 6 1/2 lbs each. As seen in the above photo they tip the scale at 5 lbs. The anticipated lightening cuts should take that down to 4 lbs. How much that might improve velocity is an open question. If it will squeeze out another 50 fps, I promise to do cartwheels all the way down the catapult range.

Implement to one 1/2 of wall thickness. Design similar lightening cuts for u-strap. No cut-outs over weld seam.

The outside half of one of the limb irons has put comittment behind our dithering. In short, cuts have been made.

I suppose it is the nature of a journal, or a diary, or in this case a blog, to appear to be repeating itself. This seems like the umpteenth time I’ve shown this style of limb iron in manufacture. But, it is no good trying to dodge the nature of this beast, so here goes:

The Mk. IX limb irons have recieved their major bends. Next we will trim them for profile and then weld their two halves together.

As always in this project, even though we do use some modern methodologies like Tig welding and machining to supplement our forge work, there is nothing in the basic design that would be anything but easy for a full on blacksmith (ancient or not) to reproduce.

The irons for the MK IX limbs have been cut out in flat pattern, and await the tender mercies of the forge.

It used to be that making up new limbs for Firefly was a traumatic mental experience for yours truly. How heavy is strong? How light is weak? It is not like there are any dynamic calculations going on here. Well, not of the math kind anyway. This is all guaged for strength by eyeball.

It tickles me to think these particular “calculations” were tackled by the original makers of the Orsova machine. Part of the appeal of this discipline is that it makes Firefly a time machine of sorts.

And so, I meander over those final cuts in my mind.

Trims that make us lighter, can also have a weakness when taken to extreme. It still pays to OK (overkill) in certain areas.