The Ballista

Back at it again.  I’ve started winding up a brand new set of springs in three strand nylon.  The last lot were spliced and not perfectly matched in size.  Mainly, they were just to test the new Sherlock Holmes anti chaffing gear.  No worries on the chaffing front now;  I hope.   No worries at all …… right?

Part of my misspent youth was done at Dad’s workbench using this particular hacksaw.

Dad had brought this tool to the States with him back in ’65.   It resurfaced recently and gave me a major flashback as  I hadn’t seen its familiar shape in forty years or so.  When I was eleven years old and running wild in the woodlands of Berkshire,  I was introduced to metal work by using this saw to cut off short chunks of half inch steel bar.  Two shillings of pocket money each week, could buy enough hacksaw blades to produce scores of these heavy  slugs.    When they were loaded into my slingshot (catapult in Brit speak) these cylindrical “glandes” proved instantly fatal on the big Norwegian rats that were doing a booming business over at the Bracknell rubbish tip.  Back then we little savages were not particularly squeamish about animal rights.

Almost half a century later, rather than helping to bump off vermin, I find myself using this same hacksaw to cut parts for Firefly.  The more things change, the more they ………

……..  well,  probably the rats stayed the same too.

……..She’s back.   8 shots today.  All were done with the same 7,000 grain bolt fired into our new earth berm.  Zero damage to the bolt,  so it looks like we may finally have solved the backstop issue.  Velocity is close to our old standard 300 feet per second.  More detailed  testing will have to wait until next week when business type work slows down.

The upgraded, spring steel  kamarion is working very well.    Looking down from the top (plan view) we can see that the  kamarion is deliberately bowed towards the front of the machine.

This deflex shape in the at rest position,  gives the kamarion  some preload to help resist the field frames that want to turn inwards under the draw weight.   At 5,000 lbs. of pull,  the deflex disappears and the kamarion straightens out.  If the kamarion was straight when there was no load on it,  by the time full draw was reached,  it would take on a reflex curve pointing towards the back of the machine.  This is exactly what happened before the last upgrade, and it eventually led to torquing the field frames out of shape.   Looks like we may have dodged that bolt this time.

Sometimes it is not the best idea to let an old man near a spade.  There is no telling what they might dig, or how deeply,  if they ever get together.  At least, so says the Rebecca,  after seeing what had happened to her view from the porch this morning.  Here is what all the fuss is about:

A measly little slot in the ground 60 yards away, where a fella can have some hope of catching his ballista bolts without having them shatter all over the place.  Fortunately  I’d just completed Dear Wife’s, bear proof (we hope) composter, and there are brownie points to squander.

My salvation.  The twin, turbo composting pickle barrels in action.

But seriously,  having a gentle backstop is going to be vital for the next stage of accuracy testing.  I plan on making  a simple wooden  frame and hanging a big sheet of cardboard from it to use as a target.  The relatively fragile fins should pass on through the cardboard unharmed, and then the bolt will have a nice soft earth berm to burrow into afterwards.  Sounds perfectly lovely, doesn’t it?

The price of “progress” always seems to involve punching holes in the view.    If they ever get around to lining up the usual suspects for this crime,  I am told that old men and their hardware will top the list.

This time I have a more cunning plan to defeat the chaffing trolls.  Five wraps of  heavy Dacron upholstery fabric now protect the precious nylon rope from abrading away under the immense pressure from the steel crossbar.  The point of failure in the previous set of all leather wraps appeared to be at specific pinch points located at the ends of the crossbar.   The juncture between the crossbar and the vertical ear was able to  grab the soft suede and then elongate it to the point of ripping.  After that, the nylon rope was able to pop through the tear and make direct contact with the steel.   That was all the invitation those little nibblies needed to start munching on the spring.  They don’t really come out of hiding until the linear tension on the spring is at its highest.   If Firefly only engaged in low power shooting,  it  wouldn’t be a problem.

When we get around to trying springs made from nylon thread,  rather than the 3 strand nylon rope we are currently using,  I’m thinking the first few layers of thread contacting the steel will probably get eaten through.  I suspect that the resulting shredded fibers may serve to protect the rest of such a spring and perhaps obviate the need for all this fancy anti-chaffing gear.   With 3 strand, if one of the ropes  pops under the load,  it compromises the  linear tension in the spring and throws off the balance between the two halves of the machine.  Very uncool for anything but rudimentary shooting.

Not only is this new fabric highly tear resistant, but I suspect that having multiple wraps that can slide over one another, will also help to defeat any pesky pinch points.   The chamois leather outer wrap is really just for aesthetics.  It wouldn’t do to have Firefly looking like a tweedy something salvaged from Sherlock Holmes’s wardrobe.

At the time of installation, I was able to slip some heavy steer hide collars around the crossbars and up against the slotted ears on the washer assembly. This, and the new fabric wraps,  seem to be an obvious improvement over  previous attempts.   If I were not philosophically opposed to soppy storms of regret,  those earlier versions would be prime candidates to weep about.

No need to blither on about this anymore.   It’s all really quite elementary, my dear Watson.

…as requested.   Smoothy McSmooth rides again.

Compared to wimpier version below.

A last hurrah for all that bloody grinding.  Here’s a shot that includes the fattened stanchion.

Stay tuned for upcoming episodes featuring fast nasty things.

*  Richard III,   Act I,  Scene I

No dark meaning in the title to this posting.  It’s just that at 9.00 o’clock this morning I found myself with a shadow on the ground, camera in my hand, and Little Richard playing on the radio.  Naturally the Bard had to step in.   And here we are,  stuck with another full round of Shakesperian  gibberish for the rest of the day.  Got to love the melodrama of a shot like this.

Finally out of surgery and convalescing in the sun, Firefly shows off her muscular new kamarion.  The addition of the 5/8″ thick spring steel backing has turned this kam into a gigantic tuning fork.  With a sharp rap it will ring for a couple of minutes if the ends are allowed to hang free.

A few hours of light grinding and finish work,  and Firefly will be ready to have her torsion springs put back in.  Can almost hear those bolts thumping into the backstop now.

… Or in pig Iambic Pentameter,  “The mind’s earshot can hear a bodkin thud,  We  pray this project’s not some grievous dud”

Oh brother! …….. see what I have to put up with.