The Ballista

I finally got around to dissecting the starboard bundle to see what might have caused one of its 1/4″ nylon lines to break.  A few snips on the stitching allowed the anti chaffing gear to be removed.  The hole that was discovered in the suede,  lined up exactly with the broken three strand nylon line.  Cool.  This is all very fixable.

I did wonder at the time the springs were installed if I shouldn’t use some heavy leather inserts for additional protection over the crossbars.  Well duh!

Also on the “duh” front, I do remember having a punch slip and puncture the soft leather covering.    I let it go at the time because ……

……. well because  I’m a lazy twit I guess.

Standard operating procedure in our mold shop these past 30 years has been to take a big block of metal and cut away all the parts of it that are not wanted to form what is.  A purely reductionist scenario that leaves a big pile of metal chips and swarf, always thirsty for human hemoglobin.  Now, in this welding adventure on the kamarion, I find myself using a softer strategy.  With TIG welding it is possible to create more by building up rather than just taking away.  A blob here, a bead there,  welded in  chunks all over the place; it really is quite organic.  No blood either because everything is cauterized.

If I can stand the high argon bill,   this is an interesting approach to reassembling the molecules.

(Note to self:   Flow with the gas dude.   It is all about matching volume and flow.)

Hey! it was dear wife’s idea to add the the.  It just sounds so much better in public than  “my little commandant”.  Thanks for the tip Basil.

Dark and dangerous, the Rebecca has been known to eviscerate male egos with the mere cock of an eyebrow.  So glad she’s on our side.

There really is no point in having a time machine if you can’t have fun with it once in a while.  The Rebecca spied my partially finished kamarion and declared it somewhat cartoonish looking.  Good for her, too.  A few jolts on the chin are always welcome when one is this deep in Acme’s garden.

Besides, it seems like a perfectly valid point.  The whole thing does kind of resemble an implement Wily Coyote might pull out of his bag of tricks.   In terms of modern usefulness, about on par with the hollowed out log Fred Flintstone used for a car.   I tried to assure her that the kamarion would eventually return to a more serious demeanor.  As much as a hunk of iron can anyway.

I think I got the benefit of the doubt on that one.  Yabba daba do.

Firefly gathers her strength for another round of inquiries into our favorite mystery.  I probably have about three weeks of solid work before she will be ready to do some distance shooting.  A stand has been designed, but it still needs to be made and tested before we can go on any field trips.

The great privilege of projects like this is that one can say a thing, and then go ahead and make it so.  It is a kind of freedom hard to find these days.  The looseness to create, unfettered from the old tick-tock in the corner.   I am very lucky to get to do all this goofy stuff.  My father left this world, denied these sacred pleasures by the debilitating effects of Parkinson’s.  Time is the ultimate warden, and our playground inevitably shrinks with age.

Thank you,  people that offered their condolences.  Our family is grateful for your kind thoughts.

Today I will do some welding on the kamarion.  Not, however, until I’ve had my breakfast.   The Gods willing, there are any number of broccoli porridge surprises yet to be consumed.

My father, John Watts,  passed away yesterday at the age of 81.  He had suffered from Parkinson’s for the last fifteen years and the news was not unexpected.  Dad was very proud of his work as lead engineer on the Boeing 777  landing gear.   A couple of years ago we visited the Boeing Flight Museum, and to our surprise they had a full display of his design.

Dad did not have a formal education as an engineer.  He was just an exceptionally gifted designer, and Boeing snapped him up in the great brain drain of the 60’s.  During World War Two he was a part of the Home Guard in Somerset, and served an apprenticeship in the Westlands plant working on Spitfires.

Cheers Dad.  Your wheels have finally left the ground.

The Chevy coil spring has been forged to hug the back of our old mild steel kamarion.   Next it will be Tig welded in place.  At this stage,  cutting the kamarion in half allows the tangs to fit  into the field frames without any undue stress from possible misalignment.  An 8 inch long  piece of  4140 at the the top the arch, will create a strong weld splice when we are finally ready to rejoin the two halves.

I remember that at the start of this project I had to decide what material to make the field frames and kamarion from. My final choice was to use mild steel, thinking it would be a viable substitute for the  wrought iron assumed to be used in the original.  By taking this lower grade approach, we now know enough to ask and answer certain questions about the artifacts that never would have arisen if we had used top grade materials from the start.  Was the  original Orsova ballista made to run with draw weights in the 5,000 lb class?  As can be seen from the most recent rounds of testing,  the stanchions and kamarion would need to be made from tempered carbon steel to hold up to that kind of draw weight.   Short of that,  mild steel or wrought iron for these parts is only reliable up to 3500 lbs or so,   and that would imply a machine of much less potential power.

Whatever the metallurgical truth may be about the Orsova artifacts,  the current upgrades on Firefly seek to prove  that, if the materials and workmanship were held to a high standard,  the basic Orsova geometry could have been sound for a steady diet of 5,000 pound pulls.    Given our previous caveats, this likely means that the Roman machines were  capable of generating 2000 or more  foot pounds of muzzle energy,  the same level Firefly was starting to exhibit a few weeks ago.

A number of people have sent in suggestions, that instead of obsessing on brute force,  the performance may be improved by lightening and shortening the limbs by a couple of inches. These are good ideas and eventually we will try these tweaks to the design.   However, at this stage, it is important not to settle for too low a draw weight in order to accommodate inferior  hardware.   It is really all a matter of balance; creating a mechanism where no one component is more likely to fail than another, and then running the machine within strict and prudent limits.

For the adventuresome, that translates into a 5,000 lb. playground.   When we get there, tweaks will be inevitable.

Save for the grind and finish work, the upgrades on the field frames are completed.  The Hi-test weld that has been added to the outside of the curve on the stanchions,  has caused this part of the field frame to exceed the dimensions of the original as depicted in the Baatz drawing.  So far this is the only variation from the Baatz drawing we have allowed.  If our field frames had been made from something tougher than mild steel, this increased girth would not have been necessary.  In this fuzzy area it seems appropriate to use our guiding principle of trending towards maximum performance.   The safer assumption appears to be that the original Orsova ballista probably had all of its critical parts made from tempered carbon steel.   Anything less  runs the risk of underestimating Roman metallurgy as it would have been applied to one of their high end products.  Not a safe bet at all I should think.

I had expected to use a new piece of 4140 rectangular bar to upgrade the kamarion.  As it turns out,  it seemed better to save that piece of material for another part of this project.  In its stead, work has started on straightening out an old Chevy coil spring.

The plan is to continue forging this 3/4″ diameter piece of spring steel into a backing, and then  Tig weld it onto the current mild steel kamarion.  The final version should be close to the cross sectional dimensions represented in the drawing by Aitor Iriarte  (See posting titled  “The paper”).  The kamarion we have been using to date, was based on the Baatz drawing, which is notably less tall in cross section than the Iriarte version.

It occurs to me that the astute reader may wonder why I have torn Firefly apart after recently announcing, ” The bundles have settled. Consistency at last”.   The reasons are twofold.   First, now that we have pretty well established that this machine has impressive levels of power, the next task will be to revisit the whole question of shooting precision and accuracy.  The only way to get to that,  is to improve the reliability of the machine through more upgrades.    The second reason is that in the previous round of testing, the main objective had been to establish that the nylon bundles would reach some kind of equilibrium and not lose velocity with continued shooting.  After we saw a  dozen shots with 7,000 grain bolts maintain speeds of 300 feet per second,  with barely 2% variation, there  really was no logical reason not to tear her apart and move on to the next phase.  …… Which, is where we are now.

Firefly is in surgery for the next couple of weeks.  Thankfully the anaesthesia bill was limited to covering the pain  it caused me as I tore her apart for this new round of upgrades.  This is what comes from having conversations with inanimate objects,  imagined to be sentient.

Below, the starboard field frame gets “the treatment” to banish its case of bad posture,  visible in the photo above.

As convenient as this hot bend fix would have been, ultimately I have to cut the straight stanchion, unbraze the end caps, reforge everything  straight,  weld in a 7 inch segment of 4140 for the  straight stanchion, add 1/2″ of Hi-test Tig weld to the curved stanchion;  and finally, grind and finish.

……When I get done with all this,  it might be a good idea to perform the cleansing ceremony and blow happy smoke over the whole thing to drive out the last of the evil spirits.  With these new upgrades,  our power plants should survive what we have planned for them next.  ……. evil chuckle.