A chronograph has been ordered and with a bit of luck some data should start flowing in late next week.  The first set of limbs developed a crack in the first field test and have been drastcically reinforced with a spring steel brace, cross-bolted through to a backing plate.  For safety, seat belt webbing has been epoxied onto the back of the limbs and if that doesn’t prove strong enough to stop the limbs fracturing, it should surely be enough to guard against any unpleasant trajectories.  A more authentic set of limbs with a set of full length steel braces and steel hooks for the bowstring will be made later when we have a better idea of all the forces involved.  The second field test will be at noon tomorrow.  Their will be two objectives.   First, to test the power from the point testing ended in the first test, and then continue on testing through to full draw.  Perhaps five or six shots should accomplish that.  Second, to measure pull weight at each power level.  Now that I think about it, there is no reason those tasks cannot be performed concurrently……..  what a good idea.

The spring steel brace, visible when the chafing pad is lifted up.  Not visible are the 3/8″, grade 8 bolts that go through the thickest part of the limb to the backing plate on the other side. The deep concave depressions in the limb serve to keep the  bundle of spring cord in place and prevent it from splaying out and causing clearance issues with the field frame.  They also help stabilize the limb by giving the spring bundle some controlled surfaces to grip against.

And with the pad down.  Note the heavy leather strips that form a buffer where the limb will contact the stancion on the field frame.

Jig for winding the torsion springs.  Note the seam of stiching at either end of the bundle.  This was needed  to hold the cords in place during assembly into the field frames.  The other approach would be to thread the 275 feet of 1/4″ nylon cord around the crossbars and through the holes in the field frame.  A profoundly tedious process.  I may try it someday to gain a more tightly wrapped spring with a minimum amount of spiral.  For now, the jig approach will suffice.

Sometimes what you started has a way of catching up with itself, making whole something that before you started , never was.  I wonder if this is what having a baby is like.

One Response to “sometimes what you started”

  1. Sarah Coburn says:

    The gestation of The Ballista will have similar metaphors to the gestation of a human. There are “limbs” being formed and if something is not quite right in it’s development, as in a mutation, the body and or the “creator” has a unique and “sure-fire” remedy that will ensure the survival of it’s off-spring. The comparitive I struggle to see is the moment of the actual birth. I can see it’s conception, my father’s mind on fire, teaming with ideas, ingenuity and having Aha! moments. At what point is or was the umbilical cord cut? Does this little ballista have a name?

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