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Below we see application of the linear stretch to the spring bundle.   Above and out of sight there is a two ton chain hoist suspended from the overhead crane,  and on the bottom a forged eye bolt  that is installed in a steel pad bolted to the concrete floor.

3,000 lb of pull with this  set up is enough to straighten out the spring and allow installation of the shim blocks underneath the crossbars.   The next step will be to rotate the washers and apply the torsional preload.  After that we can start very gingerly cocking the machine and trying a few shots.  I am curious to see how well the minimal nocks, seen below,  will hold the bowstring.

Once a final shape is decided upon for the nocks they will be reinforced with an epoxy soaked dacron whipping.  Unfortunately I’m fresh out of cat gut and fish glue.  Darn the luck.

I once knew a man who thought he could steer his boat with a feather.  When the winds were light his technique worked like a charm and he was able to impress a great many people.  However, if ever the wind came up he would be quick to cancel the show.  We all figured he was afraid of hurricanes.

No mater how good your skills at parsing faint wind,  the gains are only measured in survival when things really start to blow.    My muse takes special precaution to make sure she doesn’t get a splinter through the eyeball.

The new limbs were fit into the bundles today to check the  clearances.  Everything looks good.  The  thickened area on the limb iron, where contact with the curved stanchion is made,  does not stand as proud as the detachable version did on the previous set of limbs.  This has the noticeable effect of allowing the limb to rotate perhaps 15 degrees or more past the 90 degree point.  Serendipitous for those that champion a dash of extra twist in their torsion engines.

Refinements are not always deliberate.   If we have the wit to realize them, sometimes they just happen.

Good old inletting black shows the high spots as the irons snuggle down into their final resting place.

The slot in the limb for the biscuit can be seen below.  There will be zero air gap between wood and metal when the irons are eventually bedded with some PC-7 high tensile and high compression epoxy paste.  The limb will be well anchored fore and aft when the epoxy bedding is complete.

I can just hear some nit-picker suggesting the Romans didn’t have epoxy.  If I wanted to take the time to mark and  scrape and fit and mark and scrape and fit and mark and scrape and fit  etc.,  it would be possible to hand work a near perfect fit up between the metal and the wood.  This is something I did countless times in a prior life as a gunsmith.   Suffice it to say that this use of a modern material is within the ambit of our little game.    It doesn’t materially affect the plausible nature of the design.

It has been a furious few days here at the little catapult factory.  Things were groovy, and then I got greedy and thought I could make ’em more groovy by welding on some dang fool  cow bells and whistles to the limb irons.  Long story short,   the execution of these supposed enhancements was, …..  er….. dreadful.  No, I am not going to describe the little horrors  spawned by my own two thumbs.   So,  late this afternoon,  I lopped them off.   (The horrors, not my thumbs.)    Now we are  back to the well executed limb irons originally conceived of at the start of this bout.  Confusing, I know.  Imagine how bad it is for me,  I actually had to act out this insidious pantomime.

In the photo below our good and healthy irons are fresh out of heat treat.   They have been tempered to 50 RC with a nice long sit in the forge  at a  carefully monitored 800 degrees Fahrenheit.   Note the moderately groovy reinforcing biscuits.  Yum.

As the hickory exits the small end of the tapered steel  sockets seen here, the wooden limb (not seen here)  will be constrained to a sectional depth of 3″.  My calibrated eyeballs tell me that, even with hickory, this is probably not deep enough for the really high poundages.  I suspect these irons will allow limbs in the 3,000 lb. class.   In any event,  I shall explore what I can with them before the timber shows signs of getting overstrained.   On the plus side, the limb tips of these babies should be very light  and I suspect they will be good for high velocity, lightweight projectiles, perhaps 4,000 grains or so.

This cow bell and whistle adventure has at least taught me how to make good limb irons.   A cunning plan has been laid to make yet another set more suitably proportioned for heavy draw weights and heavy projectiles.   In the mean time,  I will fit these lighter limbs up and take ’em dancing.  Never can tell who’ll be at that party.

Good job too.    The range beckons.

The trouble with being an enthusiast is that sometimes  zeal can cauterize the mind and seal out better ways of doing something.  To paraphrase Patrick O’Brien, one doesn’t want to be carried away by mere enthusiasm.

Late last night I had a bad feeling about the tapered socket featured yesterday.  While its execution was excellent,  I fretted that it was going to create a hinge point when the limb was under load, and I started to worry that perhaps the limb was not quite deep enough at its base.     The amount of work in making these limbs  pales in comparison to what will be expended tuning them up in the machine and then forever questioning if they couldn’t have been made lighter, stronger and more versatile for testing.    Too bad it took until three o’clock this morning, and in the middle of a dream featuring Rachel Maddow with lots of cow bells,  that I finally figured out what to do.

More later.

My squeamishness conquered, the spokeshave and I had a go at fitting up the new hickory into the irons.  It all went super well.

The bottom face of the socket has a six degree taper to it that matches the limb.  All the shooting  force drives the limb forward, and thus deeper and tighter into the socket.  The weight of the limb is currently at 6 3/4 pounds.  By the time we trim here and add there and trim here and add there etc.,  the final weigh will probably be in the 7 pound range.  To the good,  most of the 2 lb. weight loss over the previous set of monster limbs  is located towards the tip.  If I am not mistaken,  2 lb.  is an awful lot.

There must be some kind of efficiency sweet spot where how strong you can build the limb versus how heavy it has to be to be that strong, yields an optimally powerful machine.   For example, in the photo below I am considering if the weight penalty incurred by including a few enhancements to increase strength and stiffness,  will be worth it in that they will allow higher draw weights. 

………Well ain’t that swank?  Hey Brutus!  look what  this here mug made.

Note to self:  No matter what the final design,  allow the final draw weight to be determined by how the tillering on the limb goes.  In other words,  keep an eye peeled for hinge points when the limbs are under load.

….Well Duh!  You know,  like in Bowmaking 101.

Whenever I think of Firefly’s modular construction and potential for easy transport, I am reminded of this scene from that Bond epic, You Only Live Twice.   Click  for vid,   20110404181228

Some of Little Nellie’s virtues have been in my thoughts lately.   God knows where I’ll be able to get enough crocodile skin trunks.

The Bard knows well the infirmity of too much thinking.    To act, and act well,  we first have to make up our minds to do so.  “The pale cast of thought” is immobilizing my desire to commit to certain final cuts on the hickory.

And so I dither,  sharpening my spokeshave but too fearful to use it.   Not  until I’m sure the tapers are reasonable.

This limb thing is becoming hopelessly melodramatic.

The limb irons still need the reinforcing biscuits to be added and then they will hardened and tempered to 50 RC,  about the same as a car spring.

This time I plan on making the limbs out of hickory.  While ash would be more authentic and marginally lighter in weight, it is not so easy to find a piece of tight grained ash that would be trustworthy enough for our purposes.  Hickory has a reputation for high strength in shock load applications.  The following chart  makes the point.

Chart copied from the Kingfisher Appalachian Hickory web site.  Click on chart to magnify.  The three different bars for “Appalachian Hickory” refers to the different grades.  The best is reputedly “impact grade”.

“Impact grade”?         ……Wow!  Wouldn’t that be groovy?  For now, the hickory plank I purchased from the local lumber store will have to do.   At least it’s grain is going in the right direction for stiffness.   …… This is right,  isn’t it?  Richard.

My experience with hickory suggests that it will bend a fair amount before breaking,  and if it does break it will not explode in some kind of splinter filled cataclysm terrifying to behold.  Clearly the Romans would not have had access to a New World hardwood like hickory, but seeing as they had a whole empire of practically virgin forests to provide them the specialized woods for their ballista limbs, and I only have the paltry pickings of a modern lumber store,  I figure it all evens out in the end.

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