The Mk VIII limb irons have been heat treated to 40 RC using a double temper technique.  The basic procedure is as follows:  the irons were placed in the forge and heated to 1600 F and soaked at that temperature for 1/2 hour.  Upon being removed from the forge they were immediately quenched in my stinky old vat of used fryer oil.  After enduring ten minutes or so of olfactory  grumbles from the Rebecca,  the now room temperature irons were put back in an 800 F forge and carefully monitored to maintain that temperature for 1 hour.   This is the procedure known as tempering.  The next day this tempering procedure  was repeated and that it is why it is known as “double tempered”.  The idea here is to remove any last traces of brittleness.  These new irons  should have a tensile strength of 186,000 lbs per square inch, and at 40 Rockwell they should have mechanical properties similar to a soft spring.  That is to say, they have high strength but are still  somewhat ductile.

And so we are now ready to fit up some new Ash limbs to these souped-up irons.  There is a definite “been there done that” quality to this stage of Firefly’ s development.    The CG’s willing,  groundhog day is almost over.

3 Responses to “The double tempered groundhog.”

  1. Captn harpoon says:

    Hi Nick.

    Im missing some Firefly data…how long is the string with the arms in the new position with the brass inserts removed?

    Also, what is the length from the center of spring bundle to where the string attaches?

    From my study of both the Hatra frame and the Orsova, I cannot get it out of my mind that for both machines total arm rotation did not exceed much more than 65 to 75 degrees if total rotation when used for light weight sharps.

    I know this goes against just about everybody else and their cousins opinion, but I have always swum upstream when all others go with the flow…

    In the old 12 oclock arm position we know the first 35 degrees produced approxamately one half the total draw length (30 – 33 inches)with Firefly getting approx. 50 inches of draw from about 70-75 degrees?

    So….in the new arm postition, the first 50 degrees of rotation produces how much draw as a percentage of total available draw of approx. 60 inches?

    I am thinking (theorizing) that the new arm position will act much like a compounding design, again lowering the total amount of rotation needed to accomplish 400fps plus given that higher performance can be attained simply by increasing the string tension in the rest position.

    The higher performance capability of the inswinging design has always been assumed to be because of the extended arm rotation capability up to a theorized 120 degrees max.

    While there is a few different setups you can use to “tune” the machine, only one will produce the highest bolt speeds.

    While I have no doubt that 400fps will be accomplished this round of testing (barring material failures), I am left wondering if it can be accomplished using only 65 degrees of rotation, the same as an outswinger.

    Again it is only my opinion that to prove the inswingers design ballista. it must use only the same amount of rotation as the outswinger ie – an inswinger

    At 425 fps, Firefly will match the performance of the worlds most advanced modern crossbow – the Scorpyd slp 165.

    I am real stoked to be able to watch the new build testing, and looking forward to the videos. If you are able to hit 450fps, then a 3500 – 4000 foot range may be possible.

    Not sure but I think Firefly could make it into the Guiness book of records.

    Good luck and looking forward to the upcoming blog entries.


  2. Nick says:


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