A couple of years ago one of Firefly’s field frames showed us a point of potential weakness in the Orsova design. While exploring some typically enthusiastic poundages, the straight stanchion on the port field frame took a slight and localized bend just beneath the loop that captures the shorter fork on the kamarion. In the photo below, the red arrows indicate the direction of this old injury.

It was this area of potential bending that forced us to limit draw weights to under 4000 pounds. At the time I had welded in a straight section of higher grade 4140 that was intended to beef up this area. It appears that some of my welding back then was not up to par as it is now possible to see a small crack forming on the outboard side of that stanchion. Easy to fix by grinding out the affected area and rewelding. I only mention it because it does highlight that same area as a place most likely to fail in the Orsova design. If I had it to do over again the field frames would be made entirely from 4130 or 4140 rather than the mild steel we had used at the start of this project.

I am pleased to report that now the kamarion has been disassembled from the machine, it is possible to see that its deliberate prebend (in a deflexed direction, to borrow from bowyer speak) is still there. In other words, if one were to look down on Firefly from an overhead position, the center of the kamarion should appear convex relative to the back of the machine. It is good to see that the kamarion has not taken a backward (reflexed) set when repeatedly stressed by a couple of hundred firing cycles. The kamarion is basically one big spring, and if it fails by having its center bend backwards too far at maximum draw, then the forks on the kamarion twist inwards towards the centerline of the machine. This in turn removes some of the support that prevents the top of the field frame from twisting inwards and down under the torsional loads. Not a good thing if one is playing with those higher draw weights.

The straight edge in the photo below gives some indication of this desirable, forward facing deflex in the kamarion. In short, the deflex acts to stiffen the kamarion, which in turn, protects that potential weakspot on the top of the straight stanchion. So glad it is still there.

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