After further refinement based on input from several Tradgangers from Bear State Bow Hunters in So. Cal. Here is my final spine tester design.
There are four interchangable scales that allow measurements from 20 to 200 pounds spine. Here is a detail of the "Standard Scale" measuring a GT3555 Traditional.
Now the same arrow on the "Hybrid Scale". This scale has ATA (AMO) spine on the inside and the deflection as measured by the aluminum and carbon manufacturers on the outside. Notice that the arrow spines at 525. I have others from the same dozen that spine at 500. This scale allows reading in both measuring systems at the same time.
To measure light or heavy arrows a different weight is not required. By changing the point that the arrow deflects the needle, and changing scales, these shafts can be spined. The photo below shows the different pivot locations; move it left for light spine and right for heavy spine.
This last photo shows the machine set for heavy arrows measuring a GT7595, which happens to spine at 110 pounds.
Whaddaya think?
Kevin