Spine question

[Mafort]

Soo say I have a few split timber shafts that is like to make into compound shafts. Would this change the spine of them? I’m only hollowing the first 3 inches or so maybe less. If it does weaken then how high or low should I spine them to work with a bow?

[Pat B]

If it adds weight to the front end it will reduce the spine, by about 5# for every 25 grains added. Just adding a stiffer 3" to the front end shouldn't make much difference other than it's weight. Spine testers check the deflection in the center of the shaft.