I started bareshaft tuning recently after getting erratic arrow travel as I work to increase my yardage past 50 yards. Found quickly that I’m under spined. New arrows on the way. I noticed with some arrow builders they talk about how they locate the backbone or the heavy side of the shaft and mark it. What aspects of tuning would I need this information? I’m guessing their is some importance there with that but I can’t figure out how that impacts my tuning. Anyone have some background to help me out?

you need a spine tester

The only way I know to finding the heavy side of an arrow is to float it in water. This is a static test; arrow not being shot from bow. Some people plug each end with something like cork. I just leave each end open; give each arrow a little spin when I drop it into the bath tub. The heavy side goes down; then I mark the top of each arrow. This is were I install the cock vane on each arrow. I mainly do it to clean the carbon dust off from outside and inside the shaft; to help the insert stick and and vanes stay on. The purpose is get all the arrows to flex the same way coming out of the bow when shot. I am someday going to test this theory; by paper tunning each arrow. A lot of time.
Another way to do the same test dynamicly, shooting the arrow from the bow, is to nock tune each arrow. This is done using the hooter shooter machine. This is were you shot the bow from the machine at 20 yards and spin the nock’s around untill each arrow basicaly hits the same hole. If you don’t have a hooter shooter; one would have to pay someone else to do it for you. keystone country store advertise doing this for $60.00 a dozen. By moving the nock around to different vanes you are getting the arrows to flex the same way coming out of the bow. This is the best method because the arrow is under pressure being shot from the bow. I think it does work. I do not make a living at archery and not a very good shot; but if you were this method would be needed.
Paper tuning each arrow would also do the same thing; seeing the flex of each arrow and then moveing the nock to different vane and shooting the arrow again threw paper. The problem with this method would be human error shooting the bow; getting a different paper tear with the same arrow.
You could number your arrows, keep a log of were each arrow lands while shooting. Then if one keeps going off from others; move the nock to a different vane. Keep writting it down untill all the arrow hit the same location.
I have heard people doing this on broadhead tunning arrows. They rotate the nock to different vane. They also use hot glue on the inserts. Then they reheat the broadhead and spin the insert around inside the arrow; let cool and reshot the arrow to see if it groups with the other broad head arrows.
All you are doing is matching the flex of the arrows coming out of the bow when shot; so they will all recover the same way and at the same time. I’m sure I missed something; Hope this helps. craig

If you order shafts or arrows from south shore archery they spline test them for you and mark the stiff side. They have good prices, great service, and pretty much any option of shaft, wrap, nock, incert, and fletching combo you could want. They are out of florida and Im in mn and still order all my arrow shafts from them.