There has been quite a lot of discussion around bamboo and cane arrow shafts, their spine ratings, weight, diameter etc.
Having done a little work looking at the shafts I have and being personally been interested in the results I thought I would post them here.
First I must stress that the measurements and data I have are based on Tonkin. It is possible that other bamboo and cane species will show different results.
Can Tonkin bamboo shafts be sorted by weight only to give useful spine sorting?
The simple answer is no. There is a relationship between spine rating and weight, but it is not a consistent one. Generally, when averaged out heavier shafts will tend to be stiffer and weaker shafts lighter. when it comes to specific shafts of the same diameter there will however be stiffer shafts that are lighter than weaker ones etc.
The following shows the average weights of 33 inch 8 - 8.5mm shafts for the various spines. To get an idea of the weight of a 28 inch shaft you need to multiply by 0.8485
20-25# - 300 grains
25-30# - 316 grains
30-35# - 339 grains
35-40# - 356 grains
40-45# - 367 grains
45-50# - 390 grains
50-55# - 424 grains
55-60# - 433 grains
60-65# - 450 grains
65-70# - 462 grains
70-75# - 481 grains
75-80# - 498 grains
80-85# - 512 grains
85-90# - 527 grains
90-95# - 535 grains
95-100# - 543 grains
100-105# - 561 grains
While this averaged out data does show a fairly good and direct relationship between spine and weight I must stress that in individual shafts there can be significant variation.
The next thing that I thought may be of interest is the relation between shaft diameter and spine. By shaft diameter I mean the diameter at the base when cut or the thicker end of the shaft. This only became apparent to me when I had my little table and put it into a bar chart form.
Can Tonkin shafts be sorted by diameter only to give useful spine sorting?
Again, the answer is no. I hope that the following image is clear enough to show why
You will see that for each diameter of shaft there is quite a nice little peak shape but also quite considerable overlap. The 8-8.5mm shafts are a good example. The highest peak is 50-55#, but there are many more shafts that aren't. Really, the only way to get Tonkin bamboo shafts of the spine rating you want is to cut shaft diameters in the right ball ground and then spine rate them one by one.
Well, that's about all the reliable information I have at the moment. I hope it is of interest.
