ABRASIVES COMPARISON - multiple types, grits compared by 4 testers

[FenceFurniture]

Ps sorry but what timber did you use again

Non-specific Eucalyptus - an old fence post, so probably "North Coast Hardwood"

[fletty]

OK now ladies and gentlemen, I am the previously announced "talented amateur with a scientific mind (and now 9 and a half fingers!)" although if I had seen this description earlier AND read this thread, I probably would have declined! Yes, until now, I have not even read this thread!
I had previously thought that sharpening raised unnecessary passions but I now see that "abrasives" is just as bad.
Many years ago, I did a lot of abrasives testing (paper backed wet and dry for an Australian paint manufacturer) and found that by cutting accurate discs, 'sanding' clear plastic with calibrated pressure and then measuring light transmission gave a basic comparison between grits and brands BUT this did not translate into the real World as different operators used different techniques making grit and brand comparisons irrelevant. (BTW, the biggest variable there was amount of water and slurry left on the paper!)
I have therefore carried out a set of COMPARISONS of discs with the same grit on the same job and hence same timber. My results are totally QUALITATIVE as I found too many variables in (particularly) technique to allow me to do any meaningful QUANTITATIVE comparisons. As I stress in my report, I carried out these comparisons using my standard methods of work because, rather selfishly, I was doing it to be meaningful to ME!
After some consideration, I believe that the part of my standard technique for sanding that has had the greatest impact on the comparison, is that I most frequently sand workpieces narrower than the disc diameter and so there are 2 edge crossings for every rotation. This probably explains why I have had many discs tear before having the abrasive expire.
So, for better or for worse, I attach my findings......

fletty