Hi again Rainer,
After working through the weights of various parts which you supplied I decided I couldn't get your numbers to add up properly. I decided to disassemble and weigh my own Blue Olive badge 5" Supra (date stamped Dec 15, 1969) and my 5" Black Beauty from 2002. Here are the results. You will see that I get within 2 grams of the total (full dress) weight based on the sum of the separate parts:
[img]http://black.net.nz/cym2017/supra-model-1.png[/img]
I can't tell what is different about your weights, but they don't add up properly in the same way. In the case of your Acro I can only account for 70% of the expected weight of the full dress drum. In the case of your 6.5" Supra the sum of the components only account for about 75%. So I presume I am missing some things, and that's after adding back in estimates for heads and hoops (based on the weights of mine). I think we need to check over the definitions carefully. One obvious difference is that I include the knob in the tone control weight. But what else might be different? I don't see any weight for the butt plate on yours but if you included that in the 12 hole strainer weight then somehow yours ends up 4g lighter than mine which seems odd. If you didn't include the butt weight with your strainer weight then did you not report it? Any chance of getting you to create a table as I have which accounts for all the components plus the total full dress weight? x-mas3
The Supra has COB hoops, and the Black Beauty has steel hoops. Steel hoops are a little heavier. The other notable difference is that the butt plate on the Black Beauty is about 70g heavier. I'm not sure exactly when the design changed for the butt plate. The Blackface 2 hole P85 is also 20g lighter than the more modern P85.
In practical use my scale is accurate to about 2g. In order to get a more accurate weight for components like tension rods, I weigh all of them together then use the average. I did the same for lugs. In all cases the washers and screws which go with a particular component (say the 2 hole strainer) are put back into the strainer before weighing.
Once I get consistency in the weights of parts and the full dress drums I will move on to using the density of the different shell materials to double check on the bare shell weight. In the meantime I have confirmed the approximate 1.7mm thickness of the shell on my Alu Supra, but not with my more accurate micrometer (which is, alas, dead and needs replacing). It also seems like the modern brass shells are 1.2mm, so thinner than the Alu shells.
I've also got another set of steel and COB rims which I'll add into my comparisons.