Davide Sora

Is it possible for them to be made with a 3D printer? the plastic used in 3D printers can be very rigid, but I'm just speculating, I don't own a 3D printer

That thickness gauge barely reaches the area around the f-holes, I don't think it was used to measure thicknesses during construction. Perhaps to check the thicknesses of the central area of finished instruments that passed by in the workshop

The biggest pitfall is considering it like a big violin, it's not. For example, the top plate of the viola must be less stiff than that of the violin, which is why the thicknesses are practically the same. If the viola ends up too "violinistic" (i.e. too bright), it will not be a good viola. Of course, that's my personal opinion. Another interesting aspect of the viola, many different opinions...

Have you tried asking Scrollavezza&Zanrè directly? Since you have been a customer of theirs (purchased the book), they may be willing to answer your questions.

I use a more modern pencil, no marks left

Hmm...it makes perfect sense to me. When you have the ribs at full height (without the taper yet), draw a line with a scribe marker with the measurement of the taper at the upper block (about 2 mm), and use it as a reference to reach when planing the taper. Well, I would have just made it shorter to let it disappear, but having it longer gives a reference for the inclination of the ribs outside the upper block. The same line is also visible on some Amati instruments.

I'm sorry, my bad, I read too quickly. I deleted my previous post.

Be prepared to wait a long time. Then, there is the problem of the alcohol which will absorb a lot of moisture.

More or less, some are more fleeting, some less so, but any color will fade a bit over time. This is why many try to get much of the color from resins, and then add pigments, they can be more stable, but it's not always the case.

Deleted

Same here. Although I used the glitter test in the past, I soon stopped. The only real use I got from it was to identify the various Modes to understand which ones to attribute the various frequencies that you hear in a plate when you tap it. This can be particularly useful in cellos, where it is easy to make a mess; for example, for some years I mistook the M3 or M4 for the M2, because they were louder and clearer than the M2 (which doesn't happen in the violin). Then doing the glitter test I discovered which was which, and I corrected my data. Luckily I didn't give too much weight to the M2, otherwise I would have made a real mess.

Thanks for the report, I replaced the links in my previous post and they should work now. I'm not familiar with Auriou rasps, but they don't look bad. The problem with rasps is that until you've tried them you can't understand how they work, especially regarding the smoothness of the cutting action and how clean a surface they create.

When I get to F# for M5 I would cut the F-holes anyway, it doesn't matter where the M2 is. Paying attention to the nodal lines doesn't make much sense to me, but it makes even less sense at such an early stage. However, if you want to find the nodal pattern of the M2, you can locate the frequency by ear and tapping, then reproduce this specific frequency with the speaker and move a few Hz up and down to sharpen the nodal lines of the Mode. If you hear it by ear, it must form.

I think that even in the current state of your top plate you should obtain the nodal figure of M2, as @Evan Smith says it is one of the easiest to form. How do you detect modes? I suspect you're doing something wrong, follow Evan's suggestions and try again. If you clearly hear the mode 2 note by ear while tapping, it means the pattern is forming, if it wasn't forming you wouldn't hear the note clearly. Then, is your top plate without or with Fs? without or with bassbar?

It seems very strange to me that the nodal pattern of your M2 does not form, usually this happens when it is very rigid (i.e. very high frequency), but the more flexible the plate becomes, the more clearly the nodal pattern forms. If your M2 is around E, that means it's more than one octave below your M5, so more flexible than if it were just one octave. Are you sure you placed the plate supports and excitation point correctly? PS It's been many years since I did any glitter test, but from what I remember, the correct positioning of the plate is essential, and the power of the excitation is too, whether it is too much or too little, you have to find the right one.