Don Noon

I either missed this presentation or forgot about it, but it is quite a study. I think the general concepts and results apply to viola as well, but the exact numbers (length, height, weight, stiffness) would have to be arrived at by experience, as the viola is a different animal and you don't want it to sound like a violin. As to Manfio's original question about density, if you had a bass bar shape that was known to work with a known specific gravity, and then wanted to use wood with a different specific gravity, I would keep the original height profile and adjust the width such that w x SG is kept the same. To first order, that would keep the weight and stiffness the same. That's what I did on a violin where the bass bar SG was .48. It was a fairly skinny bar, but worked fine.

+/-0 .5 mm from a target thickness is pretty crude. I think +/- 0.1 is a reasonable target, but no need to stress over small spots that vary another tenth or so. Even with the larger variations, it is hard to say for sure whether the sound would be better or worse, since sound quality is not an objective thing. As Davide says, focus the effort on the areas that need precision. Arching and graduation likely do not benefit so much from all-out precision. Not just for sound, but for solid durability of the instrument and ease of playing. Not to great if it sounds good but is hard to play or falls apart.

Glued, yeah. The grain spacing and direction of the top and bar are different, in addition to the clean joint as Tim said. That looks like a mighty big gap between the endblock and the top plate.

For a good CNC milling machine fabricating aluminum, yes, .01 mm accuracy is reasonable. A CNC router and wood, I doubt it. Even humdity variations can change thickness by far more than that. Anyway, dimensional precision in plate thicknessing isn't going to make the end result more "perfect" (whatever that is), and thickness uniformity probably makes the result less "perfect".

$500 seems a bit high to me...

Does that include replacing the slab-cut top that some hack put on it? IMO: firewood. Nice back wood, though.

Yup. There is a wide variation in bass bar sizes and shapes that seem to work OK. I have tried the "cut it down to see what it does" experment several times, and the main things are mass and stiffness. The mass of the bar that works best is likely related to the mass of the top (inversely), and the preference of the player. I have even glued small hunks of lead to a bass bar with positive effect on a bar that was apparently too light. The stiffness that matters most is across the island and past the eyes a few cm. Not that other things don't matter, but these I have found to make the most difference.

The bass bar is one acoustic item where you can actually adjust stiffness and weight independent of the wood SG and speed of sound... if you want to. Dense wood => make it narrower. High speed of sound => make it lower. However, in my testing, it is the MASS of the bass bar that seems to make the most difference. So I finish the bass bar completely before gluing it in (taptones don't matter to me). I use high SG wood for the bar with the idea that it's more stable, and more resistant to tangential grain crushing under the bridge foot. Just an idea, no analysis or testing done. Also, I don't want to use high SG wood for tops, so this is a way to avoid throwing it out.

It's pretty much colorless, so you'd need to either use it as a clear final finish, or somehow add colorant to it. I haven't used or tested it, but it's pretty widely used for gunstocks, and there may be a good reason for that.

Similar to what I do, but my fixture is clamped to the fingerboard, rather than glued. https://maestronet.com/forum/index.php?/topic/331906-fb-location-pins/page/2/#findComment-670042

Except... it wasn't.

I tried to measure the change in properties of a wedge or two, for just a few years, and couldn't find anything obvious. One problem was that I don't have a controlled humidity envioronment, and humidity makes a measurable difference. I think that the majority of any acoustic changes happen after carving and assembly (excluding torrefying). On the issue of initial wood quality, I'm with you. Here is a plot of density vs. speed of sound for the bulk of my wood inventory (before torrefying). The Euro wood is from a variety of sources, obtained a set or two at a time. The same-log Engelmann groups show the tighter grouping of properties when you use a single log. These are sets I got from Kevin Prestwich, selected by me from several sample wedges, for the property ranges I wanted.

My pet peeve is batteries (or other thiings) with spring loading in thin plastic housings. I can't remember how many of them have had their housings crack of break due to creep, alhough a few weeks ago I definitely recall having to replace a Foredom foot switch that self-destructed that way. PVA is a plastic. Epoxy is a plastic too, but I'm not sure how it compares to PVA.

Hide glue doesn't creep under load; PVA does. Decades ago I found that out when a PVA neck re-glue self-reversed, slowly. Maybe there are some modern versions that are better, and epoxy, but that's for someone else to experiment with. The "tension" is actually compression on the shoulder; the larger heel portion is in tension. My guess is that it would work just with a strong hide glue, but if you can get a dowel in the treble side shoulder, that would be safer. My guess is also that the break didn't come from string tension, but from a traumatic whack from some other direction.

For a cheap 3/4, I'd be tempted to just glue it with strong hide glue. That's all I did with the pegbox oopsie shown here, before and after, although I had to do some clamping of the thinner areas.