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Jim_B
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Look's like the folks who make those quality 'Stentors' have been found out. Just got my January Strads for sale and the particle scanner shows a very clear picture of a portion of a Stentor violin top and bass bar with the bass bar grain orientation completely wrong! A quick scanning of the article and one might think that a Guadagnini had been built that way but closer examination reveals the first photo to be a Stentor and the Guad example is correctly shown a couple of pages later.

Nevertheless, interesting stuff.

J. Brown

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It is interesting how much detail that the scans show, and how clear the images are. On the Guad large internal patches show very distinctly, but have been fitted extremely skilfully.

For the job expected of a basic Stentor student violin it's just not going to matter which way the bar is cut, there are certainly far worse violins out there to learn on.

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... the bass bar grain orientation completely wrong!

Yes, I noticed the slab-oriented bass bar, and had seen this somewhere else before, so I knew it was a cheapo.

However, I see it only as "non-traditional", and not necessarily "wrong", strictly considering function. The traditional way is easier to cut, but I know of no technical reason for there to be any acoustic or stability benefits over the slab orientation. There may even be a very slight stability advantage for the slab bar, but I haven't tested it yet.

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obviously spruce is stronger along the grain, 1/4 sawn than it is across the grain, slab cut, so i think it fairly obvious that a 1/4sawn bass bar would be stronger at supporting the arch and resisting down pressure than a slab cut bar, but here on maestronet anythings possible

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i see your point, i wasnt argueing with you jacob, but 97%+ of violin makers seem to agree on 1/4 sawn, i thought the purpose of the bass bar was to strengthen the arching and resist down pressure from the bridge, not exactly a call for more flexibility

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I have seen "Slab cut" Bass bars on old French instruments. Not fitted, but bent in. Seemed to work.

OK I'm a bit confused ....If the growth rings of the bar sit in the same orientation as the top, ...quartered ...is that ideal? In my mind the bar would be slab cut, please, have I been doing the bar wrong???????? Or is slab cut different when we are talking bass bars? signed, confused

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OK I'm a bit confused ....If the growth rings of the bar sit in the same orientation as the top, ...quartered ...is that ideal? In my mind the bar would be slab cut, please, have I been doing the bar wrong???????? Or is slab cut different when we are talking bass bars? signed, confused

For the sake of a discussion where we all know what each other are talking about, I meant that a quatered bar is what we all know, and a slab cut at 90° to that, ie. with the annual rings at 90° to the belly rings.

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obviously spruce is stronger along the grain, 1/4 sawn than it is across the grain, slab cut, so i think it fairly obvious that a 1/4sawn bass bar would be stronger at supporting the arch and resisting down pressure than a slab cut bar, but here on maestronet anythings possible

Sometimes things are not obvious, and this is one of those times.

In the microscopic view (taken from this paper by Jim Woodhouse), you can see the annular rings (well, one of them), and the fact that the cell walls are lined up quite well perpendicular to the annular ring, but more haphazardly in the direction of the ring.

post-25192-0-04770700-1326245242_thumb.jpg

This is the reason that the modulus in the direction of the ring (tangential) is the LOWEST, and most prone to cracking across this direction.

Here's another indication that the rings are not "little, strong beams"... where are all the cracks? Through the rings.

post-25192-0-92465500-1326245257_thumb.jpg

In spite of all of this, I don't think it matters much. As a test I cut a precise square cross-section spruce stick. The tap tone was identical no matter which way I checked, so the real-world bending stiffness was the same. For long-term stability, it might also not matter much. But, in theory, the "slab cut" bar should be better. I just haven't gotten around to doing a test yet.

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youre science aint rocket science, don, strength and tendency to crack are two independent factors, if you take your perfectly 1/4 sawn cube of spruce, quite a long piece then put a weight on the end, while you clamp the other end, you should see that the 1/4sawn orientation gives less deflection, showing greater strength, than when testing across the grain, which should be weaker or more flexible as jacob said, this aint rocket science its the most basic properties of softwoods, oweing to the winter growth being stronger than the summer growth

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The traditional way is easier to cut, but I know of no technical reason,,,,,,,,

Very late one night, after a long long day, I picked out some spruce from the pile that looked about sized for bass bars.

It took me an hour to figure out the piece was slab cut. And only after I planed it to thickness, cut to length, and rough fit it. Once I got into the fine fitting things just seemed impossible to get working right.

It finally dawned that My knife work,scraping, file work was creating a wash board surface. The wash board coming from the soft growth/hard growth differences. Doh!

A good lesson to learn, though. Slab cut is harder to fit accurately, and so (for me) not worth worrying about.

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oops indeed; well a thorough google search has partially convinced me that i was wrong about slab cut spruce being weaker, someone had done the test i reccomended and got virtually identical deflection on spruce square rods, whether they were oriented 1/4 or slab, i did see a lot on guitar forums about 1/4 vs slab having different tonal properties, but strength didnt seem to be the issue, my apologies.

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Sometimes it's hard to keep straight which direction they're talking about stiffness. It always helps (for me, anyway) to think in terms of the tree: radial... perpendicular to the rings... is much stiffer than tangential...along the direction of the rings. This of course is ignoring along-the-grain, which is way stiffer/stronger than the radial or tangential.

For a top, which is thin and wide, the concern is crossgrain stiffness and split resistance, so quartersawn will be best. For a bassbar, who really cares about "crossgrain", i.e. across the 5.5mm width of the bar? The concern should be vertical stiffness and split resistance, where flatsawn might have a tiny advantage.

But, the annoyance of cutting shallow angles across ring lines is an immediate and real problem, and a good fit could easily trump the other issues.

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Sometimes it's hard to keep straight which direction they're talking about stiffness. It always helps (for me, anyway) to think in terms of the tree: radial... perpendicular to the rings... is much stiffer than tangential...along the direction of the rings. This of course is ignoring along-the-grain, which is way stiffer/stronger than the radial or tangential.

For a top, which is thin and wide, the concern is crossgrain stiffness and split resistance, so quartersawn will be best. For a bassbar, who really cares about "crossgrain", i.e. across the 5.5mm width of the bar? The concern should be vertical stiffness and split resistance, where flatsawn might have a tiny advantage.

But, the annoyance of cutting shallow angles across ring lines is an immediate and real problem, and a good fit could easily trump the other issues.

For me it has always been that quarter cut spruce and maple are more resistant to splitting along the longitudinal axis of the violin. The worst cases of splitting I have seen have been in slab cut backs and tops.

Bruce

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This is the reason that the modulus in the direction of the ring (tangential) is the LOWEST, and most prone to cracking across this direction.

Here's another indication that the rings are not "little, strong beams"... where are all the cracks? Through the rings.

post-25192-0-92465500-1326245257_thumb.jpg

The crack direction should reflect the direction where the dimensional changes are largest when the wood dries. Swelling and shrinking due to moisture variation is the largest in the tangential direction.

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Anders,

I know that you know this stuff... re-read your last couple of posts.

Tangential = along the ring direction = weakest = most shrinkage = most cracking (through it) = least stiff.

The cracks in the log photo go in the radial direction, but the crack are through the tangential (weak) direction.

I have been checking dimensional changes in my wood processing, and the thickness of my quartersawn wood (i.e. tangential) shows the most shrinkage, and also the most change with moisture content variations. This is all consistent.

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Anders,

I know that you know this stuff... re-read your last couple of posts.

Tangential = along the ring direction = weakest = most shrinkage = most cracking (through it) = least stiff.

The cracks in the log photo go in the radial direction, but the crack are through the tangential (weak) direction.

I have been checking dimensional changes in my wood processing, and the thickness of my quartersawn wood (i.e. tangential) shows the most shrinkage, and also the most change with moisture content variations. This is all consistent.

Yes, thanks Don. I mixed the tangential and the radial direction. I think I was thinking correctly but wrote it wrong.

The cracks go in the radial direction, but they are caused by shrinkage of the wood in the tangential direction. Then both the wood is weaker and shrink more in that tangential direction.

Does the modulus of rupture and the moduluses of elasticity follow each other directly? That is: can we predict one of them from the other?

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I knew this would get you guys going. :lol: That's another hour away from building. For some of you more! As for me, I believe the traditional grain direction makes the bar much easier to fit and shape. Aside from that, the main reason I brought it up is that I don't see why they chose to introduce a Stentor in an article which features a Guadagnini. Looks like they have a perfectly clear view in the Guad pics.

JB

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