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Michael Darnton
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 Posted: Sat Mar 09, 2013 7:08 pm Post subject: |
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The next time any of you graduate a back, I want you to notice something. First wood has a twist. For instance on most tops and backs there is a direction, usually counterclockwise, that's easier to work in.
Second you're probably right handed.
Think about how that affects the various areas as you graduate, and what the results would be if you didn't use a caliper, and didn't care too much about grads.
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jacobyfineviolins
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| Posted: Sat Mar 09, 2013 7:25 pm Post subject: |
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L P Reedy, thank you. I see some of that, as well. I have tried on the last twenty or so violins to have areas which seem to bear thinning as my go-to spots for flexibility adjustment, or weight reduction.
The bass side upper bout above the corner, and anywhere where the recurve from the arch follows into the channel.
These seem to repeatedly be thinner on Cremonese instruments, so my assumption has been that I should go to these areas when I need to adjust my plate.
Michael, I love your Occam's Razor approach to method. I will be buried in a back plate tomorrow and Monday, and I will try and keep your prompt in mind.
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kjb
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| Posted: Sun Mar 10, 2013 9:21 am Post subject: |
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| Michael Darnton wrote: | The next time any of you graduate a back, I want you to notice something. First wood has a twist. For instance on most tops and backs there is a direction, usually counterclockwise, that's easier to work in.
Second you're probably right handed.
Think about how that affects the various areas as you graduate, and what the results would be if you didn't use a caliper, and didn't care too much about grads. |
if I am following what you are saying , I see this when I have been doing the arching, the wood cuts easier in one direction and i end up taking off too much because it is moving so well. |
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Michael Darnton
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| Posted: Sun Mar 10, 2013 9:27 am Post subject: |
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Right. And it you weren't using calipers, only a crude system for marking, and you didn't really care, you can work around the violin and see what the general tendency to wander from the target would be in each area.
In the current discussion, for instance, I have always found it easier to do where the label goes than the precise opposite spot, because on the label side I am planing out towards the lower bout, but on the other side the twist of the wood encourages me to work planing into the c-bout more.
Keep your eyes open, and you'll see the wood always twists the same way. . . at least in the Northern Hermisphere. :-)
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jacobyfineviolins
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| Posted: Mon Mar 11, 2013 1:38 pm Post subject: |
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I wonder, Michael, (and let me know if I flogging an exhausted horse here) if you advocate a don't-really-care graduation plan, relying on your arch shapes and flex and feel, or if you're just interested in the coincidence of the graduation maps' corollary to ease of carving direction and right-handedness?
My sixth grade English teacher would have my ears.
Is it an interesting observation only, or a gateway to method?
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Michael Darnton
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| Posted: Mon Mar 11, 2013 1:43 pm Post subject: |
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I just let it all happen. If I'm making a Strad model top, for instance, I use my graduation punch at 2.7mm and never measure or check again. If I'm making a del Gesu top, I set it to 3.5mm.
I never twist, flex or tap, or measure with a real caliper.
Talking of flex; how can one even attempt to resolve the importance of flex if del Gesus are 50% thicker than Strads and work equally well, if differently?
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jacobyfineviolins
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actonern
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| Posted: Mon Mar 11, 2013 3:26 pm Post subject: |
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And Gadzooks.
Now I'm going to root through the posters to see if one piece backs don't have that same effect!  |
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R Mac
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| Posted: Mon Mar 11, 2013 4:20 pm Post subject: |
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| Michael Darnton wrote: |
Keep your eyes open, and you'll see the wood always twists the same way. . . at least in the Northern Hermisphere. |
Let me see If I am following this. If I understand the conventional wisdom; a tree will tend to twist as it grows in response to the prevailing wind if one side of the tree is more exposed and the other side is more sheltered. So, it we postulate a tree growing on a northern slope in North America, the prevailing west (ish) wind will act upon the northern branches of the tree and the southern branches will be somewhat sheltered by the slope. If that's right, then our typical North American, shade-grown tree should exhibit a slight "left hand" twist, if we recon it like a screw thread.
I think that's consistent with what you said you have found, but I am having a bit of difficulty thinking it through once the wood begins to be a fiddle plate.
My analysis is, of course, predicated on the idea that shade-grown vs. sun-grown is an important consideration when when deciding which trees to fell and process as tone wood.
If that's not the case, then perhaps the twist is not wind induced at all, but somehow a result the growth of the tree responding to the apparent diurnal path of the sun. It that is the case, then southern trees (in the Northern Hemisphere) should (on average) exhibit less twist than northern ones.. Conversely, Southern Hemisphere trees should twist the other way in direct proportion to their latitude.
Mac |
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ctviolin
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| Posted: Mon Mar 11, 2013 9:18 pm Post subject: |
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| R Mac wrote: | | Michael Darnton wrote: |
Keep your eyes open, and you'll see the wood always twists the same way. . . at least in the Northern Hermisphere. |
Let me see If I am following this. If I understand the conventional wisdom; a tree will tend to twist as it grows in response to the prevailing wind if one side of the tree is more exposed and the other side is more sheltered.
If that's not the case, then perhaps the twist is not wind induced at all, but somehow a result the growth of the tree responding to the apparent diurnal path of the sun. It that is the case, then southern trees (in the Northern Hemisphere) should (on average) exhibit less twist than northern ones.. Conversely, Southern Hemisphere trees should twist the other way in direct proportion to their latitude.
Mac |
I believe the twist he was referring to, was because of the rotation of the earth.
This will be interesting.
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R Mac
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| Posted: Mon Mar 11, 2013 10:40 pm Post subject: |
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I spent some time trying to find out about helicaly twisted trees on the web. It sort of looks like no one really knows, or if they do, it hasn't trickled down out of the academic publications yet.
I am having trouble imagining a mechanism that involves Corioli's effect, so I would be glad to hear one.
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Michael Darnton
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| Posted: Mon Mar 11, 2013 10:49 pm Post subject: |
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Some of us have speculated about it, but we don't really know. The resin molecule of spruce and fir trees has a helical spin to it, too. There's been discussion about that, whether it differs between continents, etc. No one cares enough to find out, I guess.
The stockade at Ft. Wilkins, in Michigan:
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R Mac
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| Posted: Mon Mar 11, 2013 10:53 pm Post subject: |
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Micheal,
Let me see if I am understanding what you are doing with the plate gradation.
You get the arching to be "bang on" to a series of curtate cycloids.
You mark the plates for what you judge to be the correct thickness, all nice and symmetrical.
Then you cut down to your marks, but you don't "sweat it" if the places that are easier to cut end up a bit thinner than the ones that are harder to cut.
The result is a plate that is mathematically perfect on the outside, but just a bit wonky on the inside.
Have I got that?
Mac |
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R Mac
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| Posted: Mon Mar 11, 2013 11:01 pm Post subject: |
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| Michael Darnton wrote: | Some of us have speculated about it, but we don't really know. The resin molecule of spruce and fir trees has a helical spin to it, too. There's been discussion about that, whether it differs between continents, etc. No one cares enough to find out, I guess.
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I found a paper on the web (a forestry document if I recall) that said that Engleman spruce was very prone to the twist thing, but they did not speculate about why.
Do you find yourself rejecting wood because it is too twisty? I don't expect anything like those pickets to find their way into a tonewood suppliers stock, but you know what I mean.
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Michael Darnton
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