With at cyloid, the point where it switches from convex on the top to concave on the edges is mathematically given. It is 1/2 the width, plus on half of the arching height. For a c bout that might be 50/2=25, plus half the arch height so 16-3(edge thickness)/2=6 1/2. So, the point of inflection is 31.5 mm from the centerline. 38% is concave! Much more than you would expect. In the bouts it is even a higher percentage because the arch height is lower, and the width is wider. The one constant is that the inflection point is always one half of the arch height.
If you have a cross arch from a poster, it is a simple matter to draw the inside arch in. Then draw a line for the bottom of the plate, and hold the poster upside down, and use your chain to see where the width comes on the bottom. If you do this for all the arches given, you have a good idea of where the original catenary cross arches can go to, if you want to end up with a similar arch. If you have done this for a few, you can come up with your own discoveries.
Here are a couple of sketches that show some of my ideas on cross arches. It is easier to draw them, then to put it in words.
What do you think?
Do you make the inside plate thickness adjustments the first time around- as soon as you hang the chain, or just make everything the same for starters thickness wise?
ReplyDeleteBark side down gets the nod but the other way could maybe possibly lead to a real soft weak sounding instrument. I may try that one day because playing on what I use these days gets real loud most times. I, personally, wouldn't go to thin at the lower treble bout. If you can get that area just right, the higher e strings notes will be there when a player needs them. It'll depend on grain line per inch count mostly in that area. Going thinner may be o.k., I just thin thinking about past experiences and something makes me stop in that area.
I can't comment negatively about crossing the inflection/cross arch areas. But you haven't made me a 100% believer either. Post about this on Maestronet, take the criticism or praise, if any. It can only make you better.
I do a rough, and a finish. I finish the inside arch to the drill point, and do the cross arches to the line I drew out. I get them so there are no bumps or dips, but I don't smooth them out with a sraper, and get them perfect. The size and depth are pretty much there, but not refined to a finish. Then I cut the outside, thicknessing it at around 4.5 mm for violins, and 6 mm for the cello. Then I can tap them, and see if the back and belly are around the same note. If not, I'll try to adjust the higher one lower, and try to keep the lower one as high as I can. Then I smooth the inside up, and get it just right. The edges aren't real important, because they will be cut later, after the recurve is put in. Then on to the outside. I get the long arch smooth, and to a thickness that might be just a little thick. I use a radius. I make up a gage, and try to make it as close as I can. The bouts are then thicknessed the same as the center area, unless the model is like the Montagnana where the central area is thicker. I only do that somewhat less that half way out to the edges, and then blend it down to the edge platform that is about 4.5 thick.
ReplyDeleteAre you going to set up the violins in the white before finishing? I realize that could be some time away. I see so many violins in pictures and diagrams showing different recurve/purfling trench forms that I can really tell whose way is the best. I just don't want to leave to much or to little wood when it's shaping time. Plus, I want the best results for my build{s}. I think you're on to something with the cycloid system. A lot of people don't mention they use them for design or making. It just seems easier writing down thicknesses from other plates and making it work. Between your inflection/recurve diagrams and what Saconni has written long ago, posted by others, I will figure something that will work in that area for me.
ReplyDeleteYes, I think that stringing them up would probably be the best thing to do. I thought of playing it, and seeing how the response is on each string, and working on that, and finding notes that need help, and working on that. I don't know how yet; but that is my next plan of action.
ReplyDeleteI found an article in regards to your bass bar part of the diagram with you thinking the top will drive more. It said to make the plate thickness at the end of the bass bar the same thickness as the purfling trench area, I guess. They called it the periphery channel but doesn't say how far in from the outer edge to measure thickness. Using their way enables the bass bar work better during low register string usage. I'll give it a shot on one of my plates along with the article saying to find and move the acoustical center. It's old school more than likely and I've never read about it anywheres else so I'll give it a shot.
ReplyDeleteI think that if you tune the plates with a soundpost in place, the plate will be acoustically tuned with the soundpost as the center. At least the soundpost position should work well.
ReplyDeleteThat sounds good.
ReplyDeleteI need an opinion Ken- If I use a pre-made contour pattern for the outside of a plate and then cut, carve, sand etc. to finish and then apply the same pattern to the inside and do the same wood removal procedure I wouldn't have an inflection area to deal with, right? If there's no inflection area to deal with is it a judgement called when finishing the recurve. What's funny is the words inflection and recurve really aren't defined towards the violin using the wiki pages.
ReplyDeleteI've been beat up a bit on maestronet by saying that the point the arch gois from concave to convex is at the 1/2 height point. They say that isn't the case, but they don't say where it is. If it is at the 1/2 point, the change between concave, and convex is imperceptable. If you see a sharp switch from concave to convex, something is wrong. Everything is very subtle. Inflection really just means where it changes from concave to convex, and there has to be a place like that on every plate. I suggest that it is further up that usually thought, and can almost be perceived as being flat for wuite a ways before the concavity is noticed. As far as the inside goes, the concave is done when I carve it out, and the convex blends the area to the edge. It is best to do that after the outside, or you will lose height on the arch, by not puttin enough convex on the inside, and bringing the outside arch to the inside one.
ReplyDeleteYeah, I noticed but what if it turns out your right and they're wrong? Or have you made a conclusion whose right or wrong since yesterday? If you really need the low down about it get a hold of Mr. Krutz's son Anton at K.C. Strings in Kansas City. He had some stuff posted about what you guys were going back and forth about. I can't find it anymore. Every post they shown up to comment I've never read anyone contradicting their word after they have posted. I sure they were following along yesterday, too. I believe Mr. Darnton really cares but one should at least try it his way once he's confronted with what he says. Truth be known, I tried his golden ration formula for f-hole placement. I didn't match up with what I have at home. Wasn't even close but I do think it matches the violin presented yesterday that you mentioned the area was wrong concerning a cycloid? curve around the f-hole. That one is higher up, maybe even up over and past the upper f-hole lobe. What I think you were looking at was an excerpt for Heron-Allens book concerning "wing shaping", just my opinion though This will make you feel better here it is- after I'm close to inside plate finishing I bet there's quite a few areas on my work that have inflection issues.
ReplyDeleteSomething else- I did use the ratio pattern for f-hole placement that Mr. Darnton has on his website for the plates I made. It seemed the best way to go for me with a few adjustments if I remember right.
ReplyDeleteI will wait patiently for Don Noon's future experiments to see where the best sound and power results come from while building or adjusting a violin. If the results lead to the sounds of Al Reza's first violin presented recently that would be the place to stop testing.
I'm pretty sure that I got my idea to use the catenaries on the inside, and only do the outside arch out to a little less than half way from a site written by someone who was a studen of Anton Krutz. He didn't use the catenaries on the inside, but did finisht the inside 40% and blend it out to the platform. My idea is just a hybrid of it. I have no idea what that site was. It was very good though.
ReplyDelete