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I haaaate ripples along the grain in cello ribs. The ribs I bent are supposedly all from the same chunk of tree, so I don't understand why some of them got the strong wrinkle and some not at all. Makes me want to blame the wood rather than my technique. So I guess my question has two parts: 1. Looking at unbent ribs, are there any signs that can tell if one's going to be a ripple-prone rib? Is it variation in grain? Did I thickness unevenly? Does it have something to do with seasoning? 2. Does anyone have some technique tips to share on minimizing the ripple? Photo comparing the two C-bouts below.... one has a nasty wrinkle and one does not, though they are from the same piece of wood. (This is my first cello.)
A lot has been going on since I've been away. Spent several hours the other night watching Davide Sora's violin making videos on YouTube the other night. Wonderful stuff! Great way to learn refinements in techniques I had only guessed at in the past! One of the first video's I watched was the one on tapering the ribs. (Thanks for the translations of the text!) On the instruments I have built so far I have done the dummy approach of a gradual taper from end block to neck block, not understanding the principle of tapering from the upper blocks to the neck block. So my instruments have no stress placed on the front of back plates. Most observations on instruments with this taper taper is that it is exclusive to the front plate, while back plate remains flat. In Davide's video he distributes the 2 mm taper on the violin to 0.5 mm on the back plate and 1.5 mm on the front plate. I'm interested in applying a "proper" taper going forward and am interested in the reasoning behind the taper. And also the reason for making the decision to taper both plates. I mean, it makes sense if the reasoning behind the taper has to do with a desired change the resonant response of each plates. Certainly such a stress would alter the way the plate vibrates shifting or perhaps deadening the some key body resonances. Perhaps this is a way to mute some troublesome resonances that lead to wolf tones? It must alter the tonal characteristics in a positive way otherwise this refinement would not have been made. Interested to hear your feedback on this.
Here is the custom design I created to thin my violin rib. It is basically a suction MDF box with a groove over it that holds in place the rib. It works over the table of a press drill. I was using a Delta press drill with an extra large platform. I was using a Safe-T-Planer mounted on the drill to thin my ribs. It is very accurate. It does not produce a fine powder like when we are using a belt sander. It is a known that the fine powder coming from hard wood is toxic for the lungs. It is pretty safe to use the Safe-T-Planer. It can be found here: http://www.stewmac.com/Luthier_Tools/Types_of_Tools/Planes/StewMac_Safe-T-Planer.html?utm_source=bing&utm_medium=cpc&utm_campaign=TXT%3A New Products&utm_term=safe t planer&utm_content=Safe-T-Planer The measurements of the box are:Length = 762 mmWidth = 153 mmHeight = 120 mmThe MDF thickness is 16 mm.The width of the groove is 43 mm. I used a router to make that groove being .6 mm deep.The open part for the adaptor suction part is 56 mm wide. I connect to it a Shop-O-Vac vacuum. We start to thin from the middle of the rib in place, then going to one extremity, and we start again into the centre and we complete until finished toward the other extremity. This approach about 80 % of the time usually used with the traditional method using a plane.