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| Tops and Runout http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=29402 |
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| Author: | Edward Taylor [ Fri Oct 08, 2010 5:09 pm ] |
| Post subject: | Tops and Runout |
Today I was looking through some "AA" (engelmann) tops and found a few that were almost perfect in every regard, every grain line 90 degrees quartered, fine grains, cosmetically flawless, great tap (very lively, great to my ears at least) and stiff. The thing was, these tops had massive runout and it got me wondering how big of an issue it really is when every other characteristic is so good. Thoughts? I would imagine that there would be a large difference in the finished color of each side, so maybe these would make good tops for bursts, etc? |
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| Author: | Kim [ Fri Oct 08, 2010 5:28 pm ] |
| Post subject: | Re: Tops and Runout |
IMO run out is the least desirable flaw structurally speaking. It represents short grain and therefore a capacity to loose longitudinal stiffness. Not only that but I don't like the look under a finish once light refractions come in to play. Cheers Kim |
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| Author: | jsmith [ Fri Oct 08, 2010 5:39 pm ] |
| Post subject: | Re: Tops and Runout |
I don't consider a little bit of longitudinal runout a problem, in steel string tops--at least regarding the spruces or Port Orford cedar. However, my experience with WRC and redwood are limited, and as I understand, there could be some real issues (bridge popping-wise) especially with redwood. Now, regarding the different refraction factor of the two halves that have some runout, I feel that's a matter of aesthetics. It might bother some folks, and not bother others. But, someone who discards top solely on that criterion is potentially passing up some great tonewood. There's a mess of wonderful sounding instruments out there sporting 'two tone' tops. |
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| Author: | Andy Birko [ Fri Oct 08, 2010 7:12 pm ] |
| Post subject: | Re: Tops and Runout |
Edward Taylor wrote: had massive runout and it got me wondering how big of an issue it really is when every other characteristic is so good. Thoughts? How did you know there was runout? Chatoyance? |
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| Author: | Tom West [ Fri Oct 08, 2010 7:16 pm ] |
| Post subject: | Re: Tops and Runout |
I have to confess I'm one of the folks who does not like runout. For structural reasons,and I'm not even sure of the extent of down grade,also for visual reasons I distain it.Hard to get rid of completely and the odd time I,ve noticed a bit somewhere along the joint. If it's obvious after I join and smooth the top I don't use it. Sometimes it's awful to have such biases. Tom |
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| Author: | Edward Taylor [ Fri Oct 08, 2010 7:28 pm ] |
| Post subject: | Re: Tops and Runout |
Andy Birko wrote: Edward Taylor wrote: had massive runout and it got me wondering how big of an issue it really is when every other characteristic is so good. Thoughts? How did you know there was runout? Chatoyance? If that means a difference in color, then yes. Also one surface of the bookmatch would be smooth and the other very fibrous. |
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| Author: | Alan Carruth [ Fri Oct 08, 2010 8:47 pm ] |
| Post subject: | Re: Tops and Runout |
As has been said, runout reduces the long-grain stiffness of the wood, so, in theory, you need to leave it a bit thicker to make up for that. I have to think it might cause more porblems with cold creep as well. To my mind, the biggest problem with runout is what happens when the bridge pulls up. As the back edge lifts the runout on one side allows it to peel loose more easily, while on the other side any top fibers that stick to the bridge dive down into the top, and sometimes take out a pretty big chunk. In addition to that, runout makes it much harder to get good Chladni patterns, or clear tap tones, on the top, if you use that sort of thing. The stiffness characteristics of the two halves of the top are enough different that you end up having to carve the braces asymmetrically to get the top to vibrate right. Of course, there's runout and runout. Runout happens because the tree grew with a twist, and the twist can increase or decrease, or even change direction, as the tree grows. The 'stripe' figure you see on mahogany and other tropical woods is caused by periodic changes in the direction of the twist. Spruce trees can do the same thing, although I've never seen it that pronounced or change direction more than once or twice. Those can be the best tops, though, if the runout is not too great. Often the treee will start to grow straight, and then develop more twist as it gets bigger. In that case a 'heart match' will minimize the visual impact, and strength problems as well. You still get the light reflected in a diagonal stripe, but at least it's not two stipes that don't meet in the middle. |
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