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| Scoring acoustic bridges on reglue http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10137&t=51037 |
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| Author: | DanKirkland [ Wed Sep 26, 2018 9:13 am ] |
| Post subject: | Scoring acoustic bridges on reglue |
I'm certain this has been covered before. I'm not a fan of scoring a cross hatch pattern on the sole and top of bridges. This past month I've had a total of 4 that have "popped" from being scored and the small patches of the top that are separated gave way and came off. When I first started I did it on 2 guitars and both had come back within a year from the bridge lifting again. The same thing with the top grain being cut was the culprit. In my mind I can see how this might make sense from a certain perspective to make the glue hold better. Sort of the same thought with a toothing plane from way back. But seeing these consistently come loose has me questioning this method. From what I understand a smooth surface can get greater gluing area and can also easily be restored in the future should it need to be glued again. Any thoughts? |
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| Author: | Pmaj7 [ Wed Sep 26, 2018 9:51 am ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
It's fairly common that people used to score the underside of the bridge. Are you talking about scoring a cross-hatch pattern on the soundboard as well? If so, I've never heard of that and it sounds like a very bad idea. |
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| Author: | DanKirkland [ Wed Sep 26, 2018 10:30 am ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
pat macaluso wrote: It's fairly common that people used to score the underside of the bridge. Are you talking about scoring a cross-hatch pattern on the soundboard as well? If so, I've never heard of that and it sounds like a very bad idea. Bridge and the top yes. On each one the fibers of the top give way and the bridge starts to peel off. |
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| Author: | Chris Pile [ Wed Sep 26, 2018 12:40 pm ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
In 40 plus years of doing repair I've never scored the bottom of the bridge.... |
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| Author: | Frank Ford [ Wed Sep 26, 2018 1:39 pm ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
It's a well-documented fact that scoring does not help wood glue adhesion. Too slick a surface CAN make for poor adhesion, although it's hardly ever and issue with hand worked scraped or sanded surfaces. I recall an issue with a run of factory guitars where the person using a router to remove finish from the top glue surface was trying to "save the company money" by not changing router bits on the prescribed schedule. By using a dull bit, he actually glazed the surface of the spruce, resulting in bridge glue failure on a fair number of instruments. One argument I've heard in favor of 'toothing" the bottom of bridges has to do with positioning when it's glued. The idea is that the rougher surface may keep it from slipping as it's clamped. I've not noticed any such benefit myself. Speaking of scoring/cross-hatching - - - It doesn't get any worse than this example: Attachment: scoredtop02.jpg
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| Author: | Ruby50 [ Wed Sep 26, 2018 5:16 pm ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
There is another thread active here in the building page called"Brace radius sanding jig" and on page 2 there is a lively discussion of this. On page 3, Don Parker posted this: https://www.popularwoodworking.com/tech ... -or-rough/ One of the letters following the article states that the FAA (airplane regulators) will not approve sanded joints for gluing, only those cut with an edge tool Ed |
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| Author: | DanKirkland [ Thu Sep 27, 2018 9:15 am ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
Thanks for the comments and info Frank and Ed. I actually found out that there's a shop in my area that has been "doing it that way for years" so I have a feeling I've not seen the last of them. Oddly enough it's the same shop that SRV went to back in the day. |
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| Author: | Pmaj7 [ Mon Oct 01, 2018 8:56 pm ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
I can see the idea that scoring the bridge would help the glue to grab onto it although most people nowadays don't think that's true. Although, it probably would be a good idea if you were using epoxy. But, scoring the Spruce seems like you would be losing the strength in the wood fibers right where you want it. Sort of like when you score the Finish around the bridge footprint you would be careful not to cut the wood fibers especially in the back of the bridge where all the force is wanting to pull it up. |
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| Author: | DanKirkland [ Tue Oct 02, 2018 9:37 am ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
pat macaluso wrote: I can see the idea that scoring the bridge would help the glue to grab onto it although most people nowadays don't think that's true. Although, it probably would be a good idea if you were using epoxy. But, scoring the Spruce seems like you would be losing the strength in the wood fibers right where you want it. Sort of like when you score the Finish around the bridge footprint you would be careful not to cut the wood fibers especially in the back of the bridge where all the force is wanting to pull it up. Odd, I just had one come in on Saturday that was epoxied. Same thing happened, it just ripped the top fibers right off. The scoring did zilch to help it adhere. I had a long discussion on this with one of the older repair guys around me that I know. He seems convinced that it's the only way to do things. I just left it at agreeing to disagree on the matter. However this recent one with the epoxy makes 5 so far in less than 2 months. I am simply going to fix what I can and leave whomever is doing this to their old ways. |
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| Author: | Pmaj7 [ Tue Oct 02, 2018 9:58 am ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
I was just referring to scoring the bridge and using epoxy. I can't see how slicing through the fibers of your sound board would ever be a good idea. Well, at least you'll have a steady stream of work coming in! |
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| Author: | DanKirkland [ Wed Oct 03, 2018 2:45 pm ] |
| Post subject: | Re: Scoring acoustic bridges on reglue |
pat macaluso wrote: I was just referring to scoring the bridge and using epoxy. I can't see how slicing through the fibers of your sound board would ever be a good idea. Well, at least you'll have a steady stream of work coming in! You're right it's a terrible idea to score the top. I was saying it's odd how you posted that and I just that one roll through. Weird timing really |
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