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| Top collapsing http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=25411 |
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| Author: | jncllc [ Sun Jan 10, 2010 2:41 pm ] |
| Post subject: | Top collapsing |
I'm pretty sure my 1st guitar is imploding. It's dished in in front of the bridge and raising directly behind the bridge. I tried so hard not to overbuild that I ended up underbuilding by scaloping my braces to much(I think). Anyway to fix something like this without removing the top or should I just remove the top and replace it. Its has a cherry red sunburst finish on it and the sides are also stained. I would like to just reinforce it so it would'nt get any worse and chaulk it up to experience and do better on the next one. I've gotten the guitar building bug bad and want to build many more but need to do them more cheaply to get more experience before I build any more as expensive as this one was. |
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| Author: | jackwilliams [ Sun Jan 10, 2010 2:54 pm ] |
| Post subject: | Re: Top collapsing |
I would say that there is probably more at play, structurally speaking than just over scalloping; There is a device out there that is advertised for the exact problem you are describing; I believe it's called a bridge doctor. I have never used one nor am I in any way associated with its owners, manufacturers, or retail outlets, but there are those here on this forum that , I believe, used the product and can more readily attest to the advertising claims . good luck, and best regards, jack |
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| Author: | Darryl Young [ Sun Jan 10, 2010 3:03 pm ] |
| Post subject: | Re: Top collapsing |
Jack, Some of this may be related to low humidity. I see you're in OK......I live in NW AR and the humidity has been in the 20's for nearly a week now. I have a top and back that are braced but aren't yet glued to the rim and each plate has a reverse dome right now so I'm waiting to glue them to the rim when the humidity is around 40%. The back has a 16ft radius and it is slightly reverse domed! One suggestion that will likely help the lift behind the bridge is a PMTE brace. (PMTE stands for Proulx Magic Tone Enhancer which is a nickname for the brace as Mario Proulx uses them sometimes) Anyhow, it is a brace that runs along the rear of the bridge plate between the lower legs of the X brace. I think the brace is typically made using hardwood. This will stiffen the area behind the bridge and may help the tone as well. For the area in front of the bridge, someone more experienced will need to advise. What height and width is the X brace at the intersection? How far from the intersection did you start scalloping the X brace? How thick is your bridge plate, how far does it extend in front of the bridge, and what wood was used for the plate? What kind of top did you use and how thick is the top? |
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| Author: | mhammond [ Sun Jan 10, 2010 3:32 pm ] |
| Post subject: | Re: Top collapsing |
I think Marios invention is wonderful, it will help with the belly and I feel it does enhance the tone. Just search the archives you'll find it.... Good luck, Mikey |
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| Author: | Pat Foster [ Sun Jan 10, 2010 3:37 pm ] |
| Post subject: | Re: Top collapsing |
Mario's PMTE brace is for an entirely different issue. If this guitar is bellying behind the bridge and sinking in front, then it's a structural issue that won't be resolved with the PMTE. A pic would be helpful, also one of the bracing, if you have one. Pat |
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| Author: | truckjohn [ Sun Jan 10, 2010 6:08 pm ] |
| Post subject: | Re: Top collapsing |
Post some pix if you can. Don't go and yank anything apart just quite yet.... All may be OK -- It is a common misconception that a guitar shouldn't display any sort of a belly or any sinks anywhere.... Check out those awesome sounding old Martins and Gibsons... Many times they have quite large bellies and even some pretty good sized sinks in front of the bridge.... Frequently, these sound pretty darn good too! If you have a good way to do it... Measure those bellies and sinks... A "giant looking" sink in front of the bridge may only measure 0.040" deep -- 1 mm or so! Martin's spec for "Too much belly" is in the range of 1/4" -- which is pretty huge... Now, if the sink is 1/8" - 1/4" deep -- sure, be concerned... and at that point you might consider doing something about it... but you still may not have to pull the top... Also, if you can, post a pic of your top bracing -- especially work you did in front of the bridge... Thanks John |
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| Author: | Michael Lloyd [ Sun Jan 10, 2010 6:46 pm ] |
| Post subject: | Re: Top collapsing |
Not sure if this could help. http://www.stewmac.com/shop/Tools/Special_tools_for:_Bridges/JLD_Bridge_Doctor.html?keyword=3694 |
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| Author: | jncllc [ Sun Jan 10, 2010 6:48 pm ] |
| Post subject: | Re: Top collapsing |
Here's some picts. The way I noticed it was it seemed my action was getting lower. I got to looking at it and there it was. I forgot to take picts of the top braceing. What I think I did wrong was I scaloped the x braces above the bridge also. Sure had a nice bell sound to it though.Behind the bridge it dips from the edges then raises at the bridge. In front it does the same only mostly dips. |
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| Author: | woody b [ Sun Jan 10, 2010 7:17 pm ] |
| Post subject: | Re: Top collapsing |
What I see, or at least I think I see in the pictures is humidity issues. I suspect the guitar is dried out some. |
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| Author: | Dave Livermore [ Sun Jan 10, 2010 7:25 pm ] |
| Post subject: | Re: Top collapsing |
shucks, that's nothing... I'm with those who say, don't do anything rash. where's your humidity right now, and where was it when you built the guitar? Get that humidified and see what happens. Dave |
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| Author: | jncllc [ Sun Jan 10, 2010 8:10 pm ] |
| Post subject: | Re: Top collapsing |
It stayed in the house all summer with finish on it but not put together. I took it out and finished it this fall. Started it last spring and quit working on it in the suummer because I got too busy working and it got too hot and humid in my shop(it's only heated not cooled).And I also went fishing every chance I got. I won't worry about much then just keep an eye on it for now and go ahead and keep planning the next one. |
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| Author: | cwood8656 [ Sun Jan 10, 2010 11:22 pm ] |
| Post subject: | Re: Top collapsing |
Looks like low humidity issues to me. I'm fighting that every day here in my shop in northern New Jersey. When you have a chance, go to the Taylor guitar web site and look at Bob Taylor's videos about humidity, they really opened my eyes. Chris. |
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| Author: | Alain Moisan [ Mon Jan 11, 2010 3:39 pm ] |
| Post subject: | Re: Top collapsing |
Dave Livermore wrote: shucks, that's nothing... I'm with those who say, don't do anything rash. where's your humidity right now, and where was it when you built the guitar? Get that humidified and see what happens. Dave Ditto. |
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| Author: | Michael Dale Payne [ Mon Jan 11, 2010 4:00 pm ] |
| Post subject: | Re: Top collapsing |
I am with Pat here! While humidity could be playing a roll but I have serious doubt to humidity being the base cause, What I see is the common result of an under built structure for a new guitar. The same issue is often seen on a decently structured guitar after 60 years of continious string tension. It appears by the photos that the neck block is rotating in as well as I see an inward dip from the sides of the upper bout to the fretboard extention. This rotation of the bridge is the normal tendency of the force load. the fact that it has already appeard this early in the life of this guitar points to structural issues. I notice that the string height off of the frets seems very high as well. At the age of this guitar I am fairly confident in thinking you have a structural issue. What is the top thickness? what is the bracing thickness and height? What string gauge are you using? What neck block dimensions and structure did you use? |
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| Author: | jncllc [ Mon Jan 11, 2010 4:01 pm ] |
| Post subject: | Re: Top collapsing |
I watched Taylor's video and think you're all right about the humidity. It looks just like that. What"s a easy way to rehumidify if I don't have any of those dampits and I don't have a good case for it yet. I do have an old case for my fender 12 string but its falling apart. What kind of humidity control do some of you recommend to your clients? |
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| Author: | Alain Moisan [ Mon Jan 11, 2010 4:19 pm ] |
| Post subject: | Re: Top collapsing |
There is a belly behind the bridge, but nothing out of the ordinary, IMHO. What seems to be caving in in front of the bridge is actually signs of the entire top caving in. You can actually see it caving in as well on both sides of the belly behind the bridge. This really seems to me like dryness issue. In any case, don't ever remove the top or do anything for that matter unless you have serious playability, sound or structure issues (cracks). As mentioned in earlier responses, a deformed top does not mean a problem guitar. Regarding humidifying, what I do is put a wet spong in a tupperware small enough to go through the soundhole and leave the guitar in it's case (flat) for about a week, making sure the sponge is quite wet everyday. Good luck! |
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| Author: | Michael Dale Payne [ Mon Jan 11, 2010 4:27 pm ] |
| Post subject: | Re: Top collapsing |
jncllc wrote: I watched Taylor's video and think you're all right about the humidity. It looks just like that. What"s a easy way to rehumidify if I don't have any of those dampits and I don't have a good case for it yet. I do have an old case for my fender 12 string but its falling apart. What kind of humidity control do some of you recommend to your clients? Mind you I doubt that humidity is the main issue here but re humidify is the first thing to do if you are in an extremely dry environment. Take a plastic butter tub and put a damp sponge in it and place it inside the unstrung body. Place a trash bag over the body and seal the best you can with masking tape. place the guitar in a constant temp location. Check on it every other day for a week to 10 days keeping the sponge damp but not soaked. After that week to ten days, if it has not returned to the near normal unstrung state then you should know if the issue is structural or purely humidity related. |
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| Author: | jncllc [ Mon Jan 11, 2010 4:39 pm ] |
| Post subject: | Re: Top collapsing |
Michael, I used LMI's dred plan PL 48 and made a template out of posterboard that I traced out from the plans useing a light table. They also had profiles of the scalops which I drew on to the sides of the braces. So I followed that at first but it seemed kind of dead so I tapered the sides of the braces. I also scaloped the x braces on the soundhole side and that may be the main problem coupled with low humidity. The braces are 5/16 thick the top was approx. .110" it's a bearclaw stika. My fret board falls off too much now also (now that I look at it) but the top is diving down there too pulling the fret board with it. The back is also doing the same thing as the one on Taylor's video and those braces I did to plan useing the tall thinner style rather than the short fatter type. |
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| Author: | Michael Dale Payne [ Mon Jan 11, 2010 4:45 pm ] |
| Post subject: | Re: Top collapsing |
jncllc wrote: Michael, I used LMI's dred plan PL 48 and made a template out of posterboard that I traced out from the plans useing a light table. They also had profiles of the scalops which I drew on to the sides of the braces. So I followed that at first but it seemed kind of dead so I tapered the sides of the braces. I also scaloped the x braces on the soundhole side and that may be the main problem coupled with low humidity. The braces are 5/16 thick the top was approx. .110" it's a bearclaw stika. My fret board falls off too much now also (now that I look at it) but the top is diving down there too pulling the fret board with it. The back is also doing the same thing as the one on Taylor's video and those braces I did to plan useing the tall thinner style rather than the short fatter type. I hope I am wrong for your sake and that this is all humidity or lack there of for your sake but that is a lot of rotation at the bridge that has accrued. I live and build in a very dry climate and I carry my guitars all over the world. I have never had one move this much from coming from a prolonged stay in a damp environment and coming back hole to my typical 30% environment. Anyway the first thing to do is to re-humidify the body. |
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| Author: | jncllc [ Mon Jan 11, 2010 4:49 pm ] |
| Post subject: | Re: Top collapsing |
What do you mean by bridge rotating? It's definitly rotating down towards the sound hole in front and raising in back. |
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| Author: | Alain Moisan [ Mon Jan 11, 2010 5:00 pm ] |
| Post subject: | Re: Top collapsing |
jncllc wrote: ...It's definitly rotating down towards the sound hole in front and raising in back. Yep, that's it. But it all depends on how intense the rotation is. As Michael pointed out, your strings are indeed quite high over the fretboard and the saddle seems pretty high as well. That will increase the torque the strings apply on the bridge, thus favoring such a rotation of the bridge. But as Michael pointed out, first off is to rehumidify your guitar. The fretboard extension plunging in is yet another sign of a top collapsing, by the way... |
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| Author: | Michael Dale Payne [ Mon Jan 11, 2010 5:03 pm ] |
| Post subject: | Re: Top collapsing |
jncllc wrote: What do you mean by bridge rotating? It's definitly rotating down towards the sound hole in front and raising in back. The string tension causes the bridge to rotate. The axis of this rotation is the saddle. The bridge rotates inward on the sound hole side and upward on the butt side. this is what cause the the bridge to rise in the rear and sink in the front. this is the expected affect of caused by the force of the string load on the saddle and bridge and bridge plate. What your guitar is doing right now is exactly what every guitar will do over a given amount of time under a given amount of string tension. the string tension has the same affect on the neck block. Pulling the nut and peghead upward and forward which drives the neck block to rotate towards the Sound hole. this is all basic reaction to the force of the string tension. this is what eventually leads an older guitar to need a neck rest. The geometry of the body and neck changing over time due to the constant pull of the strings on the structure. |
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| Author: | Darryl Young [ Mon Jan 11, 2010 8:14 pm ] |
| Post subject: | Re: Top collapsing |
What gauge strings are you using? If you are using mediums, you may want to consider switching to lite gauge. |
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| Author: | bluescreek [ Mon Jan 11, 2010 9:02 pm ] |
| Post subject: | Re: Top collapsing |
I am with Michael here and I think it is more than humidity. Blue prints are just drawings , but as a builder you need to understand all the forces involved on a top. Yes there is a chance it is RH but if you tried to rehydrate it and it didn't help you may have more going on. Too often the scalloping that newbies do is too severe . I suspect you over scalloped it . Look at your top and understand this is something I learned from my experience . Between the bridge and the neck block there are 2 forces happening . There is a compressive force between the neck block and bridge from the tension of the string ., Also this force causes a rotational force to the neck block and bridge . If you over scalloped braces you lost the support around the soundhole and the top caves in , and the rotation will happen. I hope your issue is humidity and that it isn't an underbraced situation |
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