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Hi Guys

HAPPY NEW YEAR to you all.

I had a guitar I built come back to me to have the action lowered. When i saw it I couldn't believe it - the action was much higher than I'd originally set up? The guitar is played and gigged regularly and the owner loves it but It's less than a year old!!

Anyway, I took the neck off (my first ever - why, oh why did I glue in the mortise and tenon!!) and it was a great success. I followed Hesh's toot and sanded the heel to a better angle and have now got the action perfect and very low.

However, my real concern is 'What's happening'?? and will it happen again? I'm thinking that the Redwood top is too thin but I don't know what I can do about that now. The guitar is always strung up with Light strings.

Do you think I should put in a Bridge doctor? Would that help? I don't really know if the top was bellying that much but I guess it must have been.

Any advice greatly appreciated.

Mat

I don't know what others think but I would suggest that the short grain in the curly redwood top does not offer the longitudinal stiffness required to counteract the pull of the strings. Unlike a straight grained top I suspect the short grain is acting like a concertina and will continue to unfold under the strain. I would think a F Dr may be the only way to avoid even more catastrophic bridge roll in the future, but then again, maybe not.

Cheers

Kim

well you need to investigate the geometry of the guitar to see where it moved, how is it now compared to when you sent it out ? could be too thin a top or weak braces, could be the neck block moved. could be the top sinking in at the transverse brace. could be the guitar was stored somewhere with high humidity .how is it different now than when you sent it out ? Jody

Happy New Year, Matt, and welcome to the wonderful world of resets!

Did you see bellying when you strung the guitar up, after the reset? It would have to have been obvious and serious. A JLD will certainly stabilise that top, and, if installed correctly, give a significant increase in volume and sustain. So, it can't hurt, and can certainly help; I suggest using a strobetuner when you're adjusting the JLD.

I don't think a bellied top caused the neck angle shift. Resets just...happen--when I was repairing through a store, I'd see 1-2 year old Martins with lousy neck angles.

Bottom line--your client loves the guitar!

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https://soundcloud.com/jeffreylsuits/he ... -runnin-13

So you didnt check out the guitar geometry before taking the strings and neck off ??? Hmmm .... dont do that next time before a complete evaluation - thats how you will learn about what went wrong - all we can do now is speculate.

If the top is bellying behind the bridge - and caving in front of the bridge, then there is certainly reason to suspect the FB ext is caving too. How big is the UTB ??? was it flat or radiused prior to gluing in ??? Was the top radiused or flat ??? what was the FB lie when you completed the guitar - just above the bridge ??? how much saddle was showing ???? You may not know the answers to these questions, but they can lead us to see how and what went south. ....

As for the JLD increasing volume and sustain, Mario Proulx has installed a number of these into bellying gutiars, and it was always to the detriment of the guitars tone in his opinion. I fail to see how restricting the tops movement (which the JLD will do somewhat) is going to increase anything, unless the guitar was designed to have the thing in there in the first place.

So back to the guitar itself ... my guess is that the whole thing started to cave under tension - it just took time from when it left the shop. Could be the top was thin, or simply weak, or the bracing too small as well. Lack of humidity could have played a role too - guitar gets a little dry, the guitar top flattens, the action rises and the string tension exerts it force causing the top to flatten more and so on ... the wood settles to this state and it never comes back.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Guitars are a fascinating machine. What happened to your guitar is at best a guess without a hands on inspection. The geometry of the guitar is a fascinating study and one you need to understand.
The stresses on the top come from the strings but you need to understand the way they are applied to the top and what happens where. In most cases the neck block rotates from the stress of the strings , This flattens out the back a bit and can make the top sink in the area of the sound hole.
you never told us what your bridge height was and what the plate was. You other area of stress is the bridge , and that can rotate causing the top to sink in front of the bridge and pull up the lower end of the top. All of these end results may be from bracing failure , too light of a brace , top not matched to the bracing for stiffness etc.
You may have just over looked the initial set up and set the neck too low. I don't think anyone can tell you what happened without a good hands on inspection. I kept building logs so that I could go back and see what each guitar did over time and how they were braced , top thickness and deflection of the top and back. You need to be scientific so that your deductions are based on fact not opinion. That is one of the hardest things to master. Often we think we understand only to find out we didn't know as much as we thought.
Good luck and enjoy building
As I often say " you will learn more from a failure , than you do from a success"
john hall

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for your replys

I've just had a look at the top since it's been re-strung (but I haven't glued the FB yet).

The top seems to be bellying quite severely behind the bridge and the FB is sinking towards the soundhole. The more I look at it and think about it the more depressed I'm becoming.

The top was radiused. The UTB was flat (if I remember correctly) and about 1/2" in height. There was only a little saddle showing.

JOHN - The bridge was actually a little low in the first place by 2-3mm. I would be prepared to replace the bridge but if the bracing is all wrong....... etc etc.



Is this fixable??

its all fixable, if you are warranteeing your work , it may call for a new top.its a big loss, but your reputation is worth it all. Jody

Matthew my friend there are a bunch of things that I would want to know before I even ventured a guess here. How about some details for us so we can assist you better?

1) redwood top - how thick is/was it?
2) was this the one that the bracewood came from a respected Canadian supplier (I searched the archives to see if there were any construction pics of this guitar) and you did not know if there was any runout?
3) are there any loose braces in the box now?
4) You mentioned that the bridge was 2-3mm low to begin with - that's a lot...... and further mentioned that you still had some saddle showing, how much? It's possible that the neck angle was never right to begin with with this low bridge and saddle and the structural weaknesses of this top and bracing moved the strings even higher.
5) Do you have any pics of the bracing before you closed up the top?
6) Was the bracing scalloped and if so how low did you go at the low points?
7) Any chance the player slipped some mediums on there without telling you?
8) What glue did you use for the braces?
9) Bridge plate - did it extend at least 1/8" in front and behind the shape of bridge that you used AND is the bridge plate in the right place?

That is all I can think of for now..... But these guys will have a far better shot at answering your question here with some more info from you.

And of course I am sorry that this happened to you.

I had a 10 year old guitar come back recently with complaints of really high action. I looked at it and the top had a huge but even dome and no dipping around the soundhole. I started asking questions and it turned out the guy had been living on his boat with it. Probably 80 - 90% RH. I kept it im my shop for a week and it dropped enough that I just needed to lower the saddle a bit and remind him to keep it within reasonable humidity ranges.

So along with all the structural stuff, check the humidity too.

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http://www.chassonguitars.com

Guys - I can't see that humidity was a problem. The guitar was kept in a hard case in a normally heated home.

Hesh - The Redwood was thin, about 3mm and probably less after my rough sanding!! (yes i know that's a ridiculously thin top for Redwood but before finding the OLF I based everything on my limited knowledge of following a 'how to build' book which didn't deal with any variables).

I think the braces are ok but even after reading all the threads and hand splitting my own braces I still don't know how to read run out

The braces are glued with Titebond. I think they're reasonably well scalloped except I noticed that the x was not capped - I cap all of my x's now but only since joining the OLF!

The bridge plate is maple - although it was an off cut from a back and may not have been stiff enough. It is however in the correct place and oversized.

The neck was almost definately not set correctly in the first instance

Thanks

Matthew,

Really sorry that this happened. As previously stated, you will learn a lot from evaluating and fixing this guitar so look at it as a positive experience overall.

Reading John's post has me thinking (scary at my level of experience! <smile>) Wouldn't a short brace connecting the neck block and the transverse brace (and glued to teh neck block, transverse brace, and top) significantly stiffen things up and help resist rotation of the neck block? You could either use one brace down the centerline of the top or even better, use two braces running directly beneath the edges of the fretboard extension. Seems it would add very little weight yet add significant stiffness in the direction that would resist rotation of the neck block. Any thoughts from experienced builders?

Maybe stiffening this area and then beefing up the soundboard around/under the bridge will have this guitar singing again.

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Formerly known as Adaboy.......

Mat,

It would help if you could post some pictures of the top's geometry under string tension as you have it now. Some shots of the bridge from the side and the bridge, soundhole, fingerboard area would be useful. You say the top behind the bridge is bellying (not necessarily a "bad" thing) but what is happening in front of the bridge? Also how tall is the bridge and saddle? The soundhole area is a key one structurally and you could fit a re-enforcement cross grain patch in the pentangle brace area of the soundhole, but if the upper bout area isn't braced enough to take the neck compression then this on it's own won't be enough. As I say some pics would help a lot.

How does the guitar sound by the way one year on?

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Matthew thanks for the additional information and pic!

From the pic that you just posted it's difficult to tell if you have radiused the top and braces - is this a flat top or is there a radius built into the bracing and top?

Although my friend Dave and I have gone rounds on top thickness before on another forum it does, to me, without having any deflection testing data, sound like this top is thin. Although this can be countered with more bracing it's hard to know from a picture if your bracing is substantial enough and if the bracing stock was stiff enough to work well.

It always fascinates me that when we string up our creations the top will rise a bit under string tension if we built it in such a manner to do so. I have heard Mario describe a top as not unlike a spring which I think is an excellent analogy.

What I think is happening here is that the neck was under set originally meaning it's angle was not high enough over the top and intersecting the bridge top or slightly over it. This in and of itself would make the action difficult to get down. The bridge and saddle are too low, you want to see about 1/2" between the bottom of the low E string and the guitar top measured at the leading edge (face) of the bridge.

Combine an underset neck, low bridge and saddle, and perhaps, I say perhaps because although I suspect that your top is thin we can't know if this is a stiff top or not, a top that moves excessively under string tension and you have the makings for needing to do a neck reset and of course high action.

How do you prevent this from happening again? You could see how the guitar does with the proper neck set/angle, repair or replace the bridge and saddle to get them into spec and possibly get lucky or you may need to replace this top.

I would not go the JLD route because the expectation must be that this is a fairly new guitar and should, as such, perform like one.

Hesh - The top x bracing is radiused to 28'. I don't think it is under braced but as to the strength of the braces
I have reset the neck but the strings fall short of 1/2 from the top. they are now at 3/8" (10mm). If this is too low I would be prepared to make a new bridge if that was the answer.

Dave - good to hear from you again. I have attached some photo's. #1 is the belly behind the bridge
#2 is the sinking towards the soundhole
#3 is the view infront of the s'hole -just a slight belly
#4 is the bridge. It is approx 61/2 - 7 mm + saddle

[quote="Dave White"]How does the guitar sound by the way one year on?

That's the annoying thing. You met the owner at Cheltenham this year. He played (and loved) your guitars. He has a Taylor, a Thornbery and a Lowden but he plays mine all the time. I can't describe how she sounds but he loves this machine.

thanks

Matthew,

I hope you don't mind me asking a few questions so I can learn how to correct this type issue.

Possibly I misunderstood the suggestions.....but wouldn't making the bridge/saddle taller just make this situation worse? Seems it would lengthenteh lever arm increasing the torque causing teh bridge to rotate further. Where am I off-base? It would be a good thing if the top was thick enough and braced sufficiently to support the taller bridge but it seems this guitar probably has great sound and is right on the edge of not supporting the string tension as is......which probably makes a great sounding guitar.

Matthew, do you have a 28' radius caul to lay over the top and snap a picture? Wouldn't that reveal the true deflection caused by loading the bridge?

_________________
Formerly known as Adaboy.......

Hi Mat,

I'm sure the repair guys will chip in here and other more "experienced" builders but I'll give you my 2p's worth. The belly behind the bridge and just in front doesn't bother me at all - as you know I like my tops well domed anyway Also the bridge doesn't seem to be collapsing into the soundhole and tilting forwards - so the JLD bridge doctor is not necessary or useful here imho irrespective of it's tonal impacts. If the guitar is giving good tone and volume with that height of bridge and your new neck set gives a good playable action then fine - the lower string height is putting less torque on the top anyway. Your problem is in the soundhole area and probably the upper bout area.

As Simon likes the guitar I'd go for what fixes you can do and leave a top replacement as a future option if implosion looms - not a big deal anyway. I'd put a cross grain patch in the area of the pentangle braces surrounding the soundhole. I haven't done one as a repair as I put them in on all my builds but suggested this method on another Luthiers Forum that was used by someone and worked: Play around with cardboard templates until you get it to fit (or measure one from your plans if you used some). Make one with a centre hole taken out so that you can get your hand inside the box to check fit. When this fits hold it in place and mark where the soundhole goes and cut out this template with the soundhole out. Mark this on more card - the outside edge and the soundhole. You can then find the soundhole centre. Use this template to mark the centre hole and outside shape on your piece of spruce/redwood. Use your circle cutter to cut out the soundhole area and then cut the outer pentangle edges. Check for fit and you should then be able to glue it on with small plastic clamps around the soundhole edge.

You'll also need to strengthen the upper bout areas and repair guys like David Collins/Howard Klepper may be of more help here. If there is space you may be able to fashion an extra UTB that can be glued in - getting the ends in the linings may be tricky though.

If you take the string tension off, what does picture 3 look like? Is there still a dip lengthwise on the top? If so you may have to use the internal brace repair jacks to get the shape back when doing brace fixes in the soundhole utb area.

Oh - and it's pretty easy to put a cap on the X brace joint now too.

Paging David Collins/Howard K !!

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Thats one of the reasons I won't use any curly redwood tops by itself. Seen several with major bellying.
I will do double tops or my own semi-double design created specially to address the weakness of the Curly Redwood tops.....

_________________
Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

I see one area of concern on the top. I see that you scalloped the braces. It also appears that you scalloped the braces at the area they needed the most stiffness. I see you have the scalloping under the bridge? This is a area that has to be able to stop any rotational force.
The dipping at the fretboard isn't too much out of the ordinary but the raised area and the deflection right behind the bridge is pointing to under bracing at the bridge. With as much distortion on the top and you said the bridge was low to begin with tells me that you didn't have enough strength at this point.
I never scallop my X braces until I am behind the bridge pins at least. You may be able to rebrace the top or use a bridge doctor.
john

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Mat thanks for the additional pics.

The amount of distortion that I see around the bridge does bother me. Different strokes for different folks. And this is really a new guitar too - less than a year old.

If you go the route that Dave is recommending while you are in there and without the string tension on the guitar cap or install a cloth patch on the X intersection too.

I think that Darryl is correct that a lower bridge exerts less torque on the saddle, bridge, and top. But even with a bridge and saddle height of 75% what it should be the top is distorting......

I don't see the logic in reinforcing something that is out of spec to be out of spec and IMHO likely to need to be revisited again. If it were my guitar I would replace the top if you don't want to be fixing this one again or resetting the neck again in short order.

John,

Good point about the scalloping near the bridge. I admit to having no experience of Bridge Doctors but thought they were mainly used to fix/stop the forward rotation of the bridge not just cure a behind the bridge belly. Lots of pics of pre-war Martins that I have seen show the sort of belly behind the bridge in Mat's pictures but with the bridge not rotating forwards, and they are cannons - so I hear.

Whacky thought I know but an English builder - David Anthony Reid - makes scallops in his braces and then caps the peaks with a spruce strip. His theory is of stored energy. How about making two spruce strips and gluing them to the two peak peaks of the X brace scallops where the bridge is - similar principle to capping the X brace join I suppose.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

First thing I would do is cap the x brace intersection, and I would not use cloth.
If the section is still flat at the intersection, I would use 1/8' thick spruce 1.5" long.
If rounded, I would use some Carbon fibre or glass fibre cloth and epoxy on the member which is notched at the top.
I would prop it up near the intersection to at least level while glueing the cap.
Check that the upper transverse brace is still flat across the guitar.
Has it been weakened by an oversize truss rod access hole/ rounding off of the brace top etc

Capping the braces won't help, In all my years of repair I have not had to repair a cloth joint but have seen capped ones fail. Remember that a braces is carrying a load differently to a floor joist.
The structural strength of the braces have been compromised and need to be addressed. Wood can take more load tensionally then compressive. The bridge load on the strings are rotating the bridge. With the scalloping under the bridge the strength is not there to counter the applied force and this is one of the reasons that it is failing. Adding a spruce top will not add enough strength where it needs to be. Wood shape , is one of the ways to influence this.
When you look at the bridge and applied forces to the top you have 3 forces being applied, From the bridge forward the load is compressed and under the bridge you are seeing rotational force. Behind the bridge is tensional .
Wood will be stiffer in its shape. Figure to the cube of the height. There was an interesting article about this in one of the past guitarmaker magazines. I am sure one of the members can find it.
john

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I would not expect that a Martin style cloth patch would fail, there would be too much give in the fabric. But also not the best for structural support.
A properly installed cap will near double the stiffness of the intersection.

All the cap does is add more mass. There is some stiffness add but it isn't where you need it. Structurally braces are not beams. If you want to use a cap and you feel comfortable with one by all means use it. It isn't adding support where you truly need it. You are using the brace to control rotational force that is applied under the bridge , the force at the X joint is a compressive force. The vibrations also apply a shear force to the glue joint any time it is moved and this can cause a glue joint failure.
I must ask you as to why you feel you need this? I am playing devils advocate here and maybe you can offer me some information that I havn't heard.
thanks
john

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it