Official Luthiers Forum! :: View topic - Bridge related questions

A couple of bridge related questions that I hope someone can steer me correctly on.

1. I have almost completed my 2nd build and almost put my first back together. On both, when cutting the height of the neck block, I used the starting thickness of the top and did not account for final thinning of the top. As a result, my fingerboard was slightly off the top. To compensate for this, I added a bit of thin veneers between the fingerboard and the top. As a result, I would think that the fingerboard is not only a bit high in relation to the top. but also in relation to the bridge and saddle. So my saddle will likely be a bit taller than normal - not much but a bit taller. Any concerns here? Was there a better solution than adding the veneer strips to support the fingerboard?

2. Second question: I have noticed that the front corners/wings of my bridges have tended to curl up a bit after I sand the bottoms to fit the curve of the top. What should I do to remedy / prevent this?

Thanks, Greg

Author:	GHatcher [ Wed Dec 03, 2008 5:18 pm ]
Post subject:	Bridge related questions
A couple of bridge related questions that I hope someone can steer me correctly on. 1. I have almost completed my 2nd build and almost put my first back together. On both, when cutting the height of the neck block, I used the starting thickness of the top and did not account for final thinning of the top. As a result, my fingerboard was slightly off the top. To compensate for this, I added a bit of thin veneers between the fingerboard and the top. As a result, I would think that the fingerboard is not only a bit high in relation to the top. but also in relation to the bridge and saddle. So my saddle will likely be a bit taller than normal - not much but a bit taller. Any concerns here? Was there a better solution than adding the veneer strips to support the fingerboard? 2. Second question: I have noticed that the front corners/wings of my bridges have tended to curl up a bit after I sand the bottoms to fit the curve of the top. What should I do to remedy / prevent this? Thanks, Greg

Author:	Hesh [ Wed Dec 03, 2008 5:38 pm ]
Post subject:	Re: Bridge related questions
Greg my friend how did you sand the radius of the top onto the bridge? Here is a toot and how I do it on the actual guitar. Please note too that if you have great fluctuations in the humidity in your shop between the sanding/fitting of the bridge and the installing of the bridge things can change as the dome of the top is dynamic with humidity changes. Here is the toot: http://luthiersforum.3element.com/forum/forum_posts.asp?TID=13497&KW=Fitting+bridges#forumTop%22 As for saddle height I like to see about 1/8". When saddles get taller so too will the rotational forces acting on the saddle which can result in a split saddle slot or a bridge prematurely lifting. I would go for a proper neck angle into a standard height bridge. This would mean, I think if I understand your post correctly, refitting the neck be it a dove tail or bolt on until the fret board sits flat on the top with no shim and your saddle and bridge are more within spec. What kind of neck joint did you use?

Author:	elysne [ Wed Dec 03, 2008 5:39 pm ]
Post subject:	Re: Bridge related questions
I make my bridges after I set the neck all in place. That way I have a little wiggle room on the actual thickness of the bridge.

Author:	GHatcher [ Wed Dec 03, 2008 6:09 pm ]
Post subject:	Re: Bridge related questions
Thanks for the replies. Hesh: I sanded the bridge as you did, however, Much time has elapsed between sanding the bridge and completing the finishing of the guitar. I don't have a controlled environment shop, but the house seems to remain in the 40-50% range. I do have a home humidifier that kicks in with the heat in the winter to keep things in this range. This is a bolt on neck , I think the issue is the the position of the bolts. I am using a pre-made neck and block, so I am not sure I have many options unless I decide to ditch the neck and start over. I will go ahead and try to complete these and see if I can make it work with a reasonable saddle height. For the 2nd, I might need to look for a new bridge if I cannot get the wings to uncurl. This is not a lot of curl, but I can notice it. Thanks, Greg

Author:	Hesh [ Wed Dec 03, 2008 6:40 pm ]
Post subject:	Re: Bridge related questions
OK Greg that makes sense. On a pre-made neck with the pre-drilled bolt holes you can use a round file and elongate the holes a tad, probably the same distance as the shim that you used under the fret board. Elongate the holes on the bottom side and with a sanding block and chisel remove about the same distance from the bottom end (curved part) or the tenon. This will let the neck sit further down onto the body and with some trial and error the bolts will fit nicely too. The goal is to seat the neck a bit further down onto the guitar so you don't have to use a shim and this will reduce the height required for the saddle and bridge too. which requires that you elongate the bolt holes. Also, you can also elongate the mortice with a dremel and sanding drum and clean up the corners on the back of the mortice with a chisel. Make sense? One last thing to consider in case we are talking about a symptom and not the real problem. How is the neck angle in terms of where a straight edge placed on the neck's frets comes in over the bridge and what bridge height do you have now? Thanks.

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Author:	Hesh [ Wed Dec 03, 2008 6:45 pm ]
Post subject:	Re: Bridge related questions
Also if you decide to do the above be careful with the file when poking it through the bolt holes in the neck block to not damage the upper transverse brace.

Author:	GHatcher [ Thu Dec 04, 2008 5:45 am ]
Post subject:	Re: Bridge related questions
Hesh: That makes sense. I will keep that in mind as I set up number two. At least a couple of weeks away. On number 1, I am feeling a bit dumb this morning. As I took another look last night, I realized that the issue was not enough clearance for the Truss Rod nut. Once I opened this up with a rasp, that fingerboard set right down as it was supposed to. Thanks for your help.

Author:	Hesh [ Thu Dec 04, 2008 8:08 am ]
Post subject:	Re: Bridge related questions
Cool - well that was an easy fix and good thing you caught it too.

Author:	Alan Carruth [ Thu Dec 04, 2008 4:05 pm ]
Post subject:	Re: Bridge related questions
Hesh wrote: "As for saddle height I like to see about 1/8"." Just to clarify: what's important in terms of both structure ant tone is how high the strings are off the TOP, not how much saddle sticks out of the bridge. I shoot for 12mm, call it 1/2", plus or minus a millimeter or so. If your bridge is 9mm thick then you'll indeed end up with about 1/8" of saddle showing.

Author:	GHatcher [ Thu Dec 04, 2008 9:29 pm ]
Post subject:	Re: Bridge related questions
Alan and Hesh: Thanks for the explanations. I have it strung up and the string are about 11mm off the top. Going by the guidelines in the Kinkade book the action is between low and medium. I am still playing with the setup and may need to dial some relief into the neck, but number one is in much better condition now than before I took it apart and put it back together. As far as the bridge on number two I have a little weight on it trying to take the curl out of the wings. Hopefully that will help a bit by the time I am finished with number two. Thanks, Greg

Author:	Hesh [ Fri Dec 05, 2008 8:43 am ]
Post subject:	Re: Bridge related questions
Yep and I will add that John Hall has in the past posted that Martin also wants to see 1/2" from the bottom of the low E to the guitar top when measured at the face of the bridge.

Author:	Howard Klepper [ Fri Dec 05, 2008 1:46 pm ]
Post subject:	Re: Bridge related questions
Alan Carruth wrote: Hesh wrote: "As for saddle height I like to see about 1/8"." Just to clarify: what's important in terms of both structure ant tone is how high the strings are off the TOP, not how much saddle sticks out of the bridge. I shoot for 12mm, call it 1/2", plus or minus a millimeter or so. If your bridge is 9mm thick then you'll indeed end up with about 1/8" of saddle showing. I've been trying to make sense of this. Some saddle height over the wood is needed for break angle. Some wood height is needed to support the saddle. Some amount of wood is needed for mass and structure. All these have a range of parameters that should not be exceeded. So how is it that only the saddle height above the top matters?

Author:	Michael Dale Payne [ Fri Dec 05, 2008 2:26 pm ]
Post subject:	Re: Bridge related questions
GHatcher wrote: A couple of bridge related questions that I hope someone can steer me correctly on. 1. I have almost completed my 2nd build and almost put my first back together. On both, when cutting the height of the neck block, I used the starting thickness of the top and did not account for final thinning of the top. As a result, my fingerboard was slightly off the top. To compensate for this, I added a bit of thin veneers between the fingerboard and the top. As a result, I would think that the fingerboard is not only a bit high in relation to the top. but also in relation to the bridge and saddle. So my saddle will likely be a bit taller than normal - not much but a bit taller. Any concerns here? Was there a better solution than adding the veneer strips to support the fingerboard? 2. Second question: I have noticed that the front corners/wings of my bridges have tended to curl up a bit after I sand the bottoms to fit the curve of the top. What should I do to remedy / prevent this? Thanks, Greg Reading this I get the impression that the neck fitting (neck angle set) was either misunderstood or non existent. When you fit a neck you fit, in the terms of a pilot, you fit both heading (left to right to match centerline) and attitude (neck pitch up and down to achieve the proper fretboard to bridge plane relationship). Typically the angle of the neck would be 1.5 degrees back but the stack up of tolerances accumulated during the building process can cause this to need to be adjusted during fit up to achieve the proper fretboard/ bridge plane relationship. I will assume you used a bolt on M&T neck. If you over sanded the top to the point that fretboard extension was proud of the top when installing the neck and needed shim. In my opinion the better fix would have been to shorten the bottom of the tenon, dowel plug the neck block bolt holes and re drill the holes lower or elongate them as needed. This would bring the fretboard down to the top for a better fit and fretboard/bridge plane relationship. I can’t imagine the neck being more than 2mm or so proud of the top. The bolt holes in the neck block should have given about 1mm in adjustment down as the holes in the neck block are typically 2mm larger than the diameter of the bolts. So the most that would need to be taken off the tenon would be 2mm and the holes elongated or dropped 1-1.5mm. Tall saddles lead to wear on the saddle slot over time. I had rather have a .75-1 degree neck back angle than end up with a ¼” or taller saddle beyond the bridge.

Author:	Alan Carruth [ Fri Dec 05, 2008 3:37 pm ]
Post subject:	Re: Bridge related questions
Howard Klepper wrote: "I've been trying to make sense of this. Some saddle height over the wood is needed for break angle. Some wood height is needed to support the saddle. Some amount of wood is needed for mass and structure. All these have a range of parameters that should not be exceeded. So how is it that only the saddle height above the top matters?" For once I gave an answer that was too short. You're right, of course, there has to be a certain amount of 'meat' in the bridge so that it doesn't break out in front of the saddle slot, so the saddle doesn't wear through into the top, and so on. My reply was meant to address everything _after_ that; particularly helping the bridge stay glued to the top, and the effect of string/saddle height on tone. If you ignore the break angle (which, quite frankly, I'm not sure how to factor into this, if it even needs to be) the torque will be determined by the height of the strings off the top surface. In this sense, the bridge is a sort of glorified lever, and the longer (taller) it is the more a given string tension will deform the top. More to the point, perhaps, the higher the strings are off the top the greater the peeling stress along the back edge of the bridge will be, and the more likely it will be to pull off. This will be the case no matter how thick or thin the wood of the bridge is. That takes account of the static tension: there's a dynamic tension as well. As the string vibrates it get tighter twice for every full cycle of vibration (once when it's 'up' and once when it's 'down'), and that adds a bit of a tug on the top of the saddle as well. The higher the strings are off the top, the more this tension change signal will be able to move the top and make sound. It's not _very_ effective, of course; the tension change forces are normally smaller than the transverse forces, and bridges and tops are made to resist this sort of motion. Still, it will have an effect on timbre, even if it does not change to overall power output to speak of. So, yeah, you need to stay within 'normal' good design specs with bridges, as with any other part of the guitar, or it won't work. But even within those limits variations will have some effects.

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Author:	GHatcher [ Fri Dec 05, 2008 6:02 pm ]
Post subject:	Re: Bridge related questions
Thanks for all the replies. I will try to clarify a bit. First, I am talking about two different guitars with a similar issue. #1. As I admitted to Hesh in one of the previous replies, the issue on number one was a bit of stupidity on my part. This was a guitar that I built previously and using some advice from the forum, I was trying to repair and make playable. When I was putting it back together, I did not realize that the truss rod nut was not clearing properly and this was causing the neck to not sit down properly. It was about 2mm proud as Michael estimated, but now is sitting just fine. This issue was also throwing off the angle, but now the angle appears fine. I need to measure everything, but I think this one will be OK, but may need some tweaking with the setup. #2. This is a new build. This is the one that I did in fact mis-measure and will be about 2mm proud. To complicate things, I am using some features of the Doolin adjustable neck, so there are pivot points that will no longer line up if I lower the neck using the method Michael suggests. I have already added a layer of veneer to the underside of the fingerboard to fill in the Gap. If it appears that the angles are not correct, I will do as Michael and Hesh have suggested and try to lower the neck by elongating the holes and trimming the tenon if needed. I will also need to plane off the veneer if I go that route. Currently I am trying to get started with the finishing of this one, so I will probably need to get back to fitting the neck and solving this issue after finishing. Thanks for all the feedback. Trying to repair problems on number 1 has been a good learning experience. Greg

Author:	Hesh [ Fri Dec 05, 2008 6:11 pm ]
Post subject:	Re: Bridge related questions
Greg my friend it might be easier depending on what glue you used to install the veneer to remove the veneer with the neck off, placed upside down, and using heat to soften the glue and one to two pallet knives to unglue the veneer. You could use an iron and I would also be mindful to keep the heat far enough away from the neck so as to not unglue the fret board from the neck too in the process.