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Hello,

Recently I have been building in batches to test the efficiency of my process, it also helps to further reinforce learning by repetition. This has been pretty effective, but I have run into something interesting that I am not equipped to explain. I am setting all of the necks on the 3 builds that I have going. I have been using some fret wire with the tangs filed off to measure the bridge thickness. I have come across something weird, two of the builds have very close to the same bridge thickness and one is about 1/8 thicker than the others. I am building them all in the same fashion, same fingerboard thickness, same amount of fall away on the fingerboard. The bridge thickness difference still remains. I did use Hesh`s tuts in order to flatten the upper bout. This is the only area I think that could explain the bridge thickness difference. Maybe I sanded more on this particular build than others? The only issue with that theory is that I used pencil marks on the whole upper bout area and stopped sanding as soon as it removed all of the pencil marks. Any input would be very helpful, I am lost.
The guitar is a cocobolo and cedar top cutaway. Since it is a cedar top, the added mass to the top including the increased torque due the added height may have a negative effect on the tonal and structural characteristics of the cedar. This particular piece of cedar was incredibly stiff across the grain and along the grain. It is stiffer than most of the spruce I have across the grain and has similar stiffness length wise as most of my spruce. If you could please offer some insight on that area that would also be greatly appreciated. Thank you so much for reading

Robbie

The only reason I could see for a difference needed in the height of your bridge would be the angle of your neck. Assuming that your top is square to your sides, it must be your neck set angle. Most necks set back at about 1.5 degrees (depending on how you build). Check that angle on all three and see if they are the same. If they are, you have me stumped.

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Even the factories have problems with this. How does the dome on the tops compare to what you intended?

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oddly enough the dome on the cedar guitar is a little more prominent than the others which only confuses me further. I do not have my angle gauge with me so I cannot check the angle, but something tells me that the only thing it could be is, I just must have went crazy flattening the upper bout on this one. If the angle is more significant this would prove that the upper bout area has been lowered further than the others. If the upper bout area is to blame and my bridge thickness is necessary, would this bridge thickness have an adverse effect on the tone and structure?

I think "neck angle" is misunderstood by a tremendous number of people. Chris is right to qualify it by saying "assuming that your top is square to your sides" but that is a big assumption and hard to know if you dome the rims. But in reality, the angle of the the sides meeting the top doesn't have any bearing on it. It can be anything. What you are concerned with is the plane of the top from the heel to the soundhole and how it projects to the bridge. If that is off, there is nothing you can do short of shimming the fingerboard extension or changing the height of the saddle/bridge. That is the only thing that determines the bridge height, assuming a given amount of fallaway and a parallel fingerboard.

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To add to what Kent says, getting carried away while sanding the upper bout flat could net you significantly more than 1.5° while still providing the correct relationship between the plane of the fretboard and the bridge. DAMHIKT.

Pat

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I see what are saying about the relationship between the two planes and quantifying this relationship with a dimension is meaningless unless my relationship correlates with "standard" building styles. In my situation would it be correct to conclude in order to reduce the bridge height I need to change my neck angle. In changing my neck angle I will subsequently lose my current set fall away. If further adjustment is needed I would end up with up a fretboard extension that would project upwards due to the angle change. If I choose to adjust the neck angle and end up with a fret extension projecting upwards, I could rectify that issue by leveling the fretboard. If I did so the fretboard would lose thickness mostly on the end of the fretboard extension which would be unpleasing to the eye. If I choose the original neck angle that maintains the correct fall away and increased bridge height at .43 or 10.92mm what would be the result of that? Thank you guys for choosing to school this newb.

Robbie

Robbie,

If the end of the fretboard extension ramps up, you can also taper it a bit from the bottom.

Pat

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It seems to me that if I were to go that route I would have to take off a significant amount of material in order to get the bridge down to around 5/16. Is a bridge being that thick enough of an issue that tapering the fingerboard is necessary?

If you are trying to lower the bridge, I would consider a wedge shaped shim under the FB extension. If it goes from being thicker at the heel to thinner at the soundhole, that looks fine to my eye. In fact, I used to build like that intentionally. Most people never even noticed it.

There is a recent thread about bridge/saddle height that has more info to answer your question about going with a .43" bridge. In brief, if you add 1/8" of saddle to that, you will will be a bit under 9/16". The extra height will put more torque on the top (approx 12% more than at 1/2"). The effect of that will vary depending on your top. It could improve an over-braced top or it could kill an under-braced one.

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Thank you!!! Now I get what your saying. I am sorry I tried to search prior to asking the question. I will take a little off of the end of the fret board and a little off of the top of the heel and add a shim to the underside of the fret board. It should only be about a 1/16 at its widest point so it won't be too noticeable.

Just a thought, if you taper your fretboards with a table saw jig save the off-cuts. they make great tapered shims if you need to prop up the end for some reason. Invisible if Ebony.

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I am very familiar with Martins assembly and they don't have a problem. In fact they have the process dialed in very well. Having the sides set up for the neck angle is a big help . To help get your mind around this principal think of the final target. The bridge and saddle height on a Martin style build will about 1/2 inch.
There are many ways to set this up. I use the concave disk at 28 foot. This incorporates the angle into the sides. I don't radius the entire top just the area above the soundhole and the lower bout. When I am dry fitting the neck I want the line from the neck plane to be at least 1/16 in above the top to 1/8 in. This the the plane of the joint of the fretboard and neck. I am using a fretboard that is 1/4 in thick at the center.
You need to create this plane so the fretboard will be true. If you over sand this you can have gaps at the joint , or ski the fretboard. You don't want to use a shim on a neck set on a new build if you can help it. Here is a vid link to help you see what I do and how I do it.
http://www.youtube.com/watch?v=LrgRKKsxL-M
hope this helps

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John Hall
blues creek guitars
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A .43" thick bridge is going to be a big heavy tone sink. If the torque on the top caused by the extra string height doesn't cause structual problems I suspect the tone will be kinda....thuddy. A finger board that's thinner at the end won't be noticable at all. Some Huss and Dalton models are that way. A change in angle that would require the fingerboard to be .040" thinner at the end would make a big difference in bridge thickness. (~.100")

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It almost sounds like the top picked up extra dome somewhere....

Possibly it was extra dry when you braced up that one?

As a few here have suggested -

Adjusting the fretboard's taper is a Fairly standard way to get the action on a Classical sorted out.... since the neck is glued to the body early in construction...

Alternately, try making a tapered shim to fit under the fretboard extension - then you can re-set the neck angle at the neck heel so that it fits with the right size bridge...

Thanks