Tone bar braces

[watergunn]

Hi all.

On your tone bar braces. What is the height that you should shave the lowest point to between the peaks?

I have a set of Martin braces and the lowest point on the tone bars is 6.5mm. I have always shaved them a bit lower myself.

Just curious how high others do this.

Thanks

[Ben-Had]

I never measure mine but I'm am pretty sure they are in the 4 mm range (I say that because they are a little thicker than the tucked end of an X brace). I keep trimming them until I get a tap tone sound I like.

[tippie53]

Mine tend to run between 1/2 in to 9/16 high and 1/4 to 5/16 wide. If I scallop I will take about 1/3 to start on the 1/4 and 1/2 of the 5/16 .
I am not a tapper I use a weight and measure deflection , the key here is to find it to do what you want it to do.

[Ben-Had]

Mine tend to run between 1/2 in to 9/16 high and 1/4 to 5/16 wide. If I scallop I will take about 1/3 to start on the 1/4 and 1/2 of the 5/16 .
I am not a tapper I use a weight and measure deflection , the key here is to find it to do what you want it to do.

That's pretty interesting John - one half of 5/16 is .156" (yours) and 4 mm is .157" mine.

[tippie53]

I guess you see I don't use mm much LOL

[Darryl Young]

One of you is way off!!!

<smile>

[rienk]

Mine tend to run between 1/2 in to 9/16 high and 1/4 to 5/16 wide. If I scallop I will take about 1/3 to start on the 1/4 and 1/2 of the 5/16 .
I am not a tapper I use a weight and measure deflection , the key here is to find it to do what you want it to do.

That's pretty interesting John - one half of 5/16 is .156" (yours) and 4 mm is .157" mine.

I think John is talking about width being 5/16, and Tim is talking about height?
For clarification, it might be good to state the height of the top of the scallop, as well as the bottom of the valley (I don't know what you call it).

[rienk]

Mine tend to run between 1/2 in to 9/16 high and 1/4 to 5/16 wide. If I scallop I will take about 1/3 to start on the 1/4 and 1/2 of the 5/16 .
I am not a tapper I use a weight and measure deflection , the key here is to find it to do what you want it to do.

I've seen data (and video) on how much deflection to have in a top when thickness sanding, but I have not seen anything about what it would be with the bracing.
Is there any information available about what deflection should be in various axis of a braced top?

it would be great to know what those measurements would be (especially for newbies like me who don't trust their ears).

Since I am planning on building using truss style bracing, the only thing I can directly compare will be deflection measurements, so any help would be greatly appreciated!

[tippie53]

Bracing a top I want to know the stiffness pre brace so I can adjust the the braces for the end stiffness. I also want to know the weight. Since the top is the main contributor to tone the way the top works is the end result of the guitar.
I suggest that you need to keep a log , and with that you can create a log of information and get a ratio . Do start your chart or log , you need to make parameters. Be consistent on measuring. You need to start with a top and decide if you use a thinned top , or work with the weight .
Have a set distance and weight and you can make a map of the top and measure the top deflection with the given weight.
Then decide if you manipulate the top bracing for a given movement of weight and where it moves. Once you do this you can create a base line data line and the top differences of movement and pre brace post brace movement.
Now you can assign a number and use that information of the end result and what and how that information influences the end result on tone.
There are any number of ways to document information in a top, it is up to you as a builder to apply the science of the top for the end result you are looking for. Tapping and using an ear is subjective information.

[tippie53]

I want to add a point
Yes my tone bars when I scallop will be about 5/16 off the top.

NOTE:
Tops will have a few different forces applied to the top . Use that information to your advantage.
Also if you keep detailed measurements on deflection , you will see that the deflection changes from a free top to one that is glued to the sides.

from the bridge to the neck block there is a rotational force applied from the bridge and the neck block. There is a compressional force between the bridge and the neck block and a tensional stress from the tail to the bridge.
Things will be able to take more stress under tension than compression , and compressional force will compound with the rotational force so you want the bulk of the brace mass here. I have seen guitars with scallops on the upper part of the braces fail rather quickly.
Behind the bridge you can work with the bracing scheme more in scalloping. Again keep this information in your building log.

NOTE:
any sharp corner can become a stress riser , in braces you will want to radius any sharp corner. I like my braces to look clean and almost finished. I will use 320 grit sandpaper .