tone of back

[rstbkt]

I was able to attach the two lower braces on the back yesterday. Have not taken the time to assemble a go-bar deck of some sort and I don't have enough clamps with a reach long enough to reach into the center of all 4 braces. And i have yet to acquire a radius dish but I do have two ribs with the radius cut into them. i used the ribs with sandpaper attached to radius the braces and then used the ribs placed under the location of the braces to shape the back as the braces were installed. When I was acting like I knew what I was doing and tapped the back after the glue dried I was surprised to hear a very mellow and low tone spring out of the back with an unusually long sustain for just being tapped. I was pleasantly surprised. I will attach the two upper braces tonight. Will the thinner upper braces remove the mellowness from the tone that I get now? I suspect ( first build so don't know diddly squat) that the pitch of the note will be pulled up and the sustain will diminsh?

[Darryl Young]

I doubt anyone can answer your question with certainity. You need the upper braces so it's likely a moot point. After these are glued in place you can shape the braces to adjust (or tune) the tone produced.

About the tapping, the tone of the tap and sustain, etc. will change depending on where you are holding/supporting the back when tapped. Usually the back is held with one hand and tapped with the other. Depending on which vibration mode you want to excite, where you want to hold the top/back matters.

My suggestion is to tap all the time......listen to how the tone and sustain change after each step and you will start learning. Also, flex the plate before and after each operation and see where stiffness is added and how much stiffness.

I don't think anyone has this completely figured out so you will just join everyone else trying to figure out the process.

I'd suggest that your next step be acquisition of that radius dish. The back will need radiusing in not only side to side but also in front to back. Keep this in mind before you radius any other braces.
A great source for basic info on 'tuning' backs and tops can be found in Robbie O'Brien's acoustic guitar tutorial. Robbie does not claim to have come up with the end-all solution but he does demonstrate and explain the process which "works for him."

http://www.obrienguitars.com/courses/ac/

-tommy

[rstbkt]

In one of my other questions/posts I had asked about the use of a radius dish and a a body shaped..........mold I guess....that I had seen on several tutorials. I was under the impression that these body shaped molds used for glueing in brace was not radiused like a dish but more like radiused on a plane. Or if that termonology is wrong just a curve running from top to bottom. Is this not the case? I will be cutting out my dish this weekend. i have a cnc router that I just completed the build on a couple of weeks ago but my copy of the control software is just a demo version. And I need to build the piggy bank up a little more before I spring for the 175 dollar cost But I know enough code to get me in trouble and will be hogging out the dish with many many manual inputs. But i digress, I can see on the top where you have many differnt functions with different braces and having them moving many directions that a dish is needed. but I cant see where that would come into play on the back where they are only running in one direction. Tommy, I'm not trying to argue the point, I just want to gain more information so I can build properly

http://www.youtube.com/watch?v=ismWy-GFvEk

[rienk]

II can see on the top where you have many differnt functions with different braces and having them moving many directions that a dish is needed. but I cant see where that would come into play on the back where they are only running in one direction. Tommy, I'm not trying to argue the point, I just want to gain more information so I can build properly

I think you may be misuderstanding; the back IS a complex curve. In other words, it is not simply a section of a cylinder with a curve in one direction - it is a section of a sphere, with curves on all axis. Thus, you really need the radius dish to not only glue down your bracing, but it also comes in handy to get the true spherical edge on the gluing face of the braces (as shown in Robbie's video).

The problem with using a radius dish to contour the top is in needing a flat spot for the fretboard to glue down to. This requires a bit of geometry and hybrid curvatures (as is mentioned on several of John's videos). I'm still not sure I understand how they go about getting that perfect, but that is definitely something you should grasp (it doesn't matter for my guitars, because I am building with cantilevered necks).

[tippie53]

The top has some complex geometry but that isn't that hard once you grasp the most important part is that angle. Get the neck angle right you are golden
What the dish does , it allows you control so you can be precise in your adjustment. As you work the dish you are sanding the sides and you are watching the symmetry of the chalk marker. You can see that the left and right side are similar. Once you have removed the chalk to the point of the top of the sound hole you then flatten the curvature at the fretboard extension.
I look for about a 3/8 inch gap at the tail block with the flat side of the dish on the ramp. What we want is to create a reasonably flat angle rise on the top. Once the guitar is built , you can tweak this if you wish . I do want to see the fret board straight but will allow a .020 fall on the extension from the 14th to the 20th fret.
You don't want a rise in this area.

[rstbkt]

Thanks everyone. I carved out my radius dishes this weekend. i was never going to add the braces to the front without one. didn't see the need for a radius dish for the back at the time but I did use some radiused ribs placed behind the back when the braces were glued in. the braces were radiused and when placed on the back and clamped in the braces forced the back to conform the the radiused ribs. So do I need to remove the back braces and start over? Hope not because I used tite bond on those instead of white glue. Like I said on the front with the braces running in many directions I see the need for the radius dish. but with the back braces running parallel to one another it seems like I have achieved the same thing.The back has a radius. Please don't let my need for an explination come across as being argumentative. Just trying to see where I can improve. ok I can improve everything i do because its my first build. LOL I guess we don't have to take this any further because I have the dishes now. I understand that had the back been in a dish that the top and bottom would in a way be radiused in all directions making it take on the shape of the dish. But since there is nothing in the verticle holding the back to the radius as there is on the horizontal what is the difference from just radiusing in one direction.

So do I need to remove the back braces and start over? Hope not because I used tite bond on those instead of white glue.

I justified the removal of the improperly radiused back braces and application of properly radiused back braces on my first (still in progress) by telling myself it would eliminate one possible reason if the finished product sounded lousy.
Someone referred to do-overs as building your first guitar twice.
-tommy

[rienk]

Someone referred to do-overs as building your first guitar twice.
-tommy

I fully intend to build quite a number of my "first" guitar... no one will be the wiser

,,, unless our guitars become famous after I'm long gone - and then the super rich collectors of my guitars can fight over who "really" has the first one. LOL

Or maybe my first guitar will be the first one I complete successfully that sounds and looks good... everything prior to that is getting some other headplate. (in that case, I hope I actually HAVE a first guitar)