x brace not seated on new build

[buzzsawlouie]

Hi Everyone!

I just finished gluing the braces to my top and when I started to work on shaping the braced 1 noticed that one of the x-braces was lifter to one side so the is a gap on one side of the brace. Using a feeler gage the gap extends under the brace for about 1/8 inch, mostly right at the X. Here is a pic to illustrate:



On the other side of the brace it looks to be fine:




So question is, and I think I know the answer, do I remove the brace and try again with a new brace?? I assume I would need to make sure I remove ALL of the brace and glue residue so new brace would get good wood to wood contact..

Thoughts.?

Thanks Mark

[runamuck]

Yeah, you know the answer. Sorry.

[TheGITM]

You didn't really ask, but I think your issue may have been this... looks like the cut was just a tad too narrow to sit flush. The other side looks good.

Always dry fit everything... several times, even... just to be sure everything is flush and well-fitted before gluing...

Good thing you caught it now.

[Howard Klepper]

I recommend that you remove both arms of the X and learn how to make a full lap joint before replacing them.

[nikpearson]

Originally Posted by Howard Klepper

I recommend that you remove both arms of the X and learn how to make a full lap joint before replacing them.

The overlap certainly needs to be well-fitting, but not too tight to stop the arms seating fully. Dry fitting everything before final gluing is critical.

How do you make an X-brace with a full lap joint? I’ve always done this by cutting a notch in the two braces - perhaps best described as a cross lap- leaving the resulting cross point the full thickness of one brace. I thought a full lap was where no material is removed and the pieces of wood are just screwed or nailed together.

My technical knowledge of woodwork terms is patchy at best, so feel free to correct me.

[buzzsawlouie]

thanks everyone for your opinions! I did dry fit the joint and it did appear to fit nice and snugly. I had a lot of glue squeeze out so I assumed I was good there. I neglected to focus on the brace sitting flat on the top. I assume when sanding the brace I didn't sand the bottom perfectly flat.

Will have to chalk this up to a hard lesson in lutherie. Certainly not the first lesson, pretty sure won't be the last!! In my opinion what make this fun!!

[phavriluk]

I think Louie has done himself a big favor by posting those very nicely done photos - - - half of that x-brace is useless, the half with the wood scooped away in the middle. I'm sure there are lots of photos available on the web that illustrate valid techniques.

And I concur with other advice about the need for tightly-fitted wood-to-wood joints.

[buzzsawlouie]

Why do you say the "scooped out" brace is useless?? I am following the plans that suggest the x-brace is scalloped that way.



This will be my 5th acoustic build all using the same scalloping and each guitar sounds fine (actually not bragging but my last one REALLY sounds good ;-). I have researched and seen other methods but this one seems to work. What am I missing??

[nikpearson]

The scoop in the middle of the X will reduce stiffness in the is area by a very significant amount. The stiffness of a beam is proportional to the cube of its height, so removing just a little height can be dramatic.

String tension will rotate the bridge forward towards the sound-hole, the weakest part of the top, and the bracing pattern you’ve used means this area is much less stiff than is common. You could even say it defeats the purpose of an X-brace.

Building a responsive instrument is a balancing act. Too much stiffness and it will sound dead, too little and the instrument won’t be stable over time.

There are luthiers with much, much more experience than me on this forum, but in my experience the area where the x-braces intersect need to be full height.

[TheGITM]

I'll just add that the choice on whether or not to scoop from the intersection on the x brace should not be based on a generic design, but rather, it should be based on the desire to get a certain soundboard response. In other words, you should determine where to shave braces based on that specific guitar top and resonant response you get when tap-tuning. No two tops will be alike. They may be similar, but each top is unique.

In general, removing brace material is going to allow more up/down vibrational movement in the top which will favor a deeper bass response. Done well, you can create a very well-balanced and clear spectrum of tones. Done poorly, you can create a lot of muddiness and inadvertently suppress some of the tonal spectrum.

How do you know how to tune a guitar top? That's the million dollar question.

For this specific guitar, I get that the design calls for this section of the x brace to be scooped. It may be fine, I really can't say, but if you compare across a variety of guitar designs you will see that this is the exception. Most standard designs have a full height x brace intersect, but are often scoops elsewhere in the bracing, often to either side of the x brace insect point.

There are other choices that can be made as far as the size of the bracing, the width, the height, etc. But all of those choices are for the purpose of getting the best possible response from the top. In reality, no cookie-cutter design is going to be optimal. They will get you most of the way there, but the optimal result will only come from the builder working with the specific top to tune it for the best possible response... based on the goals of the builder for that specific guitar.

As previously mentioned, this specific area of the guitar absorbs a lot of forces so anything that weakens that area should be a very intentional decision. There are trade-offs between improving responsiveness and weakening the structure. I would think that this design would make more sense on short-scale guitars, or guitars intended for light strings only, or guitars that are intended to be tuned down half step or more. I would be cautious doing this on a full scale dread with medium strings.

But that's just me, and I'm not an expert, despite my penchant for sleeping at many Holiday Inn Expresses over the years. I just think I'm an expert.

Good luck with the build! Enjoy the process, and for goodness sakes clean up those shaved areas... they should be clean and smooth...

Happy Thursday!

[IndianHillMike]

Every guitar I've built in the past 15 years has a scooped x-brace joint similar to that -- probably not as extreme but it's hard to tell from the photo. I see no problem doing it that way and have never had any issues or seen any detrimental effects down the line. Sergei de Jonge (whom I apprenticed under) does all of his x-braces with one leg being lower at the intersection -- he's built A LOT of guitars that way and has had many many students do the same. One benefit of doing it this way is that with no risk of the joint opening up, you don't need to cover the top with cloth or glue another piece of wood to tie it all together.

[buzzsawlouie]

Thank you everyone for your input!! Thats what's makes forums like this great, getting different perspectives. As I mentioned before this is my 5th build so by no stretch of any imagination do I consider myself proficient in any of this. All these view points are extremely helpful to this young builder. Here are the plans that point this out, and it does state that it weakens the joint but will result in a better sound which has always been the goal, to get the best sound possible. But point well taken that may not be prudent to use this as a standard approach...



I will have to try my next build without the scallop at the brace to see if I can tell a difference.

@TheGIYM.. yes those braces will get cleaned up. I was just starting to shape the braces when I discovered the original issue..