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through notches cause weakness
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blues creek guitars Authorized Martin Repair Ctr

Total Topics: 52
Total Posts: 1011
A few asked me about this subject. I will try ans answer this so you can understand why.
A brace wether top or back should be notched to the kerfing and only into the kerfing. If you notch the side and set the braces through the guitar you do create a weak point. This is the point of the 2 corners of the notch. With the wood being well quartered you create a shear point by doing this.
Anytime you do a through cut and you have sharp corners you make a point where forces can focus and they can exert a force that can cause a failure.
If you ever seen a square hole in somthing you usually will see a crack develop at the corner , and the same is true with wood. The other problem you create is when you have the bracing through when you trim them and route the binding channel , it the braces splits or tears out you will have a nice split on the side to repair.
john hall

May 11, 07 | 5:03 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
That's interesting and it seems like you have had some bad experieinces -- Do you have any idea how Taylor or Larrviree are able to produce their instruments with through brace construction? Looking at the factory tour videos it can be seen thats the way they do it.

Ken

www.kennethmichaelguitars.com

May 11, 07 | 10:00 am
blues creek guitars Authorized Martin Repair Ctr

Total Topics: 52
Total Posts: 1011
I havn't had any as I can't see the value to this. it is not a better way just faster.to use through. I don't know any hand builders that use it.
john hall

May 12, 07 | 5:39 pm
john coste

Total Topics: 5
Total Posts: 51
Interesting, John...If I recall, metal fatigue around the square windows was a big problem of the De Havilland Comet, the first passenger jet airliner in the fifties. Enough planes crashed that it was grounded. Next time you fly take note that the windows all have rounded corners.

How do you cut and shape the braces and notches? Careful measurement and trial and error?

May 12, 07 | 6:31 pm
Herman

Total Topics: 38
Total Posts: 480
I'm with John here. In my kind of work (motorcyclemechanics) you see most of the time the fractures begin in the corners. For exemple a cranckshaft allways has to get radiused corners without burrs. Otherwise you'll find yourself one time in the middle of the desert with a broken cranckshaft.
It's a shame you got plenty of time then, when you don't have to search for the crack. It is where it allways is.

So in a guitar you should make the points of major stress as smooth as possible. No edges, no gaps, no square corners. Water and air and even sound do have to flow, so does force.
my 2 eurocents

May 13, 07 | 12:25 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
Gentlemen, this is a great conversation – however it would appear to me that we need to make sure we try and stay in the spirit of this forum in regard to sharing information and experience. Many in this group are new to the hobby and are looking for advice, and reassurance that they are on the right track. Sometimes it is difficult to separate facts, history, from opinion. Personally, I try to submit information that will ease the minds of the new builder and provide options and a variety proven successful methods of construction. I do not think its is fair to imply that those that choose to use such and such, or a widely used method or an other builders method, is on the road to building an inferior instrument.

Regarding this particular process I have personally have tried, chiseled out kerfing method, the chiseled out and step down method used by Cumpiano, the cut through and step down combination method used by Jim Williams the famous builder from Australia. And the cut through method used by Award winning Arthur Overholtzer, Taylor, and as John points out most Factories. Of all those methods, to me, the cut through is the easiest, requires least amount of skill and most often results in a perfect, attractive brace kerfing joint line with out kerfing damage. As attested by the fact that the factories, which provide lifetime warranties do not hesitate to use the cut through method, make it an easy assumption that structural failure after all those years of actual field-testing is not a concern. It is a time tested method, used on millions of guitars custom makers as well as countless factories and in my view is a good approach for the new comer on the road to building success. Bottom line, I think it’s important we do not mix the theoretical, with the facts. Or personal preferences and proven methods, and especially not to strike needless fears in the minds of the new builders. And as a final comment – if the 90 degree corner is of concern how about dragging a small rat tail file or folded piece of sand paper to relieve the intersection and also sanding a radius on the brace edge? I suppose this is way more than two cents – but building guitars needs to be fun and as stress free as possible. It is not necessary to do things the hard way to construct a fine instrument.

Ken

www.kennethmichaelguitars.com

May 13, 07 | 6:11 am
Bill Cory

Total Topics: 158
Total Posts: 3584
It seems to me that through notches should not be a problem at all. The corner of the notch is glued and sandwiched between glued kerfed lining and glued binding. That's three layers of reinforcement, counting the side itself, plus the glue's strength.

The guitar is a design built around fracture points, anyway. The soundhole is one, and is surrounded by braces and a rosette to strengthen it. The six holes in the top for the strings are six more, and they are immediately surrounded by the bridge and bridgeplate. The cut into the top for the dovetail or tenon usually has square edges, and it is surrounded by the neck, the fretboard extension and braces underneath.

Everywhere you find a fracture point, you find a lot of reinforcement surrounding it.

I see this as a non-issue; I cut through the sides because that's the way a lot of the people whose books I've read do it, and I don't think it's ever going to be a problem. It certainly doesn't have any effect whatsoever on the sound of the instrument, does it? -- but that's another argument from the Luthier's Corner about linking the top to the back.

I say just build them and enjoy them. If they break, build the next one differently.

Probably less than 2 cents.
Bill

May 13, 07 | 6:57 am
blues creek guitars Authorized Martin Repair Ctr

Total Topics: 52
Total Posts: 1011
Actually martin does not cut through the sides. I used a small dremel to inlet my kerfing and can inlet that in a few minutes but I agree I have done more than one set. As for through notching , I have seen alot of problems with this practice in repair work and do not recommmend any builder to use it.
If you use it and are happy with that , please don't change it on my account. Cupiano wrote his book in the 70's as did Williams. Alot has changed and as pointed out , in simple engineeing terms , stress will cause failures. This is the point I am trying to make in that through cutting adds stress points to the guitar that shouldn't be added.
Martin does this with the jig as you may have seen and they do not go through the sides at all. .
John hall

May 14, 07 | 5:42 pm
dcbaisden

Total Topics: 25
Total Posts: 58
John, What type of cutter bit do you use in the dremel,
thanks Dave

May 15, 07 | 5:24 am
blues creek guitars Authorized Martin Repair Ctr

Total Topics: 52
Total Posts: 1011
I use a 1/16 bit. I set it to 1/8 as that is my finish height of my braces on the ends and remove the kefing material.
john

May 15, 07 | 12:26 pm



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