Official Luthiers Forum!

Glad to see everyone had a great time at ASIA, I wish I could have been there. What a pity it was ten thousand miles away

Now, can somebody please put me out of my misery and explain what was going on with the sugar cubes?

Cheers,

Paul

Ervin was showing an example if the cubed strength of a brace, and how much stronger it was where there were just a small amount more wood. Each cube represented a set amount. Its a little over my head, glad I got it all on digital video

_________________
Support the OLF! Bookmark our STEWMAC link Today!
Lance@LuthiersForum.com

Ervin was visually demonstrating the strength of a brace by showing what it would look like if you could see how much strength there was in each brace. He had Judy Threet come up and do this while we took a break. Ervin was saying that the brace gets exponentially stronger as it goes up. I can't remember the number off the top of my head, but somewhere between 5 and 8 times more for every 1/8th of an inch. Maybe someone out there can explain better.

Judy also mentioned that the little patch that we put over the top of the X brace lap joint only needs to be 1/16th of an inch thick, as this is just as strong as it needs to be. This is based on much study of strength that she had done.
Tracy

A note for clarification: The brace gets much stronger as it gets TALLER--not so much as it get wider!

Carlton

It is a function of the cube, so a brace 1 unit high would have a strength of 1.

A brace 2 units high would have a strength of 8 times stronger.

3 units high would be 27 times stronger.

The point was that braces are exponentially stronger the taller they get and a "little" wood makes a huge difference.

He also had some interesting revelations about the lap joint in the x-brace.

Unless I totally missed it, he said that unless you cap the x-brace the brace is only as strong as the height of the lap..... not the full height of the x brace regardless of the fact that you "filled" the void with the other brace.

I was capping the lap joint anyway, but that was somewhat of a revelation to me.


I really think Ervin's 7 day class (the expanded version of that seminar) looks like money and time very well spent.

I got a lot out of that seminar.




:-)

Brock Poling38523.877037037

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Guess I will start putting a cap on my x-brace.

I guess next time I really need to go myself.

Josh

_________________
Josh House

Canadian Luthier Supply
http://www.canadianluthiersupply.com
https://www.facebook.com/canadianluthiersupply?ref=hl
House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

Unless I totally missed it, he said that unless you cap the x-brace the brace is only as strong as the height of the lap..... not the full height of the x brace regardless of the fact that you "filled" the void with the other brace.

This is an interesting concept but it just doesn't hold water for me. I've always capped my X's (all four of them on my tops) simply because each one has an end grain to cross grain joint. Very week. But I have troubles believing that the joint would not add ANYTHING to the strength of the brace. Brock, can you expand any on what he was saying or am I going to have to shell out $2500 and go to his class?javascript:AddSmileyIcon('')

Paul, they were saying that when you notch the x brace, the brace that is top notched is only as strong as the wood in the notch and since it is just end glued to the other brace there is really not much strength there. What Judy said was that it only takes a patch 1/16" tall to restore the strength to what it was when the brace was full hieght.

The unit value in the sugar cube demo applies to a unit that has dimensions equal to the thickness or width of your brace.

What he was trying to demonstrate (I think) is that most people over brace their tops. He spoke to great extent about not building a guitar stronger or heavier than it takes to hold it together and produce the desired tone.

_________________
Tickle your guitar daily, and it'll tickle you back.

[QUOTE=Brock Poling] It is a function of the cube, so a brace 1 unit high would have a strength of 1.

A brace 2 units high would have a strength of 8 times stronger.

3 units high would be 27 times stronger.

The point was that braces are exponentially stronger the taller they get and a "little" wood makes a huge difference.[/QUOTE]

I thought that's what he might have been talking about. Did he mention anything about finding the optimum brace height?

[QUOTE=Brock Poling]
He also had some interesting revelations about the lap joint in the x-brace.

Unless I totally missed it, he said that unless you cap the x-brace the brace is only as strong as the height of the lap..... not the full height of the x brace regardless of the fact that you "filled" the void with the other brace.

I was capping the lap joint anyway, but that was somewhat of a revelation to me.

[/QUOTE]

It makes sense though, if you put a lap joint in an "I" beam, you'd expect it to be weaker unless you put a cap on it.

I think I might get me a copy of that DVD when ASIA start selling them.

Thanks guys.

Has Judy or Ervin published the results of thier studies anywhere? Sounds like interesting stuff.

Don't think so Paul. You will have to take Ervin's 7 day class to get all the details. As for Judy's info, we'll probably find it published at some point, but not yet.
Tracy

[QUOTE=PaulB] Thanks guys.

Has Judy or Ervin published the results of thier studies anywhere? Sounds like interesting stuff.[/QUOTE]
The topics in this thread are covered in sophomore level engineering classes. There are enough engineers here we can sort this out.

As far as the cap on the x-braces, it's probably a good idea for long-term life of the instrument. The glue of an unsupported joint is not going to last forever. And it's true that at that distance from the soundboard a fairly thin cap will restore the full strength of the brace.

Yeah they were saying that a cap as thin as 1/64" of an inch restored the full strength of the brace.

Honestly I don't think we can sort this out... engineering or not. I will be the first to point out that I think there are some VERY smart people on this forum... but it was extremely evident that Ervin has been thinking about this one specific problem for decades and has come up with a method of tuning a top.

The cube of the height example was simply ground work that he laid before starting to explain the bracing and tuning idea.

I think to fully understand his approach you would need to take his class and come home and try to apply what you learned in your shop.

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com

One thing he didn't mention was that based on the I-beam concept you don't need to keep the width of the beam/brace all the way to the top for it to keep it's strength. If you noticed his braces on the test model were tall and they thined toward the tops.

I highly recommend his class. The man is in a whole different league when it comes to Luthiery. Four hours with Ervin was/is a real eye opener...7 days will change your life.

_________________
Dave Bland

remember...

"If it doesn't play in tune...it's just pretty wood"

I didn't say we could solve the top tuning problem, but the stiffness of a brace is a reasonably straightforward engineering problem. As are the issues involved in capping the x-brace. Those were the only two aspects of his talk that had been discussed in this thread when I posted my comment. To be clear, analyzing the dynamics of a guitar top would not be a trivial excercise, not to mention a complete guitar. There is one Ph.D. thesis about this online, and a few more recent ones that as far as I can tell are not online. I've resolved to start reading the one I downloaded.

I'm very interested in what Ervin had to say about tuning, It's the main thing I wanted to go to ASIA for, too bad I couldn't make it.

Sorry if you thought I was being critical... I wasn't. My only point was this was background info before he started getting into the meat of his talk.

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com