Acoustic Guitar Construction in the small shop -- Kenneth Michael Guitars LLC

Information, ideas and help for those constructing scratch built acoustic guitars or acoustic guitar kits - © 2017
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The purpose of this forum site is to provide a means for acoustic guitar makers at all skill levels to forward information, share experience and ask questions if project obstacles are encountered. We ask that egos be left at the door – the highest levels of courtesy and respect are to be shown to all. Posts containing disparaging comments will be removed. The “Acoustic Guitar Construction Forum” is owned by Kenneth Michael Guitars and is copy protected. Direct links to luthier suppliers are not permitted and will be edited.



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 Post subject: Little help please.
PostPosted: Tue Nov 28, 2017 5:53 pm 
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At the following link, the top post is by JOhn How, and he gives specs for his ladder-braced guitars.
There are also images that I can't open!!

Could you give the link a try and see if you can get the images and copy them for me - maybe post them here?

Thanks

http://www.luthiersforum.com/forum/view ... la#p225388

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 Post subject: Re: Little help please.
PostPosted: Tue Nov 28, 2017 6:44 pm 
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Location: Seattle
Unfortunately John How does not have the images on website anymore. The site at www.johnhowguitars.com is a minimally done word press site with nothing about guitar building.

Here is one of the links from the post you had a link for.

http://www.johnhowguitars.com/images/Misc/LBC_Pattern_Top.jpg

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 Post subject: Re: Little help please.
PostPosted: Tue Nov 28, 2017 6:46 pm 
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Okay, thank you John.

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 Post subject: Re: Little help please.
PostPosted: Fri Dec 01, 2017 3:56 pm 
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Dave,

When John How operated his web site, I downloaded one of the images of a LB top after it was finished and signed. I could not find it, but had sent a copy to Will Reyer, who kindly sent it back yesterday. It illustrates just how simply How manages the question of potato chipping with three logically spaced braces and a bridge pad. This is exactly how the 100 year old Oscar Schmidt I am restoring handled it, and that top has not potato-chipped, despite being strung up with steel strings (.051 - .010).

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File comment: John How top, 2010
ladderbraced.jpg
ladderbraced.jpg [ 124.38 KiB | Viewed 141 times ]

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 Post subject: Re: Little help please.
PostPosted: Fri Dec 01, 2017 4:18 pm 
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A theoretical comment:

LB guitars have a well deserved reputation for producing a "cutting" sound and in some cases, having a loud voice as well. Somogyi points out reasons the approach tends to emphasize treble, which is part of how they achieve their voice. The ladder braces create fulcrum points that release the top to vibrate for a short distance in the long pole, but inhibit movement in the cross pole. I would like to point out that the more braces that are used, the more likely treble will be emphasized because treble is best generated by short spans of vibrating wood - short amplitude, in other words.

Harmony 1260s, for instance, use five braces and despite their larger box, do not produce the growler type bass my much smaller Oscar Schmidt gives me. Leaving out T3 and perhaps T4 or T5 might give the 1260 a lot richer bass, assuming the top was stiff enough to resist potato-chipping. (The 1260 I deconstructed for this photo had a very floppy top.)

I think there is a lot to be said for using as few braces as possible, with spacing that affords at least one long amplitude expanse of top to vibrate at a lower natural frequency, which is one way to explain why John How gets well balanced results in his instruments. I'm assuming he is quite choosy about the wood he uses for tops.

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File comment: Harmony 1260 bracing
Harmony 1260 top.jpg
Harmony 1260 top.jpg [ 71.72 KiB | Viewed 139 times ]

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 Post subject: Re: Little help please.
PostPosted: Fri Dec 01, 2017 5:06 pm 
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Thanks John, I found this very interesting.

I'm part way into a new project, and just decided to go with LB ala How. The one thing that has me toying with the idea of a 4th brace is a comment by John Arnold, no stranger to LB guitars, who stated that the best ones always had one brace angled from about the waist area towards the 'treble' side. Then again, were they better sounding than How?

Question - from what I have seen of the innards of a few Hows, the bridge plate is NOT inset into the large spruce piece, but is glued ON TOP. Is that the way it looks to you?

Here's a pic - not a How - to illustrate the angled brace; it would become the new third brace, and the old third brace would be eliminated. Also, the A-framed upper bout makes sense to me. What thinkest thou?


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 Post subject: Re: Little help please.
PostPosted: Sat Dec 02, 2017 2:06 am 
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Dave, I have a 100+ year old Brazilian parlor guitar that I am almost finished with that uses that Z-diagonal brace you are considering. It is almost to the point of stringing up, but not quite. I am curious how it will sound and wish I could report on that.

The top is spruce and extremely thin, so I may use nylon strings on it, even though it has a pin type bridge. Thus, it might be worthless as a predictor of what you are contemplating, which I assume is steel stringed. I understand the Z-brace was common during that time.

As far as the A brace goes it could be a solution to potato-chipping. A variation on the A brace might be to use a tall but thin brace at #2, then lap joint the legs of the A into it at the top, using the fact stiffness increases by the cube of the extra height, and would greatly stabilize the top half of the instrument, which supposedly does not vibrate much anyway. If the legs were that tall, there might not be a need for #1 or the Z-brace.

Or you could gradate the thickness of the top, thinning once you get past the sound hole. As you know Maccaferri tops are complexly gradated. But they are also populated by many braces, which just does not allow the growly bass that interests me. Lots of cut, though.

In any case, I lean away from gluing the long bridge pad smack up against a brace, which would then form an L beam that probably limits motion more than when the two parts are separated. (John P might have something more definitive to say about that than I do.) The way both How and Harmony float the bridge pad seems like it leaves more room for the top to move.

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 Post subject: Re: Little help please.
PostPosted: Sat Dec 02, 2017 2:40 am 
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John - thanks again. I am going to use the upper-bout A frame, and let the apex of the A into the headblock. I've been doing that on the last several instruments.

Agreed that the long bridge pad should 'float' above that bottom brace - I'll be following How's pattern fairly closely, and he does the float, with the bridge plate not inlaid, but glued on top of the pad, unlike most of the others I've seen. He also says to use the stiffest spruce I have for that pad, and to make sure the grain is vertical. Makes sense.

Don't think I will take any complicated approach to geometry of the top - around .110" for the bearclaw Sitka, with some perimeter thinning. How's braces look pretty substantial, at least 5/16" wide and looks like almost 3/4" tall. Some of those specs feel a little off to me, due to the fact that x-bracing calls for a different approach. I'll start off with braces to his specs and see how responsive the top feels. I've got to assume that we still want a responsive guitar, albeit ladder-braced.

Dave

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 Post subject: Re: Little help please.
PostPosted: Sat Dec 02, 2017 7:48 pm 
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Forgot to mention: My 1920s Oscar Schmidt floats the bridge plate on top of the bridge pad.

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 Post subject: Re: Little help please.
PostPosted: Sat Dec 02, 2017 8:51 pm 
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Aha. I'm not certain there are any (dis)advantages either way, but How seems to have a good system.

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