Official Luthiers Forum!

Hi guys,
A couple of years ago I re-topped and restored a Gibson CF 100. The top I used was purchased from Herb David (original owner of Ann Arbor Guitars) It is German Spruce and was cut back in the 60s and I purchased 6 sets.

When I was choosing the wood from this stash I noticed they were quite floppy side to side but were very stiff with the grain but I was pretty committed to using it since it was almost as old as the guitar.
It went together well and when finished the guitar has a great sound. For the last couple of years I have been "sort of" abusing it and getting it to look "vintage", i.e. scratches, nicks, dings and dulling.

I noticed a couple of weeks ago that the top has started cracking below the bridge. They are not open cracks but more like splits in the grain. I am not bothered by them since I want the guitar to look 70+ years old.

Some things to note:
I keep my house humidity controlled and don't let it get under 40 or over 60, I own 17 guitars about half are acoustics so I keep humidity in check. This is the only guitar I have that has cracked and am wondering if this has to do with the floppy side to side top.

I am reluctant to use the other 5 tops if they are going to crack easily and would like to know what you think about side to side flex in tops.

Thanks for your help on this,

Cheers,
Bob

Herb David never owned Ann Arbor Guitars so again Bob if you don't know what the hell you are speaking of perhaps shut up? Please do not spread libelous lies about our business here or anywhere else.

I'm going to ask Lance to once again have to moderate your crap. Grow up man.

_________________
Ann Arbor Guitars

Hesh,

Please forgive me for confusing Herb David Studios/Luthier with Ann Arbor Guitars.

It may have had to do with the fact that you invited me down there to look at the wood I bought from Herb David. It was the exact building that Herb David made guitars which
at the time was called Ann Arbor Guitars. You told me all kinds of stories about Herb and all the famous people that stood exactly where I was standing... You even told me that you
bought the business from him and that is why he was selling off his wood.

So, You are going to site me for spreading "libelous lies" about you..

Tell me what I said that was libelous?

That I made the mistake that Herb David was connected to AAG? Is that a bad thing to say? You had tons of great things to say about him back then.

Is it because the wood I am talking about developed cracks? It was 60 year old wood! I didn't ask or expect a warranty... And I didn't buy the wood from AAG, I bought it from Herb David.

So please explain to me what I said that set you off.


My apologies Mr. Breakstone, I am sorry I offend you so much that you feel you have to try and berate me every time I try to post here. You seem to do this to people on this forum quite a bit.
I have been coming here for years now and am also a contributing member and it seem that most of the arguments and fights are started by you. So this seems typical of your behavior.

Not sure why you are so hostile to me.

I was just trying to ask a question about side stifness.

Unless all of you want to blacklist me over this, I would like to keep this on topic...

Thanks
Bob

Oh,, and by the way. Lance had NEVER moderated me or told me not to say or do anything here and YOU KNOW THAT...

IMHO, the low cross-grain stiffness and the cracks are unrelated. If anything, more cross-grain flexibility should reduce the chance of cracking.
Is the wood off-quarter? It only takes a degree or two off vertical to significanly affect cross-grain stiffness. That is because the cell structure of spruce is rectangular.

_________________
John

I don't think it has anything to do with top stiffness either. When you retopped it was your shop under good RH control? Did you build an outside mold to keep the shape of the guitar? Could be many things but probably not a well seasoned 60 year old top regardless of how stiff it is across the grain.

Since I have only built a couple of guitars and re-topped three guitars I repaired I don't have a lot of knowledge about this so thank you for helping. I sort-of had that idea that the floppy side stiffness wasn't a huge deal since I know woods like cedar have a fair amount of flex side to side but have never had a guitar develop cracks before.

As for being off quarter, I "self" graded these tops according to how well quarter sawn they were and this specific top was the best. The inside of the wood is almost dead on 90 degrees and skews off a few degrees but is not too far off of quarter. But I would say it is off by more than a degree or two.




Well that is encouraging that 2 answers tell me it isn't the side to side stifness.

I do keep my shop pretty close to 45% humidity most of the time. It may vary 5% either way but it is usually pretty stable. I especially watch it when I have something in progress.

Now one thing that is a big variable is that this is my only guitar I don't keep in a case. It lives in my office on a stand where I can grab it easily and play it. This is my main Go-To guitar and gets played at least once a day. I also keep it out of the case because I want it to get dusty so I can wipe it down with paper towel every once in a while. It has started developing a nice patina and is looking a bit worn now. The cracks do not bother me and I am sort-of glad since it just adds to the patina of the rest of the guitar.

wonder if just leaving it out on the stand allowed smaller humidity changes to occur where my others are all in cases where those small changes don't happen as much.

I am not too well versed in measuring and checking tonewoods but I do tap and flex the wood I have but really don't know what I am doing at this point. I figure if I listen to enough wood I will start to understand it.

I guess at this point it would be just speculation on why these cracks appeared but it sounds like it doesn't have to do with the side to side flex...

Thanks again,

Cheers
Bob

Hard to know what's going on without a picture. I have seen microfractures in many types of wood. Mahogany is probably the most common but spruce is up there too. Many times these fractures are caused by improper felling, like having the log hit another log or some other raised item on the forest floor. The log snaps across the fulcrum and microfractures can result. I've also seen these referred to as wind shakes. They can be very small and difficult to spot.

_________________
Stay with the happy people.
--Reynolds Large

A bit difficult to get a photo of but I did capture them.

The first shot shows where they are located and the others are close up. The first shows the wear I have put on it. Still not as "aged" as I want yet but it doesn't look new anymore

Cheers,
Bob

That looks like only the finish is cracked, since they don't follow the grain lines.

+1 what Dennis said. Nitro lacquer?

_________________
Stay with the happy people.
--Reynolds Large

Yes it is Lacquer. It is possible it could be just the lacquer but I am very well versed in spraying it and keep it quite thin. Not sure how many mils it is but I am betting it is thinner than most. It is also Behlen's instrument lacquer which is a bit more flexible.

Not saying it isn't just the lacquer but I have refinished 3 of my other guitars pretty much the same way and this is the only one to crack. Plus it has lived in my shop or my office since I restored it (no temp shocks or spikes).

I have been watching them for a couple of weeks now and they do not seem to be moving and I even put a bit of pressure on one of them to see if I could move it. There doesn't seem to be any movement so it could be possible they are just in the lacquer.

Thanks guys, I appreciate your input and suggestions,

Cheers,
Bob

The way the cracks cross the grain lines I agree they are finish cracks.

_________________
Steve Smith
"Music is what feelings sound like"

Mohawk went through a period of string instrument lacquer being very chippy and check prone. It happened around the time Seagrave went out of business.

_________________
Stay with the happy people.
--Reynolds Large

DennisK gets the door prize!

I took it down into my shop and under bright light and using my photographers loupe, I can see it is the finish, good catch!

What is odd is the edges of the cracks are curled up as if it's the wood.



I think this may be the culprit. Looking at some of the other distress marks I put on it they are all chipped and shattered with spider cracks. I have used Behlen for a number of years with no problems... until now. Now it makes me a bit nervous since I have repaired a number of different guitars that are out in the wild.

I guess this one will age a little quicker than I thought so I won't be so rough on it.

And you probably guessed from my avatar that the CF100 is one of my favorite guitars. FYI, This guitar is a 1950 (the first year made) but it is one of the first 300 guitars made. It was also the only cutaway acoustic that they made. (hence why I had to re-top it).

Thanks for the help,

Cheers,
Bob

I agree with others those look like finish cracks. You can test it with a bit of naptha to see if it comes through on the inside. But wow! That looks great. Really does look like a very old top on that guitar.

Thanks for the tip, Maybe put a bit of brown dye in that naptha to give them some "age"...
As for the look of the "aging" it has a bit to go before it matches the neck and back. But thank you, I do have to say that this guitar really sings and keeps getting better. Unlike most CF100's that sound a bit "boxy" this has a pretty good voice. In my mine it is because of the 60 year old top wood, but I guess that is all subjective.

OK, So I am confident what this issue is but...

I guess I took my own thread off topic

About side to side flex in tops.

Do you check it and what does it mean?

Cheers,
Bob

Cross stiffness in the top doesn't do much to reduce top deflection in the long run, IMO. It does have an effect on the tone, though. Mark Blanchard did some work on that, and basically decided that you should choose tops with high cross stiffness for guitars, such as Jumbos, that are wider relative to their length. 'Floppier' tops work fine on narrow shapes, such as the old Martin 1 parlor guitar.

Would you by chance know if that info by Mark is available, I didn't find anything searching but did find out he has a patent on a truss rod.

I did find this which talks about horizontal stiffness by Jim Blilie. He drops your name in the article so I am sure you know him.

A Large New Set of Stiffness Data for Lutherie Woods, and a Proposed Standard Test Method

https://www.barbarossa-guitars.com/misc/Articles/2017-01-13/Bending_Test_Article_25-Mar-2016.pdf

Interesting read, but unfortunately my interest isn't in numbers at this point. I am just trying get the basics figured out.



I would be interested in what you think.

It seems as most people don't worry too much about cross grain stiffness.

Cheers
Bob

So I took this guitar down in my shop for a full inspection and it appears that these are cracks in the wood... I applied naphtha to the outside and I could see that it came through on 2 of the cracks. What is odd is the cracks in the lacquer do not follow the grain lines in some spots. It almost looks as though the lacquer sheared on an angle. So not sure what that's about. (maybe a bad can of Behlin's as was mentioned earlier).

So I am getting ready to cleat them and call it good. As I said I don't really mind having the cracks since it adds to the "vibe" of an old top The guitar sounds great and I don't ever plan on selling it so I will just keep an eye on it..

I have tried to find more info on the internet about cross grain stiffness but there just doesn't seem to be much out there. The article I posted in my last post is about all I could find and that only talks briefly about it with a couple of small charts but it doesn't say what is good or bad.

One of the reasons I was curious about this is I am about to start building a 1830's Panormo and have one of these tops joined and ready to start thickness them. Since I don't have confidence in these old tops I am going to switch it out for one of the newer Sitka tops I have, but I am probably going to give these tops to the dumpster.

I will however keep trying to find info about cross grain stiffness because I think it may have something to do with the issue on this guitar.

Thanks for your help guys,

If anyone has any info or idea on this I am all ears...

Cheers,
Bob

I'm not sure I would be so quick to put them in the dumpster (unless the dumpster is code for mailing them to me). I get that you have doubts and are reluctant to use these tops, but I'm not sure you can equate what this top did to what the others will do simply because they came from the same place. Do you have reason to believe the other tops are cut from the same bolt as this one? I ask because the cracks may be a previous fault in the wood that no one would have ever been able to know about when selecting the top. It is hard to tell from the pictures but are the cracks both n the same spot of the bookmatch?

Others with way more experience than I have will be along to discuss this but I'd hold off on pitching them until they do.

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Bob,

I think that top would work great.
The small bodied Panormo would probably benefit from less cross-grain stiffnesss. If you string it up with nylons, like the Ambra 800's I have on a Stauffer copy, you have less than 90 pounds on the strings. Far less tension then on your steel string.

As far as cross grain stiffness goes. The little Electro-Less Paul 13 inch archtop I made has very terrible cross grain stiffness. (HD cedar, quartered in the middle, and fully 90 degrees on the sides) It has really good sound. Excellent bass, and tone, and resonance all over. I do have to fix a crack, but I wasn't thinking, and have the whole top in front of the upper bout OPEN! It is glued on the block; around the neck joint, and at the edges, but it is fully open where the humbucker would be. It started to crack right were the corner cut of the cutout for the humbucker is.
So it should be an easy fix. I will support it with something like a sound hole plate or bridge plate. I will see how much stiffer that makes it. I might put a 3/8" brass tube between the blocks to keep it from squishing in so easily. Who knows; I might even decide to add more tone bars for stiffness.The belly rises 5-6? mm with string tension.
But it really sounds great. The notes on the second octave up on the high E are not as strong, but they aren't lifeless.
I have 11-52 80/20 strings on it; so probably double what would be on a Panormo.

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Why be normal?

I've been sort of busy, which is why I didn't address your question earlier.

Mark Blanchard and I both use the 'tech' method of tap tone tuning by Chladni patterns. It's hard to justify in a strictly scientific sense (too many variables), but we (and some others) have found that it seems to work for us. The basic method is to build up a top with the bracing and check the resonant mode pitches and shapes using Chladni patterns. You then shave the braces to try to get the patterns to be 'right' as you understand it. This can be time consuming.

Mark got the idea some years back that it might be better to 'tune' the top before gluing on the braces. You could work on the thickness and graduations to establish some 'standard' set of patterns, and then simply glue on a standard set of bracing every time. This would take into account the fact that even 'identical' tops cut 'in flitch' from the same billet will be a bit different in detail, for any number of reasons. Mark spent quite a lot of time on this, and told me later that he wished he could get it back...

What he did find through checking the patterns on a lot of unbraced tops was that the ones that he liked better had certain features in common. These had to do with the way the standing wave patterns of the resonances form.

If you tap on a bar of wood a bending wave runs out both ways from the tapping point, reflects off the free ends, and runs back in, eventually bouncing off the other end, and so on. The initial tap contains energy at a lot of frequencies, but only the ones that make a round trip in the same time reinforce each other to produce an overall bending resonance. If you hold the (uniform rectangular) bar about 20% of the way in from either end, you can hear that pitch. You can also visualize it by supporting the bar at the two ends about 20% of the way in, sprinkling on some sawdust or glitter, and driving the bar at that pitch. The dust/glitter gathers on the non-moving 'node' lines.

Expand that bar outward in width to become a guitar top blank. In many cases you can see two such 'bar' bending modes at different frequencies, depending on how long it takes for the bending wave to make a round trip along and across the grain. If you draw the lines on the plate at each frequency you've got a tic-tac-toe board. But suppose that transit time is the same in both directions: what happens then?

In that case you might think the plate would do both things at the same time, and the pattern you'd see would be four dots where the lines cross at the original pitch. It's not that simple. The bending of the plate produces other forces, particularly from the 'Poisson's ratio' of the material, so that it no longer bends only along or across the grain to form the straight grid. Instead the lines curve, and you end up with two different patterns: an 'X' across the corners of the rectangle, and an 'O'. If the original bar bending mode was at 100 Hz, (say), the X could be at 97 Hz, and the O at 103, due to the Poisson's ratio.

Guitar tops are not rectangles, of course, but they do have families of modes at different pitches involving long and cross grain bending. Mark found three modes that seemed to tie in as quality markers. One is predominantly cross grain bending, one mostly long-grain, and one involves both. The latter two modes, one with a ring in the lower bout and a crosswise bar in the upper bout, and another that has a cross bar in the upper bout, and a line along the center line with a closed 'butterfly' in the lower bout, also show up on braced 'free' plates (not glued to the rim) and on assembled guitars. Getting these modes to form well, and in certain pitch relationships, seemed to produce 'better' guitars. Given what Mark gets for a guitar, and the reputation he has for good sound, it's hard to argue.

Those mode shapes on the unbraced plate are determined by the stiffness ratio of the wood, and the 'aspect ratio' of the outline. Most guitar bodies fall within a pretty narrow range of length, but the widths can vary a lot. What Mark does is to take all of his tops to the same thickness (heavy), and cut them to his largest outline. He looks at the modes, and, if they're 'right' he uses that top to make a guitar of that shape. If they're not right, they get trimmed down to the shape that works best for that wood. It's a matter of 'going with the flow' so to speak.

In particular: one indicator we've used for a long time is that 'ring-and-a half' mode on the braced top before gluing it to the rim: getting that to be active and well defined, with a 'closed' ring, has always seemed to give the best results. Mark found that if the unbraced plate won't give a 'closed' pattern, no amount of tinkering with the bracing will produce it. As he says: "The sound is in the top".

Hope this helps...

I like floppy tops for my small parlor guitars and would be happy to even pay you for those though it looks like Bryan has dibbs

But seriously put them in the classifieds and just sell them as floppy.

Or better yet keep them. I think what John said makes sense, a very stiff across the grain top might even be more prone to crack then a rubbery one.

If I decide to dump them I'll let you know, But after the advice from others I will probably hang on to them wile I see what comes of this Gibson.

As for being cut from the same log, I do believe they are. At Ann Arbor Guitar as it was called when I was there Herb David must have had hundreds of them on shelves up out of the way. All the tops I bought were numberd in the 600's. They all look similar in color and grain so I would say yes they are consecutive

The cracks are not in the exact same grain lines but are close. They are about 1/4" from being symmetrical. But it is possible they are a fault in the log.




You are right, Thinking about just doing it and once the top is cut to the general shape see how it is. As for cracks,,, Again, I have no problem with that since I am planning on making a "replica" so it will be aged and appear original.



Yea, thats probably what I am going to do, I'm going to inspect the others to see if the have any visible cracks using naphtha.




No problem Allan,
I have seen info on your work with Chladni patterns but have not really looked into it very deep. I am a very visual person and understand things better if I can see it.
I thought I saved a bookmark on it but can't seem to find it but I will be looking more into this.

Does your DVD cover this?

Thanks for your help

And thanks for all of your input guys.

Cheers,
Bob

It's quite possible that when the crack happened in the wood it also cracked the finish which followed the grain line but since it has no real structure wandered a bit.