Official Luthiers Forum!
http://mowrystrings.luthiersforum.com/forum/

first top failure not the joint
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=14287		 Page 1 of 1
Author:  Michael Dale Payne [ Mon Oct 29, 2007 9:20 am ]
Post subject: 
Sorry guys My camera is out of town but I thought I would run this one by you anyway

I was rubbing out the finish on a Sitka Bear clawed top this weekend and as I was sanding the top started developing cracks in the wood, not the finish though I would assume they would cause problems in the finish sooner or later. Anyway the cracks are from 1" to 3" long. One each side of the neck block from about 3" long asnd 1" from the binding runing towards the sound hole. (with the grain of corce in fact right on a ring line) The weird thing is the top is .110" thick in the area of the cracks and the cracks are almost mirror images of each other. Very little of any separation. Also one 1" long, 3" below the sound hole on the treble side.

I have never seen this and I was not leaning on the top or putting any abnormal stress on it. All three appeared almost simultaneously.

This top worries me so I am going to replace it.

The only thing that really ticks me is I will have to rebuild the rosette (maybe) and the abalone edge purfling (no way to save it really worth the effort)

I have never seen anything like it before. I checked the thickness with caliper and all is fine.

First though that came to my mind was if my RH in the shop had dramatically dropped but it is and has been the same with in 5% or less since the box was closed.

It is just strange.
Author:  Pwoolson [ Mon Oct 29, 2007 9:36 am ]
Post subject: 
Since the cracks are bookmatched, my guess is that they were there before you build it. Maybe they were smaller and you couldn't see them.
Author:  Claire [ Mon Oct 29, 2007 10:15 am ]
Post subject: 
Hi Michael.
I'm wondering if there were blind internal fractures or check marks in the wood.
Are the cracks apparent through the full thickness of timber? or just on the outside part that you can see?

I'm just guessintg here, however:
When you sand it also creates friction heat, and perhaps the finish you're using has more elasticity, and expands and contracts at a different rate to the timber underneath.

Good luck.

Cheers,
Claire

Author:  Don Williams [ Mon Oct 29, 2007 10:18 am ]
Post subject: 
I'm wondering if you left the neck block a tad too high, causing the fractures... that happened to me on a back before.
Author:  Terry Stowell [ Mon Oct 29, 2007 10:21 am ]
Post subject: 

Stress cracks from when the tree was felled?

Author:  Bruce Dickey [ Mon Oct 29, 2007 10:50 am ]
Post subject: 
Sorry about that Michael, that's no fun. Glad you see the wisdom in just calling it now and replacing it. You'll be glad you did I'm sure. Thanks for sharing, it proves that experience is important.

I wonder if it could have been spotted in a flexing exercise looking for just such a defect? First time I've heard of it.
Author:  Bruce Dickey [ Mon Oct 29, 2007 10:56 am ]
Post subject: 
How seasoned was this top Michael?

I reread the post and see it's near the neck block.

I'm not sure but there were some older major brand guitars that cracked along the fretboard edge on both sides. It's as if the top wood shrank away from a very secured area of the top?

(Watching this thread)
Author:  Bobc [ Mon Oct 29, 2007 11:34 am ]
Post subject: 
Well I'll offer a combo of Paul and Don's suggestions.
Book matched cracks on either side of the neck block suggests a neck block that was a tad high.
Author:  Dave-SKG [ Mon Oct 29, 2007 12:05 pm ]
Post subject: 

[QUOTE=Bobc]Well I'll offer a combo of Paul and Don's suggestions.
Book matched cracks on either side of the neck block suggests a neck block that was a tad high. [/QUOTE]


I'm with goomps (bobc) on this one...the fact that the cracks are "bookmatched" just means the top was...well...bookmatched. It definitely appears to be from the block being at the wrong angle and or a tad too high. With equal pressure on each side the cracks gave way to the pressure in similar "book matched" locations.
Author:  BruceH [ Mon Oct 29, 2007 12:22 pm ]
Post subject: 
I have a guitar with the same problem. My bookmatched cracks are about 3" long and halfway between the soundhole and the side. I fret with the neck off of the guitar. This is a cedar top about .125 thick with a thin fp finish. Although they look like cracks, they don't act like it. I can't get any movement when I press around them.
Author:  Bruce Dickey [ Mon Oct 29, 2007 1:26 pm ]
Post subject: 
Pics Guys. TIA

Bruce, how aged was your top?Bruce Dickey39384.8944097222
Author:  WaddyThomson [ Mon Oct 29, 2007 1:30 pm ]
Post subject: 

[QUOTE=Bruce Dickey]Edited by Bruce Dickey on October 29 2007 at 9:27pm[/QUOTE]

Unh Huh!  See!
Author:  BruceH [ Tue Oct 30, 2007 3:26 am ]
Post subject: 
[QUOTE=Bruce Dickey] Pics Guys. TIA

Bruce, how aged was your top?[/QUOTE]

I'm not really sure. This was a piece from the group buy offered by Jason here a couple of years ago.

Edited by BruceH on 30 October 2007 at 11:18pm
Author:  Michael Dale Payne [ Tue Oct 30, 2007 3:51 am ]
Post subject: 
[QUOTE=Don Williams] I'm wondering if you left the neck block a tad too high, causing the fractures... that happened to me on a back before.[/QUOTE]

Bowl sanded so I don't see how
Author:  Michael Dale Payne [ Tue Oct 30, 2007 3:53 am ]
Post subject: 
[QUOTE=Bruce Dickey] How seasoned was this top Michael?

I reread the post and see it's near the neck block.

I'm not sure but there were some older major brand guitars that cracked along the fretboard edge on both sides. It's as if the top wood shrank away from a very secured area of the top?

(Watching this thread)[/QUOTE]

i have had the top for a year and it was 11%mc when I got it and 9% when I braced it
Author:  Michael Dale Payne [ Tue Oct 30, 2007 3:54 am ]
Post subject: 
[QUOTE=Hesh1956] Paul's point about the cracks being booked match is a great point.

Did you install the frets the with the neck installed and perhaps the backing block used for the extension didn't take the blows well enough.[/QUOTE]

Neck was not installed as of yet I fret after final neck installation so no
Author:  grumpy [ Tue Oct 30, 2007 4:17 am ]
Post subject: 
Wood sometimes does this, without provocation or reason. Could be an internal stress that relieved itself, could simply be a check or hairline crack that you didn't see until you began fine sanding.

Go ahead and try to find a cause, study the neck block, look back on the RH of the past few weeks, but in the end, if you don't find a reason, just accept it, rip the top off and start over. It happens.
Author:  burbank [ Tue Oct 30, 2007 4:30 am ]
Post subject: 
Upper transverse brace not radiused?
Author:  burbank [ Tue Oct 30, 2007 4:32 am ]
Post subject: 
Never mind.


[QUOTE=MichaelP]......from the binding runing towards the sound hole......[/QUOTE]
Author:  Dave White [ Tue Oct 30, 2007 4:51 am ]
Post subject: 
Michael,

It's at times like this that I remember Charles Hoffman's wonderful quote:

“It has been exhaustively demonstrated that under rigorously controlled conditions carefully selected pieces of wood will do pretty much what they dang well please.”

I suspect that Mario is probably correct in his diagnosis.
Author:  Bill Greene [ Tue Oct 30, 2007 5:04 am ]
Post subject: 
[QUOTE=Dave White] Michael,

It's at times like this that I remember Charles Hoffman's wonderful quote:

“It has been exhaustively demonstrated that under rigorously controlled conditions carefully selected pieces of wood will do pretty much what they dang well please.”

I suspect that Mario is probably correct in his diagnosis.
[/QUOTE]

That's sensational. Love that quote.
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/