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  #1  
Old 01-08-2022, 08:40 AM
sgabalski sgabalski is offline
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Default Tops cracked at neck block!!!

Ok I am building three at one time. my 2nd, 3rd and 4th. Everything was going ok. I am about to bind them and noticed all three have a crack on the top running on the edges of the heal block, from the top toward the sound hole. I would have considered the one I do everything first on a fluke but all three?
I used a radius dish to sand the sides before gluing the tops on. Only thing I can think of is it is now winter here and low humidity caused this.

Why else would this have happened?

I was wondering if I should have sanded the neck block differently after creating the radius on the sides, because the top of the soundboard is flat?

I have not figured out how to post pictures yet but as soon as I do...
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Old 01-08-2022, 08:49 AM
BradHall BradHall is offline
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Did you round over the edges on the head (and tail) block? If not, that might be the source of the crack.
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Old 01-08-2022, 08:52 AM
Kerbie Kerbie is offline
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Quote:
Originally Posted by sgabalski View Post
I have not figured out how to post pictures yet but as soon as I do...
Have you looked at this post? PM me if you have any questions and I'll be glad to help.
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  #4  
Old 01-08-2022, 09:00 AM
sgabalski sgabalski is offline
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https://imgur.com/a/XEVOkFF

Last edited by Kerbie; 01-08-2022 at 05:26 PM. Reason: Embedded photo.
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Old 01-08-2022, 09:01 AM
nickv6 nickv6 is offline
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Which way does the grain run in the block?
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Old 01-08-2022, 09:51 AM
JonWint JonWint is offline
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Humidity drop after gluing. Cracks may have been instigated by clamping pressure beyond the rim during gluing. How do you clamp?

No cracks in lower bout?
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Old 01-08-2022, 10:03 AM
sgabalski sgabalski is offline
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Quote:
Originally Posted by JonWint View Post
Humidity drop after gluing. Cracks may have been instigated by clamping pressure beyond the rim during gluing. How do you clamp?

No cracks in lower bout?

https://i.imgur.com/xYytODj.jpg

I drilled holes in the forms and made these cork padded discs to clamp. I did not experience any cracking. The glue up happened a few months ago. I was going to start binding them next weekend and noticed them today.

Last edited by Kerbie; 01-08-2022 at 05:28 PM. Reason: Embedded photo.
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  #8  
Old 01-08-2022, 10:47 AM
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Craig Wilson Craig Wilson is offline
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Quote:
Originally Posted by sgabalski View Post
https://i.imgur.com/xYytODj.jpg

I drilled holes in the forms and made these cork padded discs to clamp. I did not experience any cracking. The glue up happened a few months ago. I was going to start binding them next weekend and noticed them today.

More questions than answers:

Has there been a significant humidity drop since you glued them up?

You say you built in a radius. Has it flattened? Have the rims deformed at all? Have the backs moved?

Did you sand the heel/end blocks to the same radius as the rim linings?

Do the center joint seams look OK?
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Old 01-08-2022, 03:16 PM
LHawes LHawes is offline
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Is the crack offset up and down? Or just widened side to side? If it's offset up and down then the neck block could be the culprit. If it just widened side to side then it looks like shrinkage but why right at and only at the neck block? Did the neck block shrink?
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Old 01-08-2022, 04:05 PM
sgabalski sgabalski is offline
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Quote:
Originally Posted by nickv6 View Post
Which way does the grain run in the block?
Nick


The neck blocks are rift sawn. Close to quarter and run kind of like the grain on the top.
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Old 01-08-2022, 04:08 PM
sgabalski sgabalski is offline
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Quote:
Originally Posted by Craig Wilson View Post
More questions than answers:

Has there been a significant humidity drop since you glued them up?

You say you built in a radius. Has it flattened? Have the rims deformed at all? Have the backs moved?

Did you sand the heel/end blocks to the same radius as the rim linings?

Do the center joint seams look OK?


Yes to humidity drop since they have been glued up.

I sanded the blocks in the radius dish that the sides were done in, at the same time. This is why I wonder if I should have sanded the neck block flatter than the 26’ dish. Because the brace on top of the sound hole is flat.

Center lines seem ok

And no back cracks
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  #12  
Old 01-08-2022, 04:10 PM
sgabalski sgabalski is offline
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Quote:
Originally Posted by LHawes View Post
Is the crack offset up and down? Or just widened side to side? If it's offset up and down then the neck block could be the culprit. If it just widened side to side then it looks like shrinkage but why right at and only at the neck block? Did the neck block shrink?


Weird because all the wood has been in my shop for over a year. One top seems like the block pushed the top up and then it spreads.

I thought I seasoned the wood long enough
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  #13  
Old 01-08-2022, 04:59 PM
Alan Carruth Alan Carruth is offline
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Seasoning wood reduces moisture change, but it takes a long time (decades) to make much difference. It sounds as though you built in some stress (radiused block and flat brace) and then saw an appreciable humidity drop that made it worse.
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  #14  
Old 01-08-2022, 05:30 PM
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Craig Wilson Craig Wilson is offline
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Quote:
Originally Posted by sgabalski View Post
Yes to humidity drop since they have been glued up.

I sanded the blocks in the radius dish that the sides were done in, at the same time. This is why I wonder if I should have sanded the neck block flatter than the 26’ dish. Because the brace on top of the sound hole is flat.

Center lines seem ok

And no back cracks

I think the combination of the radiused block, the flat transverse brace and the humidity change created a perfect storm that the spruce couldn't handle along the grain.
I build all my flat tops completely flat, so I won't offer specific advice on what to do differently next time.
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  #15  
Old 01-08-2022, 05:49 PM
Fathand Fathand is offline
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Quote:
Originally Posted by sgabalski View Post
The neck blocks are rift sawn. Close to quarter and run kind of like the grain on the top.
The grain in the blocks usually run parallel to the quarter sawn sides of guitar. If the sides are flat sawn they would still run the same way I think.

If your top is flat, the top of your neck and tail blocks should be flat to match them and the bottoms should match the back.
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