Tops cracked at neck block!!!

[sgabalski]

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...

[BradHall]

Did you round over the edges on the head (and tail) block? If not, that might be the source of the crack.

[Kerbie]

Originally Posted by sgabalski

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.

[sgabalski]

https://imgur.com/a/XEVOkFF

[nickv6]

Which way does the grain run in the block?
Nick

[JonWint]

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?

[sgabalski]

Originally Posted by JonWint

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.

[Craig Wilson]

Originally Posted by sgabalski

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?

[LHawes]

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?

[sgabalski]

Originally Posted by nickv6

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.

[sgabalski]

Originally Posted by Craig Wilson

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

[sgabalski]

Originally Posted by LHawes

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

[Alan Carruth]

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.

[Craig Wilson]

Originally Posted by sgabalski

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.

[Fathand]

Originally Posted by sgabalski

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.