Help with joint and structural integrity - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 03-16-2015, 12:04 PM Thread Starter
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Help with joint and structural integrity

Had a mishap while finishing up this guitar neck, and I had to thin it down to the lowest point, which is too thin. The headstock is .3" right now, and I need it to be .5". My original idea was to just put a couple of .1" laminations to make up the thickness I need, but I got worried about the strength. I thought a dovetail wall would offer more strength, so that's what I went with.



I'm now thinking it would it be stronger if I glued a thin piece of face grain walnut to the wall of the dovetail, miter the bottom to accept the walnut lamination on the face of the headstock, and then repeat with another veneer maple the same way -- face grain glued to face grain walnut and mitered at the bottom to accept the veneer of maple glued to the face of the headstock. I'd love to hear what you think of the idea or if you have any ideas on how to make it better.

For those not familiar, this is what the final shape/transition will look like.

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post #2 of 10 Old 03-16-2015, 12:12 PM
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my opinion is that it is necked down too much for the kind of stress that the strings will apply. i don't think laminations ending in that dovetail are going to add enough strengeth to work.
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post #3 of 10 Old 03-16-2015, 09:03 PM
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Where is your truss rod set? Could you cut the headstock off at a low enough angle to make a scarf joint? Many guitars use scarf joints for the headstock, and they hold just fine.

This will only work if you can make the cut without sawing into your truss rod channel.



Simon
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post #4 of 10 Old 03-16-2015, 09:19 PM
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That maple neck is going to be strong enough to do the job. I wouldn't worry about it structurally. I would laminate a different species of wood on the inside like walnut so it looks part of the design. Nobody will ever know the difference.
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post #5 of 10 Old 03-17-2015, 07:57 AM
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A regular set of guitars stirings in the 10-48 range applies around 100 pounds of force to the headstock.You also have to consider this is continuous force being applied to wood.
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post #6 of 10 Old 03-17-2015, 09:04 AM Thread Starter
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Quote:
Originally Posted by 2lim View Post
Where is your truss rod set? Could you cut the headstock off at a low enough angle to make a scarf joint? Many guitars use scarf joints for the headstock, and they hold just fine.

This will only work if you can make the cut without sawing into your truss rod channel.

Simon
That thought had crossed my mind as well, but I just don't think I've got quite enough meat there to make it work.

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Originally Posted by Steve Neul View Post
That maple neck is going to be strong enough to do the job. I wouldn't worry about it structurally. I would laminate a different species of wood on the inside like walnut so it looks part of the design. Nobody will ever know the difference.
Yeah, since the body of the guitar is walnut and there's a middle lamination of walnut in the neck, the plan was to do a walnut laminate followed by a maple laminate to tie it all together.
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post #7 of 10 Old 03-17-2015, 09:07 AM Thread Starter
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Originally Posted by mako1 View Post
A regular set of guitars stirings in the 10-48 range applies around 100 pounds of force to the headstock.You also have to consider this is continuous force being applied to wood.
True, but the direction of the force is more parallel to the grain rather than perpendicular, so that does mitigate the stress somewhat.

Last edited by RogerC; 03-17-2015 at 11:21 AM.
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post #8 of 10 Old 03-18-2015, 02:15 PM
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The thing that works in your favor is that the bending stresses caused by the string forces will put the top in compression. In other words the added laminations that are butted up against the dovetail will be pushing into the dovetail, not pulling away. Therefore at that critical section, the end grain glue joint will be in compression.
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post #9 of 10 Old 03-18-2015, 11:40 PM Thread Starter
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Good point, Terry. I hadn't thought about that part of it. I was purely stuck on the "end grain glue joints are bad news" portion. This is how I've tackled it so far...














I let that dry for about 24 hrs then trimmed it down and sanded it. I think it turned out well.




Then tonight I formed a block of maple to fit and glued it in place.



I'm cautiously optimistic about it at this point.
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post #10 of 10 Old 03-19-2015, 12:26 AM
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I would be very curious as to how that would effect the tone.I know it's above the nut and should not have much effect but you know how anal us guitar players can be.Was that NOS glue you used?
Just kidding another string bender and good luck with the fix.


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