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End grain glue joints stronger?

#4
Not me! The end grain strength is counterintuitive, but his demo is pretty convincing. One thing he didnt mention which is common in my experience with end grain: glue starvation as it gets soaked into the end grain. The joint strength is only as good as the glue, so what happens with end grain when it sucks all the glue up? "Maximizing long grain strength" sounds like a scarf joint to me, so I wont be doing end grain headstock joints any time soon.
 
#6
wouldn't a scarf joint be an end grain joint, just with more surface area?
Speaking of scarf joints, I still haven't figured out the point of a scarf joint being so far down into the neck.
Does it have something to do with head stock angle? If it does, it seems like it would make more sense to do the scarf in the headstock itself.
Then again, I'm relatively new to instrument building. But I've been able to understand most of it so far. The neck scarf joint I'm still struggling with.
 
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#7
I see a scarf joint as one edge grain and one slightly off edge at around 8-13 degrees or so off from parallel to the grain. In this video the guy goes full perpendicular to the grain.

As for going so deep into the neck, the scarf has to be the thickness of the neck, and transition from the bottom of the neck to the fingerboard at a certain angle. Math is in control here. I'm doing a mandolin with a friend and his 14" scale neck has almost 7 inches of scarf joint in it. :woot:
 
#9
RichterScale said:
I get the gist of the joint itself, I just have a hard time understanding why it's in the neck.
Click to expand...

Where else would you put it? In the headstock, which is only about half an inch thick, it would be rather fragile, at the neck headstock transition there's usually too much wood removed to allow for the truss rod adjustment nut for that to be a suitable place. below the headstock in the neck allows for longer surface area contact due to neck thickness, plus the truss rod adds rigidity, then you have the glued on fretboard, often with a counteracting grain direction to help add stiffness and strength.

Al up, if you have to have a scarf joint in anywhere in a neck neck, that's about the best place to have it.
 
#10
I know it's done by many builders and I know it works. It's just one of those things that I look at and it feels "wrong". I have no good reason or argument against it.
I also have no good reason for not putting fruit in beer. People do it successfully all the time. But when I look at it, it just seems wrong.
 
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#12
RichterScale said:
I know it's done by many builders and I know it works. It's just one of those things that I look at and it feels "wrong". I have no good reason or argument against it.
I also have no good reason for not putting fruit in beer. People do it successfully all the time. But when I look at it, it just seems wrong.
Click to expand...

Well whether it seems wrong or not, you did ask the question and I gave what seemed to me a logical answer, if it seems wrong to you, I guess you can do something else.

I don't do scarf joints, but either do offset headstocks like Fender, or build laminated necks where each section is cut to match a template with the headstock angle included, then I glue them up, add side wings with alternately running grain. So I cut a number pf pieces something like the pic bellow and glue them up. That way I can alternate the grain and combine flat sawn and quarter sawn to add stability. I started building necks that way back in the late 70's, so 'hippie sandwich' era, but they seem to work pretty well, so I've kept doing it. I'm sure I'm not the only one...;)






P9060358 (2).JPG
 
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#13
It makes sense to me that an end grain-to-end grain glue joint can be stronger than a side grain-to-side grain glue joint, if all else is equal. The glue will probably get a better grip into the fibers of the wood in the end grain.

But.....That depends on several big factors. Like GilmourisGod said, a critical thing is that the glue doesn't soak in to the end grain too much and starve the joint. Likewise, if there's any gap filled with glue, the glue needs be able to fully cure. Many woodworking glues have a real problem curing in the middle of a joint, if they can't get enough moisture and air.

*Side note: I've got an upcoming thread about that. Some interesting things that Rob Allen and I discovered about gluing roasted maple.

The other factor about an end grain butt joint is that it's usually very small cross-sectional surface area. As compared to most side grain joints, which have much more contact area. The butt joint, in bending, will have very tensile load on one side. And we know from experience that a glued butt joint will break easily in bending. A fair test is a side-grain joint of the same cross-sectional size and area. In that test, I can believe that the end grain joint will be stronger.

The scarf joints commonly used in instrument necks are actually half-and-half; end grain glued to side grain!
 
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#17
As one commenter said,

"It would be really interesting to see what happens to the strength over time as the side to end grain joint grows and shrinks with changes in humidity. I’ve always thought that this was what caused these joints to fail, not just the differences in the grain direction. The new glue strengthens the joints as you demonstrated but doesn’t the glue fracture and become weak as the wood swells and shrinks over time. This is my concern - that my project is strong when it leaves the shop but a few years later it begins to fall apart."

There are literally millions of woodworkers who have been doing woodworking for decades or more, but this guy is right. Right. o_O
 
#19
Miter joints are common end grain joints... ;)

Many experienced woodworkers know that end grain can be successfully glued if done correctly, as in correct stock selection, pre-sizing the joint with glue, and using enough glue.

Properly dried, furniture grade stock, vs. construction lumber, pitchy, or oily wood, helps the odds of a good end to end joint, as there is far less moisture to possibly interfere with the joint, and the material should move less over time. Wood can be thought of as a bundle of straws, so any extra moisture will migrate to the end grain, and the end grain will soak up far more glue, creating a starved joint.

So, do it right in the right stock, and you'll be fine.
 

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