Glue joints and grain directions

[Bizman62]

I recently stumbled upon a new video where they tested angled joints. The results were surprising, a finger joint isn't the strongest when pulling straight like the front of a drawer.

Today I tried to find that video and found a more interesting one. End grain joints, come on?!? Don't we all know that they're prone to fail?

 

[henrim]

To me, it's not so much about being afraid that an end grain joint would fail. It's more about the unnatural look of the joint. There are of course cases where end-grain joint can be visually appealing, but in general that look is cheap.

[Bizman62]

1 hour ago, henrim said:

To me, it's not so much about being afraid that an end grain joint would fail. It's more about the unnatural look of the joint. There are of course cases where end-grain joint can be visually appealing, but in general that look is cheap.

As was clearly stated in the last third of the video, solid longitudinal wood is many times stronger than any glue joint which for us means that you can't extend your neck with an end grain joint. Moreso, starting at about 13:50 he talks about geometry. about the length of the joint v.s. the length/width of the pieces. The example shows that narrow cross grained pieces are very easy to snap anywhere as the lignin bond breaks whereas an end grain joint can stand quite some bending forces. We don't have to worry about that as the only place where long cross grained wood is being used in luthiery is the band covering the bottom seam inside an acoustic guitar.

[henrim]

Yes. I guess I was't clear. What I meant is my first concern with direct end grain joints is not the strength but the looks. I don't have to consider the strength because I don't do them. Obviously I wouldn't extend a neck like that. If I had to, I think I would do something like the Taylor joint in the attached picture. Both for aesthetics and strength.

[Bizman62]

12 hours ago, henrim said:

something like the Taylor joint in the attached picture. Both for aesthetics and strength.

Isn't that a type of a finger joint? And doesn't it work similarly to multiple biscuits? I know it's a common way to increase gluing surface and make huge beams for buildings so it's definitely a valid way to make a strong joint. But is it stronger than plain longitudinal wood?

Part #3 of the series:

Part #2 is also interesting, combined the three are less than an hour to watch.

[henrim]

45 minutes ago, Bizman62 said:

Isn't that a type of a finger joint? And doesn't it work similarly to multiple biscuits? I know it's a common way to increase gluing surface and make huge beams for buildings so it's definitely a valid way to make a strong joint.

Yes, a finger joint. Technically biscuits or dowels would do pretty much the same. That kind of finger joint is usually used when gluing laminated boards from short pieces. By making the seam visible, Taylor has made the technical joint a design detail though. Nice if you like it. I do.  

45 minutes ago, Bizman62 said:

But is it stronger than plain longitudinal wood?

That is a question I guess the linked video answers? I may check that later. But I don't think I have ever really thought joinery from that perspective. I only do joinery if I have to. For example a scarf joint. Main reason is to save material. Or if there isn't enough material to begin with. A scarf joint has other properties over a neck carved from a one piece, but they are not really the reason I would make the choice. I know there are lot of stories about cracked LP headstocks. And I know they do crack more easily than some others. I just haven't experienced it myself, regardless of not always treating my LP's so well. So, if I have enough wood I make a one piece neck. If I don't, then I join some pieces some way. Which has been a scarf joint for all the two piece necks I have done. But I would like to try a finger joint or dove tail, just for the looks.

[henrim]

11 minutes ago, henrim said:

I may check that later.

I took a coffee break and watched the video. That was good. Pretty much how I figured it would be with the biscuits. Although the reason I use dowels (or biscuits when I have access to a Lamello machine) is mainly to keep the pieces in right place in assembly. Any additional strength they give is a bonus. If you have ever made for example picture frames you know what I'm talking about.

Also in my mind biscuits/dowels can help keeping seams more stable against humidity changes. Now there's an other myth to debunk  They probably just makes things just worse because different species react differently to humidity...