Glue Test on Baltic Birch

[msprague]

After having one of my horns break after dropping a cabinet from about 3 feet, I decided to do a glue test. Granted, it's not the most scientific and I could have used a larger sample set but it gave me a reasonable idea of the strength of the different glues I use. I had built a horn out of 1/2" Baltic birch with a PSD2002 and the weight of the driver caused the middle joint to break.
http://www.mikesprague.net/LineArray/ph ... 20001.html
I have since added two reinforcing ribs down each side but I wanted have a better understanding of the glue strength.

I performed two different test: an end to end joint and a butt joint using:

• Gorilla glue (wetting the joint first)
  Gorilla glue (dry)
  Titebond II
  5 minute Epoxy

I used consistent test parts and same lever arm to break each joint with a digital scale and wrote the pounds of force required to break each joint on the wood shown here.
You can see the the gorilla glue didn't tear the wood at all and gave up pretty quickly.
http://www.mikesprague.net/GlueTest/pho ... _1991.html
http://www.mikesprague.net/GlueTest/pho ... _1992.html

[sine143]

Um, why no pl glue?

[Bill Fitzmaurice]

Um, why no pl glue?

+1. We've had people drop cabs off the back of pickup trucks going down the highway and joints with PL did not fail. There are reasons why the plans specifically state Do not use traditional woodworking glue.

[msprague]

I will give PL a try - I thought it was similar to Gorilla glue - being a polyurethane glue, so I considered PL equal to Gorilla glue but I guess that is NOT the case.
I've always had good luck with Titebond II and, in my simple testing, was as strong as the wood itself. The yellow glue just cleans up nice and I've seen pictures of the insides of some boxes built with PL and they look sloppy. I like the inside of the box to be as nice as the outside but will get some PL first chance I get.
I did find this article on the subject:
http://www.popularwoodworking.com/artic ... thane_glue
From this article PL sounds about the same strength as yellow glue but has a wider range of application.

More testing to follow

[Grant Bunter]

The yellow glue just cleans up nice and I've seen pictures of the insides of some boxes built with PL and they look sloppy. I like the inside of the box to be as nice as the outside but will get some PL first chance I get.

PL premium, if left for a number of hours, but before it gets to hard, can be made very clean, with a scrape using a sharp chisel.

I did find this article on the subject:
http://www.popularwoodworking.com/artic ... thane_glue
From this article PL sounds about the same strength as yellow glue but has a wider range of application.

More testing to follow

Interesting read, but not definitive as half the article was based on subjective observation only.
There's a whole range of PL products, so the one to test would be PL Premium...

[sine143]

The most relevant subject matter in that text is the references to how yellow glue contracts, and poly glue expands. this is one of the most important features, even beyond strength given the importance of our horns being airtight

[Bill Fitzmaurice]

I... will get some PL first chance I get.

That should have been with the first of our cabs that you built. You're extremely lucky that you haven't had leaking joints. Assuming, that is, that you don't.

[sine143]

Just waiting for djphatman to chime in. his signature is perfect for this thread

[Radian]

From this article PL sounds about the same strength as yellow glue but has a wider range of application.

More testing to follow

Henkle already has that data on file....and it's moot at this point.

You're assuming because two materials have nearly the same yield strength, they are identical in application. Not a good idea.

It's not a matter of simply pulling two pieces apart. You have to keep tabs on the energy going into the test to see which joint is absorbing more or less. Calculate the area of the elastic region of the stress-strain plot (aka Modulus of Resilience) to see how much energy each glue can absorb before yielding....or perform a legitimate impact test. That'll be where the major difference lies.

Being that construction adhesives are typically supplemented by elastomeric tougheners, they will trump wood glue in that department any day of the week.

There's a lot more to applied adhesive chemistry than just the yield strength. Follow the plans, use PL Premium.


P.S.- For testing purposes you'll need to know that wood glues cure through and through within 24 hours, yet PL Premium (like most polyurethanes) takes ~7 days to fully kick.

[DJPhatman]

Just waiting for djphatman to chime in. his signature is perfect for this thread

Here ya go!

[MissileCrisis]

P.S.- For testing purposes you'll need to know that wood glues cure through and through within 24 hours, yet PL Premium (like most polyurethanes) takes ~7 days to fully kick.

I'm not arguing PL btw, I'm just curious about this tidbit of information. I found it rather interesting that my Duratex said 7 day dry time (full cure), and now I just learned that PL is 7 days as well... Why is that? I proved to myself that it doesn't harden when it looks dry (duratex) by accidentally dropping a T60 onto asphalt and getting all sorts of scrapes to patch up.

[Radian]

Why is that?

Because that's just the way the chemistry works out.

It's the cross-linking process that gives either material its characteristic toughness. That process takes time.

[ncgrove]

Why is that?

Because that's just the way the chemistry works out.

It's the cross-linking process that gives either material its characteristic toughness. That process takes time.

Start here: http://en.wikipedia.org/wiki/Organic_chemistry

It takes a year of general chemistry to learn enough to take a year of organic chemistry, which will provide you with almost enough knowledge to start learning about polymers.

[67baja]

Why is that?

Because that's just the way the chemistry works out.

It's the cross-linking process that gives either material its characteristic toughness. That process takes time.

Start here: http://en.wikipedia.org/wiki/Organic_chemistry

It takes a year of general chemistry to learn enough to take a year of organic chemistry, which will provide you with almost enough knowledge to start learning about polymers.

I absolutely hated O-Chem. Taught by a woman with a name 59 letters long that learned (bad) English as her 75th language. I learned to just read the labels of glue instead of trying to figure the chemistry behind it.

[MissileCrisis]

I'll take your word for it . Chem never was my thing, even though I'm good at it. That's why I became an EE, so much easier figuring out circuits . Unless of course they are using minuscule SMD parts that you have to use a microscope to see, like what I'm working on.