Man, quite the controvery from my pocket hole tests.
I thought, isn't it obvious that pocket holes
aren't very strong?
But, to satisfy everybody, I decided to re-test
with glue. And to do that I have to use
the same wood and I've already thrown
that wood in as a firewood, so I had to go
back to my big country workshop
and retrieve the sturff from the firewood
so I could cut some more samples from it.
And then I made some more pocket hole joints
but with glue this time.
I just re-used the other ends of the pieces of wood
See, this was pocket hole test originally.
And this used to have tenon, nope actually
that was a dowel joint. So I've got
all these pieces from the same wood
that I'll be able to compare those fairly
with the other ones that I've done
and they've all got glue on them.
I think what people believe is that
if you glue the pocket hole joint,
it's like a butt joint and a screw joint together
and it should be as strong as the sum of the
two of them, but I suspect that's not the case
because the screw joing, the pocket hole joint
tends to yield a little bit before it reaches
maximum strength, wheras the butt joint
does not yield. So, I expect one to break
and then the other to break.
OK, here goes glued pocket hole joint number 1.
I'm on there good.
60
That was just slipping in here. The joints
still good. 80
85
Scale is just under 90
The joint has got a crack in it already
so I suspect that butt joint is not adding
much anymore. 100.
105.
Well, that got up to 115.
And now it's failed.
So I just realized, uh oh I forgot to measuire
where I applied the force.
And the divit is right here.
And I got lucky because that ends up at
exactly 15 centimeters.
So, this test is still good.
Alright, glued pocket hole test sample number 2.
Now it's opening iup and we're at 90 pounds.
Oops.
And we're at 110.
115.
Ooo, 125.
That didn't stay there, though.
So this one got to about 130 pounds.
My third pocket hole sample.
That's 50 pounds, and I think that
just cracked open.
Yeah, that one's not doing super well.
Oh, 110 pounds.
And it went.
And the butt joint's already opening up.
70.
Oh, this one's not doing well.
Think that was about 75 pounds.
And the butt joint has already opened up.
But we're at 115, as much as 120
before it goes.
What's interesting is the joints are failing
a little bit differently this time.
I'm getting this screw head pulling through here
wheras last time I always had this screw
pulling out of the wood, so possibly the glue
helped a little bit or possibly that I had my
jig set up a little bit differently, because I'm
getting a point coming out of the other side
on every one of them, which means I have
a bit more thread in the wood here.
Of course that also means it weakens it,
just a tiny bit here.
There's a couple more joints that I made
with some other scraps before I retrieved
the other ones from my big country shop.
And this is a slightly lighter wood.
I rejected that wood initially because
when I weighed it, it was lighter and that might
bias the tests. And I don't have the screw
penetrating on the back here.
So, just out of curiosity, let's see how
these ones will do. Slightly lighter wood,
pocket hole test number 1.
And, of course it's glued.
OK, the glue joint opened up and we're at
65/70 pounds.
And that one only went to about 80 pounds
to fail. Here's the second one of my tests
with the lighter wood. And I put that one on
with the pocket facing the other way around
because there's not very much glue squeeze out
here and plenty here, so I want to give that one
every advantage to having all the glue where
the tension is gonna be.
OK, glue just popped and we're at 55
pounds or so.
And that one, again, didn't even reach 80 pounds.
And look at these two. Both of the failed
by the screw thread pulling out of this
piece here. And it had less penetration than
the other ones did. But this would be more
the correct set up because you really don't
want the point of the screws sticking out
the other side of the wood.
And, of course, they are at a disadvantage
that even though this is wood from the same
batch, so to say, these two pieces were
a bit lighter so I rejected them initially.
Now, just out of curiosity, I've also made some
butt joint samples because I wanted to see
how much the butt joint is actually able to
cointribute to the pocket hole joint.
Butt joint sample number 1.
Well, that failed at under 40 pounds.
50
That failed quick.
So I hope this gives you appreciation for
the difficulty in running tests like this.
Really difficult to get consistent results
because there's so many factors that affect
joint strength. And on every one of my
pocket holes, with the glue, the glue failed
before the joint actually reached its ultimate
strength so I don't believe that the glue joint
actually contributes to the ultimate strength.
And I think the main reasons these ones
were maybe about 20% stronger than my
previous pocket hole tests
is that I over-penetrated on the screws and
actually had them sticking out the back.
I was just editing my video and this is the one
that only did 75 pounds wheras the other one
did about 120 pounds and looking on here
the screws hardly penetrate out the back at all.
Just a little bit here, wheras the ones that did
120 pounds, had a fair bit of screw sticking
out the back.
And these light ones, which are 8% lighter,
nothing sticking out the back.
So I think the degree of screw penetration
is really what made all the difference.
So, this is one of the lighter ones that wasn't
very strong and this is how far the screws
went in so, they just about went through is
I think this is the correct amount screw
penetration that I should have used for
all the joints.