I've done some joint strength testing using a
ball jack on a bathroom scale
but as I pump that jack, I always have to
let it go to see what the force is.
So I though something with a slowly
increasing force would be better.
My thinking is to have a threaded rod
and a nut that's turned down on that
and that would push the threaded rod
slowly up. So the nut would have to
push against some kind of washer
and then the threaded rod has to slide in
some sleeve, just to hold it in place.
And to keep that threaded rod from spinning
as I turn the nut, I need something on the
end to keep it from turning, and so I took a
coupler nut, drilled a hole through it, and put
a shaft through there and I also cut it off.
And that screws on the end, like so.
To turn the nut, I'm thinking of putting some
kind of wooden gear around it, like this gear
from my box joint jig.
And I've printed out templates to make
another gear of about that size
and a smaller gear to drive it with.
I designed these gears with my gear generator
program and they're designed to mesh
perfectly when they're both on the same
plane. But I want to mesh them at a
90 degree angle and...
that's a bit of a kluge and it generally
works better if you bevel the sides
of the teeth by about the same amount that
the complimenting gear has a pressure angle of.
I just tilted my bandsaw by 14 degrees.
And I put this on here and I cut
just a little bit into it. And that will
prevent tear-out on the bottom of the gear.
I cut the angle on 1 side of the teeth
and to do the other side, I need to tilt the
bandsaw the other way. Which, of course,
it doesn't. So I rigged this up to get
the other tilt.
With the sides of the teeth beveled like that,
they end up very skinny on the back.
But that does leave a lot of slack. So these
will never jam and what I should have done
is to fatten the teeth a little bit in the design
so that I get a snug fit and stronger teeth.
With the big gear on a nut,
I now need a way to hold
the little gear on here.
And for that, I've put the bushing
in a block of wood. And so that's gonna
go on here,
like so.
And then a block of wood against here.
With a shaft through there and then a gear
on here. I drilled an undersized hole in the
gear. And I'm also gonna glue this bit on
here and drive the shaft through both of those.
Now I take the other one off.
So I need to put some glue in there.
And some clamps on it for good measure.
While this gear's turning, it's also exerting a
downward force on the big gear.
And to support that gear against that, I
figure I should put a bearing embedded
in here, like so.
Now I need something on the bottom to
keep this thing from turning. And I came up
with 2 blocks like this that I'm gonna attach
here and that will also guide the end of the
threaded rod by the nut here.
My plan is to spin this here with a hand drill.
But I don't want to have to chuck one on
here every time because it's heavy and it
affects the tests. So, I'm thinking of
just mounting this bar on here and having
this thing to spin this at a distance
with the drill.
Let's do it.
OK, time to give this a try. I have it on a
bathroom scale and it's on dowels
so it can roll back an forth, so I get no
sideways force. I'm gonna apply this first
20 centimeters from the joint,
and check this out.
Pocket holes.
So that failed with 65 pounds, just
20 centimeters from the joint.
So, next I should try it with some real joinery.