If I want to join two pieces of wood, like this
the strongest would be some kind of box joint or finger joint
like this one. And in this video, I'll show you how to
set one of these up with my screw advance box joint jig
without a dado blade.
For a 1/4 joint spacing, it's best to switch over to
the 20 tooth gear. And I'll match
that against the 12 tooth gear.
which will give me 4 turns on the threaded rod
for every turn on here.
And with 16 threads per inch on this threaded rod
that means every turn on this crank
will move the carriage by a quarter inch.
And I'm gonna use just a regular saw blade
but I'm making multiple cuts with that
I'll hog out the quarter inch slots.
And the question is at what angle
do I need to make these cuts
on this gear to get that slot.
So, I lined it up so that the blade is just inside the box
and I positioned the gear so that
the handle is right up against
here, which I'll consider home position.
Now for my set-up, I'll make the first cut 1/4 inch in.
That's just one turn on this wheel.
And I'll make that cut.
Now comes the set-up part of this
I need to make another slot that is just next to this.
So, I need to move over and I'm gonna start from the same side.
And just make sure that I'm
gonna be cutting flush with where the other one is
and that should be about here.
So I'm gonna use a piece of electrical tape
to mark that gear position.
Now, this position here is gonna
be the start of the 1/4 inch slot.
And then if I go all the way over here
if I want full 1/4 turn
I would move it by a 1/4 inch but I want to do it
less than the thickness of the blade.
And I already established that going to here
is actually going to cut all the way out to this position
because this arc here represents the thickness of the blades.
So, I just have to cut here
and cut here, except that will leave a gap so
I'll make another cut halfway in between.
And, just for convenience, I'm gonna also mark that
with a piece of tape. And now it's time to cut a test joint.
And I'm just gonna use the other end of this piece of wood.
And another piece of wood which I'm offsetting it by
1/4 of an inch.
And I'll clamp with this.
And now to cut the first slot, I
do the first cut at home position.
Another cut here.
And another cut here and now I've hogged out a 1/4 inch.
And this is moving a full 1/4 inch.
Now I've moved a half and inch from the start
and we'll cut again here.
Here and here, once again.
Here, here, and here
and so on.
Now this joint is too tight
because if I put glue in there
that'll be really hard to assemble.
To loosen the fit of this joint, I want a wider cut
So I'm gonna make my last cut just a
little bit further down the line.
And that'll loosen the fit.
Still on the tight side but I'll leave it at that.
If you make a lot of joints like this, it might be worthwhile
to make something like this
which allow you to get the glue into multiple fingers at once.
I think I've got enough glue in there.
There's nothing like a belt sander
for making things look precise.
With this joint being just a demonstration piece
I figure we might as well break it to see how strong it is.
Well, holding up my weight.
For a bit.
And it broke the wood, not the joint.
I guess for soft wood, the slow growing stuff is much stronger
because this part grew real fast
and it just broke apart.