This is my screw advance box joint jig.
It's designed to make a series of cuts
in the end of a piece of wood with a saw blade or a dado blade.
And to make adjustments quickly and accurately.
And that often makes using a dado blade unnecessary.
It works by having inter-changeable crank gears
which turn one of two gears here
and that, in turn, turns a threaded rod.
And that advances the carriage.
The jig is large enough to handle a whole stack of boards
That can be up to 30 centimeters or 12 inches wide.
And up to 8 boards deep.
I'll demonstrate the jig using two cheap skill saw blades
instead of a dado blade.
My test cut has a width of about
4.38.
So, I want to advance, just under double that amount
for each cut. So I want to go about
8.7 millimeters per cut.
And on my spacing table
the next smallest one is...
8.63.
And for that one I put the 29-tooth gear
against the 16-tooth gear and 3 turns per increment.
I'm gonna need to put the mount in the upper position to mesh
with the 16-tooth gear.
And put that one over here.
Now, one of these needs to be offset by half an increment
which is a turn and a half on here.
So I'll just slide that over.
And now the fingers should align between the two of them.
This one's a little bit tight. To loosen it
I would use a smaller increment.
Because with the same size cutter
a smaller increment means smaller fingers.
Because I adjust the spacing in the jig
I can use any blade and this is the thinnest blade I could find.
And with that I made this very fine box joint in this box.
The other way to make joints with this jig is to use
the 48-tooth gear against the 12-tooth gear.
And that gets me 4 turns of the threaded rod
per turn of the crank. And at 16 TPI, that means
1/4 inch. And then I make a test cut
using the blade. Back it up
and then forward again until I can make the cut
just adjoining to that. And then I mark the position
on the large gear that I had for that particular cut.
So now with this set-up I make one cut with the crank here
and the other one with the red piece of tape here.
And then I finish the turn and add another turn
for the next cut. Now that can be a bit complicated
but I have an entire video explaining how to set that up.
So, this joint is too tight for gluing.
So I need to loosen that up by moving the tape
just by a small increment.
So, I re-cut that joint in 50 seconds flat.
And this is what it fits like now.
Of course, I'm not limited to making joints in boards.
Here's a joint made in two pieces of 2 by 4.
So, if you want a cool box joint jig, like this.
You do have to build it. But I have a whole
video series on how to build it.
And I also have a very detailed set of plans
available for sale on my website.
I'm sorry but they do cost money.
I do charge for some things.