Attaching the Side Braces pieces are next but before they
can be installed one of them needs to have a hole drilled for the locking bolt
and a threaded T-nut for the bolt to run through that will clamp the spacers in
place. The top drawing shows the hole for
the bolt and the bottom drawing shows the T-Nut installed in a recessed hole so
it ends up flush with the face of the Side Brace. To make the recess for the T-nut I used a
flat bottom Fostner bit then drilled the through hole with a regular twist bit.
To install the Side Braces, one gets clamped in place and
five screws are installed, three from the bottom and two from the Fixed Backer
using the same pilot and countersink hole method as before.
The Spacer Base gets set in place next which is shown in
the top drawing. It’s a 25+ year-old
piece of 2x4 that was salvaged when I remodeled our Master Bath. A couple years ago some of those salvaged
pieces were flattened then made square and true for another project. This off cut is one that just needed a little
trimming to width and thickness then cut to length. With it in place the second Side Brace is set
where it goes. Next is to add the silver
end to end clamp. It pulls the Side
Braces and the Spacer Base tight together.
Additional clamps are added to hold the second Side Brace in place while
the screws are put in just like the first one.
Last is to run several screws up through the Base into
the Spacer Base to lock it into place along with a single screw through each of the
Side Braces into the Spacer Base lock those pieces together.
As the project has progressed, I have been checking all
along to make sure everything was square which it was. However, when checking at this point there
was an unpleasant surprise. The Base and
Fixed Backer were no longer square (insert the many bad words said here). It’s not out of square a lot maybe 3/32” over
the height of the Fixed Backer but it’s enough to make be worry that the cuts
for the box joints would not be square.
With everything glued and screwed together there is not really any good
way to square the two pieces without starting over. After some thought I decided to add a thin
shim at the top of the Fixed Backer which will then bring the Moving Backer
back into square. This is the part the
box joint blanks will get clamped to and be registered for squareness
against. The top photo shows the shim
installed while the bottom photo is a closer look at one end.
Attaching the Moving Backer to the Moving Index Brace is
next. Those two pieces are shown in the
inset drawing below. In use the Moving
Index Brace will set on the Fixed Backer then slid back and forth to make the
box joints. So the Moving Backer won’t
rub on the Base my 24” steel scale is used as a spacer to raise the Moving
Backer up off the base. A close view of
that is in the top photo while the bottom photo shows how it looks with all the
screws installed.
After adding the shim to square up the jig I now need to
angle the top of Fixed Backer (red arrow) so it’s square with the Base. That’s done using a block plane. To help give a consistent angle there are
three layers of masking tape right at the edge of the plane to give the proper
angle.
Another piece whose edge has to be cut at an angle is the
Moving Indexer shown in the drawing.
When measured the angle comes out to 1.2 degrees. Once the table saw is set using the digital
gauge it’s easy to cut the piece to fit.
Installing the Moving Indexer is next and to set the gap
so the finished assembly moves easily but without much play three layers of
masking tape get used as a temporary spacer per the top photo. The bottom photo shows it in place with the
five screws installed but before the clamps are removed. Once the masking tape is removed the whole
assembly moves freely without being loose.
To control the fit of the box joint a Moving Indexer and
Index Guide is required. The original
plan had a wood spacer for the Index Guide that matched the thickness of my
1/8” wide rip saw blade. During the
build I decided to change the blade to a ¼” stack dado set with a .004”
spacer. I will explain the reasoning
behind the .004” spacer later.
The reason for the change to the dado set is that it will give me a
flatter bottom of cut and I will need to
make only half as many passes through the saw to cut the box
joints. The top drawing shows the two
options considered while the bottom photo shows the selected layout and bolt
that will be used for the Index Guide.
Milling the place where the bolt goes is a three-step
process. It’s all done using the drill
press with the Moving Indexer clamped in place.
First, is using a ¾” Fostner bit a half hole is drilled through the
Moving Indexer Brace and into the Moving Indexer. The setup is shown in the left photo. In the middle photo that hole has been
drilled and a ¼” bit has drilled the hole where the threaded part of the bolt
will go. Last in the right photo a
5/16”-18 tap is used to cut threads in the wood matching the threads on the
bolt.
With all of the drilling in the Moving Indexer done I can
put temporarily install my Index Guide (bolt) through it. Here is a better view of the finished Moving
Indexer along the bolt, washers and nut to lock it into place. While the hole in the Moving Indexer has
threads that match the bolt the fact that they are cut into plywood makes them not
very strong. My plan is to use the threads to
register the bolt in place then use the steel nut and lock washer to hold it
there. However, before the bolt can be
installed the end of it needs to be sized which I will do in the next post.
Next Up – Index Guide & Jig Testing
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