AW Extra 3/7/13 – 10 Tips for Gluing Miters

10 Tips for Gluing Miters

By Bruce Wiebe

Every woodworker faces their share of miter joints,
whether framing a mirror, edge-banding a coffee
table or assembling a jewelry box. And even for
seasoned woodworkers, gluing miter joints can be
frustrating. Gaps appear. Imperfect cutting or
gluing leaves the joint misaligned. One of the
boards protrudes slightly at the corner, forcing you
to sand it off, revealing a 1/16-in. strip of
endgrain. Three of the four miter joints in a frame
may be dead on, and the fourth ends up skewed.

Here’s some help. Because there is no “best”
way to deal with gluing-up miters, we’ve given you
a collection of tips, all of which are proven to make
this often maddening process go smoother.

Bored block on slotted base

This benchtop gluing jig lets you see, and adjust, both faces
of the miter joint while clamping it. Hold the joint tight,
without glue, while you clamp one board in place. Then
apply glue to both mitered faces. Push the unclamped board
into place, then add the second
bar clamp.

To make this jig, cut a
diagonal notch halfway
across a 7-in.-square piece of
medium-density fiberboard.
The notch lets you see if the
joint is closed on the underside,
as well as letting the
glue dry thoroughly. For the
clamping block, glue together
two 4-in. squares of plywood,
drill a 2-in. hole in
the middle, and screw this
assembly to the fiberboard with one square corner over the
slot. Be sure the corner of the block is square, or your precisely-
cut 45-degree joint faces won’t be flush when you
clamp them together.

Click any image to view a larger version.

Notched pressure pads

These pads work
particularly well if
you like using
handscrew
clamps. Cut
notches in two
1/2-in.-thick
strips of softwood,
and clamp them
tightly on each
board end so the
notches are near
the middle of the
joint. Tighten the
handscrew gently
against the notches
while pressing
the face of the
joint with a fingertip
to keep the
board edges flush./p>

Handscrews with sandpaper jaws and bar clamps

Put strips of 60-grit sticky-back sandpaper in the jaws of
two handscrews and clamp them parallel on either side of
the joint. Now draw the joint closed by clamping the
handscrews together with bar clamps on top and bottom.

Stacked plywood triangles

If you’re gluing a box with
mitered corners, cut several plywood
triangles, and screw them
together into a triangular block.
Cut off the inside corner so it
doesn’t interfere with the joint.
Without glue, clamp the boards
onto the triangular block, and
when the joint’s perfectly
aligned, remove one board, apply
glue, and reclamp.

Masking tape

Masking tape works well on
wider miter joints that don’t
bear much weight, as in a
jewelry box. Tape the joint
along the middle section first,
apply glue, and close the
joint. Now stretch tape at 45-
degree angles on both corners.
Allow plenty of time for
the glue to dry when you use
tape, because you’re limiting
air circulation.

Packaging tape and web clamps

The strong adhesive and tough plastic of
packaging tape allow it to work as a
hinge on long, mitered corners. After
carefully cutting the miters, lay the boards
outside-face up and side by side so their
sharp edges touch. Apply strips of tape
along each joint, pressing the tape firmly
onto the wood, then flip the boards and
apply glue. Use web clamps to tightly
hold the joints together, and wipe the
squeeze-out from the inside corners.
Again, allow the glue to dry thoroughly
before removing the clamps and tape.

Bessey miter clamp

This clamp works like a dream. At $128 each, though, it’s an expensive
dream. A sliding block pushes on the inside of the joint to snug it
against two pivoting, soft-jawed pressure pads. The pivoting pads
work like a pair of thumbs to align the joint perfectly as they apply
pressure. If you make a lot of miters, this clamp is a godsend.

Pivoting jaw clamp

This clamp, with
pivoting jaws and
razor-sharp teeth,
works great for single
miter joints. But the
barracuda-like jaws
leave nasty scratches
on the wood, so tape
or clamp softwood
strips on the corners
to shield the project
pieces. Reasonable
at $13 each.

Bessey band clamp with pivoting corners

If you’re building smaller miter
joints, give this clamp a try. It
works especially well for assembling
narrow frames that don’t
require a ton of clamping pressure.
It has a geared winder that tightens
and rolls up the band on both
sides, and a handle you twist to
increase the pressure. Slotted
angle-clips press on each corner
keeping pressure uniform. The
jaws on the circular clips adjust to
any angle. $31 for the clamp and
four angle clips. A box of six extra
clips costs $14.

Banding mitered edges

When you’re finishing a plywood tabletop or cabinet door
with mitered edging, cut four short pieces with a 45-degree
angle on one end. The short pieces work great to help size
and locate the edging. Tape and clamp the short pieces in
place on two of the opposite faces, then glue on the first
two edging strips. Remove the short blocks so they don’t
get glued on.

Source

(Note: Product availability and costs are subject to change since original publication date.)

American Clamping Corp., 585-344-1160, Bessey Miter and Band Clamps.

This story originally appeared in American Woodworker April 1999, issue #72.