Make the beams from 1/2" MDF and 1/4" tempered hardboard.
Both materials are quite flexible–and that’s actually an advantage.
Unlike plywood, which can be warped, these materials will
stay flat and straight as you build the beams.
A simple requirement is the key to success: you must be able
to saw a straight line. To accurately cut large sheetstock, you
should have an outfeed roller or table behind your tablesaw. It
also helps to have a similar support in front of your saw.
The beams are 6" square and can be made any length you
wish. They’re best made in matching pairs, so you should cut
enough parts to make two at a time. I’ve found that pairs of 4',
6' and 8' beams fit all my needs. To build this set of three pairs,
you’ll need two sheets of MDF and two sheets of hardboard. But
even one pair, of any length, is handy to have around the shop.
Mill the parts
Begin by cutting the top and bottom pieces to length and width
(see Cutting List, below). Cut the side pieces to final size, too.
Cut 3/16" deep grooves to receive the sides (Photo 1). Make
them about 3/16" wide, using a standard blade. (The hardboard is only nominally 1/4" thick; its actual
thickness is usually closer to 3/16".)
Make the first pass on each piece with
the fence set 1" from the blade. Then,
move the fence approximately 1/16"
and cut a second set of grooves. Make
a few trial cuts in scrap stock to get
the correct fence setting–it's a fussy fit.
When you’re done, the sides should
drop into the grooves with little or
no resistance. Use featherboards to
ensure that the grooves are parallel
and have a consistent depth.
Next, cut the web pieces to width
and length. Their exact dimensions are
determined by the width and depth
of the grooves. First, rip one or more
blanks to width (Photo 2), then cut
the web pieces to length (Photo 3).
To make the beams comfortable
to handle, rout a 1/8" roundover
on all edges of the top and bottom
pieces. Check that all the sides fit
into the grooves (there may be some
variation in the hardboard’s thickness).
If one edge is too thick, sand
it with 80 grit paper until the piece
slides in the groove. Break all the
edges of the sides with 80 grit sandpaper
so they will be easier to fit into the grooves when you glue the
Mark the locations of the web pieces
on the bottom piece (Photo 4). Space
the outer web pieces 1" in from the
ends. Space the remaining web pieces
about 8" to 10" apart.
Create a level surface for gluing
the beams. The easiest way to do this
is to use one of the beams itself as a
gluing platform (Photo 5). This is an
important step. If you were to glue the
beams on a bowed or twisted surface,
they wouldn’t come out straight.
Place the bottom on the platform
and run a generous bead of glue down
both grooves (Photo 6). Next, drop
the sides into the grooves. Run a thin
bead of glue around all four sides of
each web piece, and stand them on
their lines (Photo 7). Run beads of glue
down the grooves in the top piece and
put it in position, starting at one end
(Photo 8). As you lower the top, the
sides will automatically align with the
grooves. Make sure the top is seated
along its full length by sighting down it
or placing a straightedge on it.
Clamp every 8" or so, or simply
place weights (bricks or cinder blocks)
on top of the beam.
This story originally appeared in American Woodworker June/July 2010, issue #148.
June/July 2010, issue #148
Purchase this back issue.
1. Cut shallow grooves in the top and
bottom pieces of the beams. The sides
should fit loosely in the grooves. Make two
sets of parts, to build a pair of beams.
2. Rip a blank for the web pieces. Make
it exactly the same width as the distance
between the grooves.
3. Temporarily assemble the top, bottom
and sides. Crosscut the web pieces so they
exactly fit between the top and bottom.
4. Disassemble the beam and mark
lines across the bottom to locate the web
5. Assemble one beam, without glue,
and turn it on its side. This creates a level
surface for gluing up the other beam.
6. Place the second bottom piece on the
clamped-up beam. Run a thick bead of
glue down both grooves.
7. Place the sides in the grooves. Apply
glue to all four sides of each web piece and
stand them in position.
8. Apply glue to the top piece and drop it
in place. The next day, use this beam as a
support for gluing up the other beam.