Edge Gluing Techniques #6
Video that accompanies this article can be found
Edge gluing thin slats for panels
and decorative flooring.
Edge gluing is used
in such applications as decorative floor edging or panel making and
can be done in a vacuum press with high quality results. Two key
factors will affect the quality of the end piece; the straightness of
the edges and uniform thickness of your slats. If the slats have a
slight curl, the pressure from 1800 lbs/sq.ft. will normally flatten
them with out any problem.
There are two methods
to provide the side pressure necessary to get good edge glued joints.
Both require a "sled" to hold the material (P1). The base is just
plywood or MDF and a 90 degree corner is attached to one side and one
end. The height of this right angle is about 1/8" less than the
thickness of your finished piece. All the edges are rounded over to
avoid a sharp edge that could puncture the bag. You want to coat the
sled so that glue squeeze out does not stick the work piece to the
The first method was
worked out for a customer making decorative flooring. He had a 6" x 8' x
3/8" plywood base. To this he glued three 2"x 8" x 3/8" slats that
were of different woods. You can also use this same techniques for
inlays. In this case all the material was sized the same, thus an
excellent fit along the edges and no "humping up" of the slat. The
sled was made to accommodate eight completed edges (4'x8'). Glue is
applied to the parts and then placed in the sled against the right
angle fixture. A very thin strip of plastic is placed between it and
the next lay-up to prevent glue squeeze out from sticking the two
Here the sled is in
place in a vacuum frame press, if using a vacuum bag, just slide the whole assembly
into the vacuum bag (P2). The bag will apply side pressure along the 3/8"
edge. We will assume the vacuum is about 24" Hg, thus 12 pounds per
square inch. Since the edge is 3/8", this gives us 4.5 sq.in. per
linier foot times 12 psi for a total of 54 pounds per linier foot or
432 pounds along the 8' length.
To increase the side
pressure we can add a 3/4" x ¾" x 8' strip along the open edge (P3).
Ideally, the end slat overhangs the 8' length of the base by a small
amount. This way we have doubled the surface area for vacuum to apply
its force and generate around 800 pounds along the 8' length. Since
the slats are dimensioned to a close tolerance, this step may not be
required. It may be enough just to apply hand pressure along the edge
as full vacuum is drawn.
The second method
involves the use of a wedge to apply side pressure. This method was
developed for a manufacture of bamboo panels. In this case the bamboo
is not of uniform width or thickness. It is approximately 2" wide and
¼" thick. This method also requires a sled, however, it needs to be
about 3" wider than the panel. An angled stop is added onto the
additional 3" (P4). This is used to contain the wedge that will force
the slats together. This also allows for random widths. Thus if
laying up a 4' wide panel, the nominal 2" wide pieces are added until
4' plus some fraction of an inch of over hang is reached. The wedge
is inserted and the edges compressed. What also happens, as the wedge
pressure is increased, the panel starts to buckle up. This is good
because the 1800 lbs/sq.ft. presses it flat to the sled and applies
more edge pressure. If the slats are not of uniform thickness, by
allowing the bag to press directly on the slats it pushed them flat to
the sled. Thus one side is flat, the other is somewhat irregular.
Laminates in press under vacuum (P5).
Taking this a step
further to get more production from a vacuum press, a frame press 24" high
can accommodate several sleds. The bottom of the top sled acts as a
caul and presses all the slats down. If the slats are not uniform in
thickness, then a mat needs to be placed on top of the slats and then
the next sled. The mat will compress to make up for varying
Check it out video