Installation Guide

28
Basic Cementing Techniques
The two basic cementing techniques using unthickened
cements are:
1. The capillary action method.
2. The soak or dip joint method.
The soak or dip joint method is not recommended for
Plexiglas
®
MC acrylic sheet, because it dissolves
rather than softens the sheet.
To use the capillary action method, the parts must be closely
fitted, with no visible gaps. The parts to be cemented are either
unclamped or very lightly clamped together. The cement is
dispensed (from a hypodermic needle, eye dropper or similar
instrument) along the edge of the joint. Capillary action draws
the cement between the parts. The time for the joint to set
will
vary from two to five minutes (sometimes longer), depending
on
the solvent used and temperature and humidity conditions.
Figure 15 illustrates this method.
Do not flow or drip solvent cement on a flame-polished laser-cut,
strip-heated or dry-belt-sanded surface, since these conditions
show the maximum amount of fabrication stress possible in
plastic sheet. With Plexiglas
®
MC acrylic sheet, use a minimum
amount of solvent and pressure in the joint, since it is more readily
attacked by solvents, resulting in longer set times, lower joint
strength, whitening in the joint and increased risk of crazing
because the solvent takes longer to evaporate.
In the soak or dip method, the parts must also fit closely. One
of the parts is placed in a container holding a solvent cement
until the edge softens into a cushion. When the parts are
assembled, the cushion from the first part forms a cushion on
the other part by solvent action.
Masking may be required near the edges to be cemented, to
prevent excessive softening. The parts should be allowed to set
for 24 hours before handling. Figure 16 illustrates this method.
1. Machine pieces with sharp tools so the parts to be joined fit
without forcing or flexing. Do not polish edges to be cemented.
Apply masking if required.
2. Dip or soak the parts until the desired amount of cushion is
obtained.
Cutout
for part
Soak tank made from any material not affected by the solvent.
Tightly applied tapes such as 3M #670 or
equivalent may be used.
Masking may be required in this
area to prevent attack by the
solvent vapors.
Tank Cover
Solvent Level
Cushion
Solvent depth about 1" deep
Soak or Drip Cementing Techniques
Tank cover (made from
any material not
affected by solvent) to
minimize solvent
evaporation.
Support part on nails, wire
frame, inverted angle iron, etc.
FIGURE 16