Page 94 - Materials Chemistry, Second Edition

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Sawing Cleaner Production 75
Sawing is the cutting of timber usually as near as possible to required size. If
wood is sawed across the grain it is called crosscutting, and if it is sawed paral-
lel to the grain it is called ripping. Sawing can be done with a portable manual
saw as in small workshops or with automated sawing machines in large factor-
ies and medium workshops. Sawing machines can be circular, band, scroll,
or radial.

Planing
Planing is the process by which the faces or planes of timber are made flat,
and usually perpendicular to each other. A planer is used for this purpose. In
large factories a power planer or jointer is used which consists of a set of
blades set on a rotating cutter head.

Sanding
Sanding is used to smooth the surface. In small workshops medium grit
paper (100–120 grit) is used for the purpose. Sanding is made along the grain
never against it. Some times the surface is wiped with a wet rag to cause the
surface fibers to swell and raise. A diluted solution of glue or resin is applied
with a rag to roughen raised grains. Then a finer grit paper is used to remove
raised fibers (200–250 grit). For large-scale production entities an automated
disk, belt, or roller machine is used. Sanding using different grades of grit paper
is used along many stages of the manufacturing process.

Assembly
Assembly of wooden parts can be done before or after the surface finishing
process. In small workshops furniture is usually assembled before finishing.
Assemblies in small workshops depend mainly on the use of glue and
nails. In larger factories interlocks are used. This gives the furniture an antique
essence. It is always recommended to use interlocks for high quality furni-
ture. Since iron nails contract and expand more than wood due to different
weather conditions climate differences will affect the nails more readily caus-
ing this type of assembly to weaken. Interlocks can be made out of wood
waste logs using a lathe.
Veneer is a thin layer applied to the furniture using glue and pressure.
Veneer is then sanded and sealed to pass through a staining process similar
to that of the painting process described next. The only difference is that a
polyester layer is not used in the staining process.

Finishing coating process
• Derosination: Because certain types of wood contain rosin (a natu-
rally occurring resin) which can interfere with the effectiveness of
certain finishes, a process known as derosination may be employed.