Transcript Finishing Greyfoam

Finishing Greyfoam
Putty Priming
 It is advisable to rub a thin layer of putty on the
prototype part before sanding
Fill up the microscopic cells on the greyfoam surface
Fill up the unevenness, holes, cracks and other surface
defects which are difficult to spot
Act as a marker so that in subsequent sanding, it is easy
to visualise which areas had been sanded
 Blow the model clean and dry before rubbing
putty
Sanding
 Sandpaper is a form of paper where an abrasive
material has been fixed to its surface; it is part of
the "coated abrasives" family of abrasive
products
 Used to remove small amounts of material from
surfaces, either to make them smoother
(painting and wood finishing), to remove a layer
of material (e.g. old paint), or sometimes to
make the surface rougher (e.g. as a preparation
to gluing)
 Waterproof or wet/dry sandpapers use a resin
bond and a waterproof backing
Adapted from: http://en.wikipedia.org/wiki/Sandpaper
Grit Size
 Grit size refers to the size of
the particles of abrading
materials embedded in the
sandpaper
 ISO 6344 is an international
standard covering the
materials sizes and tests
regarding sandpaper and other
similar coated abrasives. It has
three parts:
 ISO 6344-1:1998: Coated
abrasives, sizes and tests
 ISO 6344-2:1998: Macrogrit,
P12 to P220
 ISO 6344-3:1998: Microgrit,
P240 to P2500
Grit Designation
Material removal
Sanding finishes
Final sanding before painting
Sanding finishes between paint coats
Finishes before buffing
Final sanding before buffing
ISO/FEPA Grit designation
Average particle diameter
P60
0.269 mm
P80
0.201 mm
P100
0.162 mm
P120
0.125 mm
P150
0.1 mm
P180
0.082 mm
P220
0.068 mm
P240
58.5 µm
P360
40.5 µm
P400
35 µm
P600
25.8 µm
P800
21.8 µm
P1000
18.3 µm
P1200
15.3 µm
P1500
12.6 µm
P2000
10.3 µm
P2500
8.4 µm
Material removal
 Use #60 to #100 for
material removal
 Use a rigid sanding block
whenever possible
 Wrap the paper around
half-round or round
sanding-block to shape
concave surfaces
 Dry or wet sand
 Use the hand to feel the
surfaces
 Change sand-paper
frequently
General Sanding Rules
Face by face
From large face to small
From flat face to pronounce
Keep small protrusion and fillets
untouched
Putty Priming
 After the first putty priming and sanding, there
are usually over-sand areas that reveal the
greyfoam surface
 The area must be covered, otherwise it is not
possible to achieve a even, glossy spray
painting finish
 Lightly sand down the over-sand areas, rub
putty on them and sand them
 Repeat the process until the entire greyfoam
model is covered by putty
Spray Priming
It is advisable to spray a thin base-coat on
the foam model before sanding finishes
Give the part an even colour, reveal the
unevenness, holes, cracks and other surface
defects which are difficult to spot
Act as a marker so that in subsequent sanding,
it is easy to visualise which areas had been
sanded
Reveal contaminations such as uncured putty
or ink on the part
Sanding finishes
 Change to #200 - #400
paper
 The base-coat will be
removed gradually to
reveal body material
 The target is to ‘replace’
previous coarse
sandpaper strokes with
finer strokes
 The progress will be fast
at the beginning and will
slow down when the
contact surface area
increase
Progressive Sanding
 A: Thoroughly sanded
away all previous
strokes
 B: Leave a trace of
previous strokes
 C: Change sandpaper
pre-maturely
 D: Use finish sanding
to ratify unevenness
of C
A
B
C
D