How-
Do you design your own printed circuit
layouts? That being the case, you need a
good light box. This one is cheap, easy
on the eyes and easy to build.
By LEO SIMPSON
At SILICON CHIP we needed a
good light box. We design our
printed circuit boards using Bishop
tapes so we needed a light box for
that. And we needed a light box for
checking our wiring and overlay
diagrams and for marking up all the
photographs for page layouts.
When we came to look at commercially available light boxes though,
there were few that met our
requirements.
There were plenty of large commercial units, intended for use in
photocomposing rooms and so on
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SILICON CHIP
and some intended for doctors' and
dentists' surgeries, but few that
were reasonably compact and cool
and comfortable to work on. None
were cheap.
Most, if not all, used frosted float
glass as the working surface. We
did not want these. Glass light
boxes often break and therefore
can be a real hazard to anyone
working with them. Frosted glass is
expensive and inconvenient to
replace too, so that was another
reason not to use it.
Hence, we decided to design and
build our own. We are presenting
the details here for anyone who
needs a similar unit and who is able
to handle a saw and screwdriver.
The total cost is less than $70, if
you buy all new materials.
Essentially, all that is required is
a suitably shaped box, painted
white inside and fitted with an 18
or 20 watt fluorescent light batten.
On top is mounted a sheet of white
translucent Perspex. And that is all
there is to it.
·
We even saved ourselves the
trouble of painting it by using white
Melamine-coated particle board,
16mm thick. This was cut to size,
screwed together and the job was
half done. We spent more time
shopping for the materials than actually putting it together.
To make it easy to work on, particularly if you are taping up a
printed board design, we made the
box with a sloping top, angled at
15° to the horizontal. At the front ,
to build a light box
the box tapers down to 38mm, so it
is quite comfortable to work on.
Tools required
You can get by with the very
minimum of tools for this project. In
fact you could manage the whole
job using hand tools. To make it
easier though, you will need an
electric drill and a circular saw,
preferably with a tungsten-carbide
tipped blade.
The assembly process consists of
cutting the Melamine-surfaced particle board to size, drilling the holes
for the screws, power cord entry
and ventilators and then simply
screwing it together. Glueing the
box together is not practical, since
the Melamine surfaces won't take
glue.
The first task is cut the various
pieces to size.
We dimensioned the box to suit a
standard 18 or 20 watt fluorescent
batten (batten is the term used to
describe the whole fitting, including
the tube) with a few millimetres
clearance at each end. Just to be
sure though, measure your batten
before you mark up the sheet for
cutting it would be most
frustrating to find you had made
the box too small.
The top edges of the front and
back pieces of the box should be
chamfered to match the 15° slope
of the sides. This is easily achieved
by setting the baseplate of the circular saw to the correct 15°
setting.
With care in your saw work, all
the pieces should fit together
squarely with little need for work
with a plane or rasp.
To ensure you achieve straight
cuts, use a straight edge as a guide
for your circular saw. The idea is to
clamp a thin straight-edged length
of timber to the particle board and
use it as a guide for the saw.
Don't forget to drill the various
holes for the power cord and ventilation. We used kitchen cupboard
vents which fit in a 28mm (actually
1-1/8 inch) hole. You will need a
hole saw or a Speedibore (an auger
18W FLUORESCENT LIGHT BATTEN BOLTED TO REAR »F
- - - - BOX WITH TWO 5mm DIA. x 35mm SCREWS AND NUTS.
SPACE BATTEN FROM REAR OF BOX BY ONE NUT THICKNESS.
HOLES A: 28mm DIA. TO ACCEPT CUPBOARD VENTILATORS
8: 10mm DIA. MAINS CORD ENTRY
C: 6mm DIA.
REAR 130x613
A
i
/
--1
BASE 312x613
i
130
J
CHAMFER TOP EDGES OF FRONT AND
REAR TO SAME ANGLE AS SIDES (15').
ASSEMBLE BOX WITH 40mm COUNTERSUNK
PARTICLE BOARD SCREWS. COVER SCREW HEADS
WITH DRESS CAPS.
MATERIAL: 16mm PARTICLE BOARD COATED WITH WHITE
MELAMIME ON BOTH SIDES. COVER EXPOSED EDGES WITH IRON-ON
EDGE STRIP.
COVER TOP OF BOX WITH 360x645 PIECE OF WHITE TRANSLUCENT
5mm ACRYLIC SHEET.
DIMENSIONS IN MILLIMETRES
LIGHT BOX
4
rv
38
Fig.1: we made our light box from 16mm-thick Melamime-coated particle board. The dimensions shown suit a standard
20W fluorescent batten but we suggest that you check the length of your batten before marking the sheet for cutting.
MARCH 1988
61
The fluorescent batten is fitted to the rear of the case to give an even spread
of light. Kitchen cupboard vents are used to cover the ventilation holes.
bit made for electric drills) to drill
these holes. When drilling these
holes, drill through until the bit just
breaks through the surface and
then finish the hole by drilling
through from the other side. This
stops you making a mess of the hole
and possibly tearing the Melamine
surface.
Finish off the sawn surfaces with
a rasp or sanding block before going to the next step, which is to
make the rightangle butt joints to
assemble the box.
The various sections are then
screwed together. We used Chipboard screws (Bg x 40mm, countersunk, made by W.A. Deutscher)
which have a coarse thread for
good holding power. Underneath
each screw head we placed the
countersunk plastic washer for a
white Snap Cap (decorative screw
caps made by Furnco ).
Alternatively, you can use Furnco Directors, which are particle
board screws which are supplied
with their own decorative caps.
Either way, there is no need to
coutertsink the screw heads into
the particle board.
We used fourteen screws (and
decorative caps) to assemble the
box.
To finish off all the exposed
edges of the particle board, use an
iron-on Melamine edging tape
(Armaflex-GL) and then trim to fit
using a sharp utility knife.
Now fit four rubber feet to the
underside of the box so that it does
not scratch or move around on the
table.
The next step is to fit the Perspex
top. Assuming that you have made
the box to the same size as our
drawing, the Perspex sheet should
be 360 x 645mm. We used some
3mm thick sheet we had on hand
but we suggest 4.5mm material as a
better choice as it will be more
rigid. You can get Perspex cut to
size from glass suppliers or you can
go to a specialist outlet such as
Cadillac Plastics in Sydney.
We attached the Perspex to be
top of the box using four countersunk head self tappers, 20mm long.
Drill and countersink the screw
holes before you remove the protective paper coating from both sides
of the Perspex.
Having fitted the Perspex,
remove it again so the fluorescent
light fitting can be installed.
Remove the tube and the top cover
from the batten and place it in the
box as shown. Mark the positions of
the mounting holes at both ends and
drill the box for 5mm diameter
Close-up view of the batten wiring. The mains cord should be anchored with a
clamp and its leads connected to the 3-way terminal block.
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SILICON CHIP
screws. Before securing the batten,
fit the cord entry hole with a junction box grommet.
Secure the fluorescent batten
with two 5mm screws and nuts,
with one nut used on each screw to
space the batten away from the
rear surface of the box.
You may think that a more even
spread of illumination could be obtained by moving the batten more
towards the centre-line of the box
but we found that it gives a hot
bright strip across the middle
which is unsatisfactory.
Now connect a 3-core mains
power cord fitted with a 3-pin plug.
These battens are fitted internally
with a 3-way insulated terminal
block for this purpose. The centre
terminal is connected to the earth
wire. The cord should also be anchored with a clamp.
Now the cover and tube can be
fitted to the batten and power applied to test it. We didn't bother to
fit a mains switch on the box, by the
way, as it seemed superfluous.
Now fit the snap vents. Of course
you don't really have to fit these but
the vent holes look a bit grotty
without them. You could also fit a
handle to each end, to make it
easier to lift.
And that completes the light box.
Let there be light.
~
LIST OF MATERIALS
1 sheet of 1 6mm Melamine
surfaced particle board
1 18-watt fluorescent batten,
including tube
1 3-core power flex and 3-pin
plug
1 4 40mm x 8 gauge Chipboard
screws (or Furnco Directors)
1 4 Furnco white Snap Caps
size 8/8 (not necessary if
Furnco Directors are used)
4 20mm x 1 0 gauge
countersunk head selftapping screws
·
4 rubber feet
2 5mm 20mm long screws,
with nuts and washers
5 kitchen cupboard vents
1 sheet of white 4.5mm or
6mm Perspex, 360 x
645mm
Miscellaneous
Iron-on Melamine edging tape
(Armaflex G-L)
