Contributed by: MrE The
following are somewhat detailed instructions for
constructing a shielded hood/reflector with an
integrated light trap designed for a small cabinet... It
can certainly be scaled up for larger lights, but a 70w
HPS (Home Depot security light) was used here...
Final Product 
*Note: While researching on other
hoods/reflectors (Jackerspackle, Nimby, NGB, Tick,
etc...) this problem often popped up... How do you bend
sheet metal w/out a proper press brake? This method
works like a dream and requires only a few pieces of
scrap wood...
Primary Tools:
Tin snips
Rivet gun
Square /
Straightedge
Utility knife
Drill
Good
marker for layouts
Materials:
Sheet Metal - Picked up large sheet of decent gage sheet
for $8 at The HomeDeopt...
HPS Light
Glass
Shield
Plug and Wire
Paint - White &
Black - Use HIGH TEMPERATURE only... (For BBQ
grills/Engines/Radiators?)
Weather Striping
Foil Tape
Scrap Wood
Layout
*Note: The dimensions are for a 70w HPS
bulb... If you are building this to use with another
size bulb you must alter the dimensions accordingly...
So scale/adjust to suit other bulb wattages...
Illustration for the Light Trap's
Layout...
Illustration for the Hood's Layout...
The Light Trap Subassembly
Start out by transferring the dimensions from
the layout to the sheet metal with a magic marker... Try
to be very accurate and definitely use a square...
In this image you'll see A) the sketch on
cardboard in the background used to plan hood to fit in
the small filing cab, B) the dimensioned flat pattern
layout on paper, C) a section of sheet metal with the
layout already transferred...
The pattern is then cut with tin snips and
"scored" for bending... The scoring is important to get
a nice crisp bend... Use the utility knife, and make
like you?re going to cut on a "fold line" and take a few
passes... The score should be on the outside of the
bend...
Folding technique - using 3 scraps of plywood...
Two sheets sandwich the section of sheet metal that will
be stationary during the bend... The third sheet is
placed as shown below the section to be bent, and
butting up against the bottom of the sandwich, meeting
right on the bend line... Be careful not to get any of
the 3rd sheet below a section not to be bent yet...
While standing on the "sandwich", pull the 3rd
sheet up with confidence... The resulting bend is shown
and is very crisp, accurate, and straight due to the
score... Don't bend completely; just as shown... The
remaining degrees in the bend will be completed by hand
later...
Continue bending... Here, you'll stand where the
hammer is sitting...
A narrower piece of scrap wood is used here for
easier bending...
The final bends are made by hand - simply grip
the sheet metal with the V in the fold facing your palms
and squeeze... It will bend easily, and again, the score
will help here... A bottom view of fully folded trap...
Note that the tabs have been drilled and
riveted... This would be a good time to seal the seams
with high temperature foil tape... I didn?t do this at
first (I was trying for 100% metal unit) and ended up
with tiny light leaks, so I had to add the tape later...
With the airflow through the hood it runs fairly cool
anyway... A top view...
The Hood & Insert Subassembly
Transfer the dimensions from the layout to the
sheet metal with a magic marker... Again, try to be very
accurate and definitely use a square...
The
pattern is then cut out with tin snips and scored for
bending... Remember, the scoring is important to get a
nice crisp bend... Here is the scored and cut sheet
ready for folding...
Take note of this image... It is a rectangular
section used as an insert, bent into a V shape, for
reflecting light above the bulb... This is an important
element of the design... Hopefully you can see the
detail of the scored lines here... BTW- the fancy Kett
Power Snips were borrowed from AF and worked well, but
hand snips work just fine, and are required for getting
into the little corners anyway...
Image shows the hood and V Insert folded... The
bar on the top is used to secure a 90-degree bracket on
the inside for holding the light fixture (note the wires
sticking out)... It was salvaged from the security light
housing...
Rivet the V Insert in place... You can see the
90-degree light bracket on the left... The rivet gun has
a fancy swivel head that was more useful than expected,
but any one should work ok just fine...
Finishing Up
Join the two
sub-assemblies together... Used a small piece of sheet
metal at back end (end of bulb pointing toward it), and
fashioned another piece for the end closest you in the
picture...
Paint assembly with flat white HIGH
TEMPERATURE paint...
Install the electronics
(ballast, starter, power cord to timer)...
*NOTE: For details on wiring a security light
check the "Lighting" folder in the Grow FAQ's...
The
ballast is shown up front here and worked fine for 1st
grow, but have since relocated the ballast to the back
of the unit where the exit is located, thought it would
add a slight bit less total heat, maybe, and no longer
use carbon scrubber cartridge...
Looking at the
final image at the bottom, you can see the exit with
weather stripping around it that mates to exhaust port
in cabinet... It is in here that the ballast is now
located... Secured ballast with a sheet metal strap... I
had a bit of issue with ballast humming... Wedging a
metal shim under the ballast to make it snugger
eliminated the vibration and it's practically silent
now, even at startup...
Now might be a good
time to test your hood assembly!!! Yeay...
Unit Assembly Installed
The
remaining triangular shaped space on right side is used
for power junction box and in front of that the timer...
Keep all electronics upstairs and away from fluids... No
separate utility room need for this cab!! There is an
air space above the hood...
Install glass
shield... Tempered glass is best but I used regular 1/8"
glass; as it's fairly small wattage and little stress is
placed on it... A gap of 3/4" or so is left at far end
for air to enter, pass across bulb, and then flow out
hood and over ballast on way out of box... You might
note the two channels bent along either side of hood for
glass to slide in... Add another inch to the glass width
to account for channel it slides into...
Seal
the front of the assembly... Used a material called "
Reflectix". Version 1 of the cab had Reflectix on the
walls and door, and when closed sealed off the front...
Now I?m using Mylar, so it?s shown for current setup...
Light On!
The camera was
placed on the floor of cab for this shot... Each image
is simply a different exposure... The left image gives a
good idea of where most of the light goes... It is said
little light is emitted from end of bulb, and this
picture makes that fairly clear... The right image shows
the imbalance in my light distribution a bit more
clearly, due to about a 3/16" misalignment of the bulb
over the V Insert... Will tweak that before next grow
when glass is removed for cleaning - however, it does
demonstrate how important the V Insert is and also that
accuracy does matter for some parts of the setup...
Carbon Scrubber Insert
Abandoned this for now...
This little module
was made with a flouro light fixture grill cut to
triangles and stacked and glued to achieve about 4"
length... Channels are filled with activated carbon for
scrubbing odors... It was inserted into back of cab
through the opening, and then slid in... It caused too
much static pressure for the single fan being used... (I
had to go with active intake) So now use stacked
scrubber modules on back of cab - oh well, so much for
100% containment with-in the little cab - still
stealthy...
Buds in First Grow
Just a
shot to show that this light and tiny cab will produce
some decent smoke... Goal is to achieve 2oz in this cab,
which seems do-able...
Conclusion
Well, there you
have it, an air-cooled hood assembly with integral light
trap - all for less than $100... This took me a full day
and well into the night to design and build, however,
the design part was probably 80% of the work... Also
doesn't count a day of searching OG to see what others
had done... Could probably build one of these in an
afternoon now - or maybe just a bit longer than the time
is took to prepare this post!
Works for me! On third grow with this setup and
it performs well... The temperature increase is about 6
to 7 degrees above ambient... More fan power should
bring this down; the flow is probably a bit low now
(only 1 Rotron fan on intake at this point, another tiny
one below glass in corner for circulation)... An active
exhaust would be an improvement, as there isn't airflow
through the hood when the door is removed... Didn't have
fans that would fit at the time this was built... Have
since picked up some smaller Rotron DC fans that will be
used to add an active element to the exhaust at some
point... I'd recommend this from the start...
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