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GrowFAQ : Getting started : Growroom design and
set-up

DIY: How can I build a compact hood with an intergrated
light trap?

Added by:
MarvinM92  Last edited by:
MarvinM92  Viewed: 967 times

Rated by 6 users:
9.67/10

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...

Last modified: 17:13 - Feb 22,
2003

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faq:1440 "DIY: How can I build a compact hood
with an intergrated light
trap?"