Cannabis Fact Contributed by: Teddy Bear
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
(Jade Tea Garden, Gumby, Vulcan, Super Tree Hugger, etc...) this
problem often popped up... How do you bend sheet metal
w/out a proper press brake? This methodology works like a dream
and requires only a few pieces of sdung wood...
Primary Tools:
נTin snips
נRivet gun
נSquare / Straightedge
נUtility knife
נDrill
נGood marker for layouts
Materials:
נSheet Metal - Picked up large sheet of decent gage sheet
for $8 at The HomeDeopt...
נHPS Light
נGlass Shield
נPlug and Wire
נPaint - White and Black - Use HIGH TEMPERATURE only...
(For BBQ grills/Engines/Radiators?)
נWeather Striping
נFoil Tape
נSdung 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 elevated 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 sdungs 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 sdung 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 and 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 elevated 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 elevated 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 sSuper Tree Huggering
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
נJoin 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...
נPaint assembly with flat white HIGH TEMPERATURE
paint...
נInstall the electronics (ballast, starter, power cord to
timer)...
*NOTE: For details on wiring a security light check
the "Lighting" folder in the Grow Fact'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...
נNow might be a good time to test your hood assembly!!!
Yeay...
Unit Assembly Installed
נThe 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...
נInstall 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...
נSeal 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
elevated 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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