Stro's Flowhood Build



It all started when I acquired a bit of time off work, the spare time is few and far between these days so I took advantage. I was building some shelves and geeking out on some 3D software for fun and then that very same day, I went into doing sterile work inside the SAB, and that’s when in dawned on me; "I should build a flowhood!" And I will be the first to say. "It's about f'n time!" I am not quite sure how I have been doing this hobby for so long and not gotten around to it but the time had finally come and as shown above“there she blows!” Shown below, the oringinal 3D plans.



It’s an 18”X12” Laminar Flow Hood with an easy access top door for pre-filter replacement and blower access.
Let's start with the bread and butter, shall we? Das Holz yea? The wood! I opted for the 3/4” Birch, which is a bit more expensive than Pine but a quality ply. I purchased one 8’X4' piece and then cut it using a circular saw with the measurements shown below.
For the main box
2ea 24”X16” (top and bottom)
2ea 19 ½”X16" (sides 1 and 2)
1ea 24”X18” (back)
For the pre-filter box
1ea 13 ½”X15 ¼” (top)
2ea 12”X12” (sides 1 and 2)
3ea 13 ½”X12” (bottom piece and filter front)
3ea 12"X1" (filter inlet spacers)
Here are some dimensions and shop plans for you.


Then I started prepping with the orbital sander. Step down on the grit, 80, 120, 220, 320.

After that I hit it with a pre-stain conditioner, followed by the 1st coat of stain, I used a gloss pecan poly-shade, I let it dry over night, then hit it by hand block with 600 grit paper, then 00 steel wool, and then one more coat of poly shade and let dry.

The final results were look’n pretty good.


After this I started thinking about placing an order for a filter and blower before beginning assembly. I knew I was planning on using a 24"x18"x 5.8" HEPA purchased from FungiPerfecti which has a static pressure rating of 0.8” and using a pre-filter with an estimated static pressure rating of 0.2”. The next I needed to know is how many CFM I needed at my 1” of static pressure. Here is where it gets a little confusing; the goal is 100 lineal Feet Per Minute leaving the filter, which in other words means for every square foot you would want 100 CFM at this 1” of static pressure, it’s also recommended to leave a buffer addition of approximately 20% to your calculations, I doubt I got that much on this set up. The cubic feet for a 2’x1.5’ filter is 3 cubic feet. So we need 300 CFM at 1” static pressure. Time to start going through some blowers charts to find the best match. While looking around I noticed the charts tend to max out at .8”, so I opted for the Dayton 1TDT2 which pushes 360CFM@.8”SP. I read several builds where this worked out great with a 24X18 so I ordered it.
The exploded build with some dimensions depicted:

During assembly I did drill a lot of pilot holes to prevent cracking, for the trimming I ended up switching to finishing nails because it was becoming problematic. Depicted below I am starting with the back and the bottom and lining up the 1”X1” stops that will be put in place before assembly.
For the stops I used 1”X1” dowel square, I bought two 36” pieces for $3.50 each totally $7.00. Although not necessary I cut each end at the appropriate length at a 45-degree angle.

Continued with the two side pieces.
Lining it up with the filter again to make sure its snug.

An inside shot.
At this point I siliconed the inside of the currently assembled parts.
Started working on the handles, these ones were a pain


I set the top panel of the main box on and stacked the pre-filter box on to see how things would line up. Once I had everything set I marked it got ready to cut a hole in the top panel for the blower.

I did an on the spot measurement for the blower outlet and cut it out with the jig saw.

I started working the filter box cuts while I was at it. As a reminder the four pieces that make up the front of it are
2ea 13 1/2" X 12"
3 ea 12"X1"
Here is some 3D work with the corner dimensions of the 12X1's, the air inlet cuts, also looking down at the air induction body.


Started cutting and assembling.



A problem:

A solution:

After it dried and I trimmed the lip, I cut the 12"X24" pre-filter and tried it out, you can see it here slid in most of the way, it fit great.


It's time to attach the pre-filter box to the main one, I had to improvise on the screw placement, I marked it from the top and drilled small holes from the top to use as markers when working from the bottom.

Once set I installed the blower, it got a little bit tricky because of how far I need to too reach for the screws in such a confined space, but this connected series of extensions worked great.

Wiring it was super simple for the most part. Aside from the obvious depicted below, the positive (black wire) ran through the switch I was installing on the side of the box.

Although the switch gave me a hard time and I had to get creative to install it by drilling a large hole and adding a face plate, the ball jar cap concept turned out nicely and really suited the hood well.

Here is she is all wired up and ready to go.

The wire coming out of the back of the box, I used a rubber grommet for a clean finish.

Although I probably would of have kept working on the top at this point, it was time to call it a night so I installed the filter, applied silicone, weighted it, and let dry over night.




I added the trim to the filter front using general purpose pine corner guard, cost around $11.00 for an 8' piece, you should be able to pull off the entire hood with three of them if you know what you are doing but I honestly didn't do the math or worry about it too much. I was enjoying my self learning the cuts. The front is one of the only parts that didn't have finishing nails in it, secured only with wood glue, another reason I siliconed the outside edge of the filter. A bit of a pain during the drying process and I had to improvise yet again.


Finishing up the pre-filter box I installed the hinges, weather seal, and draw hasps. I weighted the top of the box while I installed the hinges and hasps for snug fit over the weather seal.






Testing her out.

From this point I started working on the edge guard trim, once I got started with it it took on a project life of its own and I had to learn things, get creative, and make custom cuts, I had fun with it.
Here are the majority of the materials needed for the build. Of course I am sure there are things you will need here there missing from the list.
1ea 8’X4’ ¾” Birch Plywood cut as follows
2ea 24”X16” (top and bottom)
2ea 19 ½”X16" (sides 1 and 2)
1ea 24”X18” (back)
1 13 ½”X15 ¼” (top)
2ea 12”X12” (sides 1 and 2)
3ea 13 ½”X12” (bottom piece and filter front)
2ea 1”X1”X36” dowel square
24"X18" HEPA filter
Dayton 1TDT2 Blower
1 1/4" wood screws
3/4" wood screws
Panel nails (finishing nails)
Edge Guard Trim
Hinges
Draw Hasps
Weather Striping

I don't have the exact cost of the build but it was somewhere upwards of $425. The fact that I was enjoying myself during the time and that a quality build was important from the beginning, it was too easy to spend more money than absolutely necessary. Nonetheless, it was all well worth the process and final product.
Enjoy
- Stro