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Here I will go through my flowhood build with you. It was inspired by squid and mz. I basically decided I'd walk into one store and get everything I need in one shot, no driving all over the place. I thought up my build walking around home depot. I knew from ology what wood to use and what type of prefilter. I didn't have it all planned out to a T, driving all over the country looking for this part or that. My goal was one store visit and do my build, as inexpensive as possible with the best quality. I could have spent more money for even higher quality, but the FH is a tool. Like my dewalt. Rugged, tough, dependable. My hood is not an AR, it's an AK:) this tek is not super duper precise, I was too busy building my hood to work even harder writing a tek so exacting, but you can do it too. A little ingenuity will be required to copy it. I dont have every minute detail for you, but I will give you plenty of info and all the important stuff. Let's begin shall we? Supplies. 2'x2'x12" hepa filter, carpet blower, I used a CFM PRO 3000x. Home depot supplies, 4 2'x4' sheets of 3/4" sanded plywood, good edges and not warped. A tube or two of some type of sealing stuff, I used loctite brand 2 in 1 sealer/adhesive. Screws, I got ones similar to sheetrock screws but better metal and it came with a torx bit in the box for them. They were probably 2 1/2" or so. Make sure they are long enough to go through the 3/4" ply and get a good bite into the other piece. L brackets, they were maybe 2" on each side with 2 holes in each side. I used 8 of them, 2 four packs. Don't use the screws that come with them, they are not good enough. You will need 32 #10 screws. They are strong enough to use with the L brackets. Get some silicone for sealing the pre filter in place, and to seal the hepa to the wood. Don't use strong adhesive for those parts or you'll never get it back apart. TOOLS- T-square, yardstick, circular saw, jigsaw, drill, 1/8" drill bit, belt sander, pen, marker, bit for whatever screws you're using. Let's move along now. The hepa filter is 24"x24" from the front with the flange. Behind the flange, the filter housing is 22 1/2" square. Take one of your pieces of plywood, measure 24" from the end with your t-square and Mark a line. So your cutting 24" off the end. Put an x on the side your using so you don't mess up. They sell them as 2'x4' but they are not, they are a tad bit smaller. It's so you have to buy more wood. If you measure 24" in from both ends the marks won't match up. After you cut your piece, lean the hepa forward and slide the piece under up against the gasket. It should reach all the way to both edges of the flange perfectly, if no try turning it. If you made the cut right it will fit one way. Now let the filter lean back and it will rest on the wood and stand up straight. Now take a new piece and make the same cut to make the top piece. It should be 24"wide flush with the flange. Now, the side pieces need to be 22 1/2" tall to fit between the top and bottom piece. When you cut them, cut it where the line you marked is still there, right on the end. Do both sides like this. This will allow the filter to be removed later, rather than it being tight in there, permanent lol. Now, make sure all the four sides meet the gasket together, that they are flush from the front. This is the most important part of making the box, making sure the gasket will meet the wood evenly all the way around. You can do all your adjustment when adding the back wall. Use a ruler to figure out how far in to measure for your pilot holes so that they go straight down into the middle of the plywood. Use the ruler to make little pen marks for where to drill your pilot holes. Go on the ends first and hold it so it's flush and perfect. DON'T DRILL INTO YOUR FINGER! Put in a screw. Then do the other end the same way. Then do the other side the same way. (Your drilling down through the top piece into the "walls". Now that you have the four corners screwed in nice and perfect it's held together. Now use your ruler and Mark your pilot holes down both sides. Don't be stingy with the screws, they give it much strength and pull it all flush. Now, lift the 3 pieces of wood you just screwed together off of the filter. Don't worry it'll be rigid as hell. Flip it over and put the filter back in place now you will do the same to the "bottom". Take your time and make sure your pilot holes are straight and that they go right into the middle of the "wall" piece. Start with the far ends first so it's lined up for ya and make sure all the pieces that are going to be up against the gasket are flush and even with each other. The "front" is important! The back can be tinkered with in the end. Now you have the four sided box built. Now we will attach the blower fan. Make sure the "up" side of the box is facing up. Put arrows in marker. Also, when you built the box around the filter, mark which side is up on the box and the filter flange. Put arrows facing each other. So you can get it back in there no problem. Ok, back to the fan. Put the fan on top of the box as far back as possible while still leaving room for the L brackets, so the brackets don't hang off the back. Use something to prop the weight of the fan so the spout sits flush on the wood. Trace around the spout with a sharpie. Now take down the fan and set it on the ground facing up if you can. Take a piece of paper. I taped two notebook sheets together. Now use tape and tape the paper taught over the spout. Use a marker to trace the INSIDE of the spout. Now remove the paper and cut out the "template". Now go to the box. Center the template in the outline of the spout you traced before. I taped it down with packing tape completely, flat and smooth. I didn't have a big enough drill bit too start the jigsaw cut so I used the circular saw. Pull back the guard, pull the trigger, and go straight down into the wood. Do it along one of the long edges. Now your jigsaw blade can get in there. Cut around the template that you taped down. It's not exact science. Just don't make the hole too big. Now prop up the fan again like before with the spout in the spot you traced. Now is where you will position the L brackets and use a marker to mark where you must drill pilot holes. The weight of the fan wants to lean forward, so I made the back edge allot stronger than the front. Drill your pilot holes in the wood and in the spout of the fan. A picture is worth a thousand words check it out, Use your #10 screws for this part. With everything marked and pilot holes drilled, mount 2 brackets to the front of the fan spout on two sides, and 2 more on the back. You'll want a hand from someone for this. Get your sealer, silicone, whatever goop you chose and put a healthy bead on the wood where the spout will contact it. Don't use a drill for this part you'll strip the holes out. not good. Use a screwdriver or nut driver. Have your helper help you lower the blower into position carefully. Don't ruin the seal you put down and don't make a mess. Once it's down enough drop a screw in one hole of each bracket into the wood. Go all the way around. Still supporting the weight, put screws snug in every hole you drilled. There should be 4 screws per bracket. I used 5 brackets in back and 3 in front. DON'T STRIP OUT THE HOLES!!! Now use a bathroom carpet on the ground for protection and lean the whole box forward on its front. We are now putting on the back cover. If the walls are uneven sand down the tallest one if you gotta. Line it all up, drill good pilot holes and screw it on. Now lean it back so it's sitting upright. Sweep out all the dirt and dust from in the box. Now the pre filter. I used a honeywell from home depot. It was 24"x24". Too big for the hole. Measure how deep your hepa will go in the box from the gasket back. Make marks inside the box so you put the pre filter back far enough that the hepa won't knock it out of place. I'll be honest. This part was GEETO LOL. but it did the job. It was starting to rain. I folded back the edges of the pre filter in a rough manner. I cursed at it and got it in there. Then I used my caulk gun and just globbed the crap out of it around the edges till it would dry and not leak. Not pretty, but functional, and replaceable. I didn't put it in with some crazy adhesive. Just caulk. I can get it back out if i need to. (NOTE: before putting in the pre filter I went around all the inside edges with caulk. "Airtight".) Remember where you made the marks for how deep the hepa would go in the box? Use a putty knife or something to make sure the caulk in the corners is minimal as possible. You don't want the caulk to make it impossible to get the hepa in. Behind that, glop it on if you like. No one will see it and it's not hurting anything. I ran my finger down all the edges. Be excited at this point. Lean your flowhood back so the front is facing up. Put a light bed of silicone around the wood where it will mate with the filter. Get someone to help you and lower the hepa down into its place. Now I looked real hard for a cool mounting hardware for the hepa, you know, "squid clips". I found NOTHING! I bought some metal stripping with the holes. Pretty sad that all I could find. But I wound up just drilling pilot holes through the flange on all four sides and just screwed it right down. Came out real nice. Any part on it can be replaced or serviced. The only way it could be better would be if it weighed 100 lbs less lol. I started at 12:45pm and it was complete at 7pm. I retract my previous statement. SHE'S A BENTLEY! Gorgeous. Thanks to squid, MZ, and MT for making it happen, and most of all my old man. He's a legendary mechanic. I'll put up some better pics of the finished product as soon as I can take some. I think the way the blower is mounted is PURDY:)