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Thread: I need to stiffen up a hollow cube

  1. #1
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    1,566

    I need to stiffen up a hollow cube

    I built a filter box, an evolution of the Comparetto Cube/ Corsi- Roesenthal box ( no idea who designed it first).

    My evolution I am calling "the Poindexter." Like many other wood stove owners I have a 20" box fan like this running on low in the hallway of my ranch style floorplan to gently waft cool air from the floor of the bedrooms down the hall towards the stove, sort of enabling warmer air from the stove to waft gently along the hallway ceiling. I end up with less temperature differential between the back bedroom and the stove room with the fan running.

    Here is the prototype, 1 fan, three filters, the remaining two sides of the cube are the cardboard front and back of the box the fan came in. Duct tape and sharp knife. No measuring, just tape it up and cut the cardboard to fit during assembly.

    20211016_215631[1].jpg

    It 'seems' to be working, I have two air quality meters on order, but there are two problems. One, it is not very rugged at all. Two, it would take up less space in the hallway if I could lift it off the floor a little bit so I have a filter on the bottom surface, and a blank (cardboard, plywood) on the left side as pictured, then scooch it up against the wall to the left. A plywood top would be good, I have found our cat napping on top of the pictured item twice already.

    So I have a plan. If I start with a 48x48 sheet of plywood I can make a floor big enough for the box fan to sit on, and the top, and a front upright between the top and bottom with a circle cutout the size of the fan blades, and a 20x20 blank to go on the left side that could be moved to the right side if I want to put it on the other side of the hallway.

    My thinking is to stack 1x2 furring strip in this shape (looking from above) for the columns at the back:

    20211019_130442[1].jpg

    So looking at those from the side there would be a face frame to duct tape a furnace filter to, and a resting surface for the back side of the filter to rest on.

    My current thinking is I could make an X brace between floor and ceiling at the back with more furring strip and that ought to be enough. It will cost me a tiny bit of airflow from the filter on the back wall, but I am also thinking it may not be enough. I want to be able to mount a handle near the center of gravity so I can carry it up and down stairs as needed.

    Thanks.

  2. #2
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    1,566
    The duct taped item in post one this thread is starting to shake itself apart. The fan torques up on the filter cube, lifting (as pictured) the bottom right corner of the fan off the carpet, and then gravity overcomes the torque and the fan drops back to the floor. I am not sure how long the build in post one is going to last, but probably less than the three months I am hoping for before I have to change the filters anyway.

    So I made the bigger more complex thing, like any fool can do. This one has been running about 24 hours now, 3/8 BB carcass, 1/4 BB for the fan shroud, double sticky weather stripping for the fan to sit on, a bunch of wood glue, furring strips. Couple coats of spray shellac. The two blank sides on this one are 3/8 bb plywood glued permanently to the framework.

    I don't love it, but it should work good in my wife's office, she only has room for it in a corner. I would sure like to come up with something simple and sturdy with a horizontal output. Something accessible to folks without a lot of shop tools trying to keep the kids healthy by keeping the air clean without spending a lot of dough.

    I will stop by the building store next to get some of the metal strapping they use as joist stiffeners for 2x10 on 24" centers. Those should be at least 26" and I should be able to tape them into the filters during assembly.
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