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Discussion Starter · #1 ·
I am building an air filter box frame which will mount a total of 4 20x20x1 filters. Each filter will be mounted on one of the 4 sides of the box; the top and bottom of the box will have supporting plywood plates. One side will also have a box fan mounted on it. Right behind the fan, the filter will be of a lower Merv rating in order to allow sufficient air passage.
The frame was cut with a cnc router, and the pieces fit together really well. They are 3/8 MDF to keep it light.
I am not sure how to square it, given that it's such a big box. The pieces all snap together tightly, so clamping the box is not necessary.
This is a prototype for a large room almost hepa air cleaner, featuring 3 Merv 13 filters, one Merv 8 with an easy to attach box fan in front. It will also have casters on the bottom.
Where I live, we can get a month of smoke from forest fires. If this works well, I may want to build them for the community. The assembly method, therefore, should be almost foolproof.
Once it's built and tested, I'll be happy to send anyone interested my dxf files.
Given the cost of air filters, if this design works, the total cost will be 1/5 of a commercial unit.
I now need some advice on squaring it.
thanks
tony
 

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I'm assuming it has a square bottom already so that keeps the bottom pieces aligned. You'll need a top on it too otherwise some of the air will bypass the filters going in and out. The easiest top to get on and off would be one with a small lip that sticks over the edges. If yo add strips (cleats) the dimensions of the inside of the box then that will will keep the top square while your glue is drying and help keep it from racking while you move it.
 
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Are you planning to glue and square up in some sort of sequence, or are you wanting to do all four sides in one go?
 

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The bottom, if cut square should help hold it square. The other factor would be how square the edges are of the pieces you're assembling. Since it was cut on a CNC, are the edges cut exactly 90 to the surface? If not, getting and holding it square during glue up will be challenging.

So I suggest you use some 90 degree L shaped blocks clamped into the corners to hold it square. I personally would cut an exact size, square piece of ply or mdf that fits the inside dimension, to brace the framework on the bottom of the structure to set that square. If the bottom is solid already, that will hold the framework square on the bottom and you'll only need the L brackets to hold the top. You will only be able so do a little adjusting for any racking since the MDF cannot be torqued the way you can with real word. Twist it much and it will fail.

If you drop this MDF structure, it will likely fail. You could reinforce it with some light weight aluminum L shaped extrusions. I would have made it from solid wood (like interlocking face frames) or ply.

I made a simple box fan filter many years ago and used a commercial filter holder like the one in homes. The casing is ply, assembled with pocket holes. The filter holder holds everything square. I took the box fan apart and installed it in the box. The other side had a simple vent cover. I installed the 3 position switch on the bottom so I could reach it to turn it on. The box fan never had the power to move much air. It would have required a much higher hp fan to be effective, something you might consider purchasing, perhaps a used commercial unit.

Four filters of any quality is going to cost $40-$50 a set to replace. I found a WEN hanging filter on sale for $99 at WalMart online, picked it up at the local store. It has a remote, plus 3 power levels, and a timed shut off. Works far better and is more convenient to use than my home made gadget. When you hang any filter of this type, install it near a wall so you get circulation going in the shop.

I spent a lot of money trying to save money on dust collection, all to have a shop full of sawdust and fine particles. I finally realized that none of the cheap-o solutions really worked very well. So I bought a couple of Harbor Freight DC units (about $160 each on sale with a coupon), added a Wynn canister filter to the one I had in my shop (Now sits outside, the other has a bag, but gets rolled outside for use). Have two of the WEN filters, one in both shop areas. Sawdust is no longer an issue. Wear a ventilated filtered mask (Rokler), and when not cutting, wear medical type mask. Looking back, all my home made solutions didn't really work well. The commercial units work very well, and actually cost me about as much as all my ineffective efforts combines. False economy on my part.

After reading an OSHA report on home shop dust pollution, I realized the risks of COPD and other lung problems were not worth trying to save a buck. Serious dust collection may well be the most important tool you have in your shop.
 

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David
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Welcome to the forum, Tony! Add your first name to your profile so it clears the N/a in the side panel. Adding your location in your profile helps, too.

This is your second post in 7 years and the first one was about a trim router base for mounting in a table and this one involves CNC - things have changed for you! We'd love to see your shop, tools, other projects, etc. and we do like photos. :grin:

David
 

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Discussion Starter · #7 ·
The bottom, if cut square should help hold it square. The other factor would be how square the edges are of the pieces you're assembling. Since it was cut on a CNC, are the edges cut exactly 90 to the surface? If not, getting and holding it square during glue up will be challenging.

So I suggest you use some 90 degree L shaped blocks clamped into the corners to hold it square. I personally would cut an exact size, square piece of ply or mdf that fits the inside dimension, to brace the framework on the bottom of the structure to set that square. If the bottom is solid already, that will hold the framework square on the bottom and you'll only need the L brackets to hold the top. You will only be able so do a little adjusting for any racking since the MDF cannot be torqued the way you can with real word. Twist it much and it will fail.

If you drop this MDF structure, it will likely fail. You could reinforce it with some light weight aluminum L shaped extrusions. I would have made it from solid wood (like interlocking face frames) or ply.

I made a simple box fan filter many years ago and used a commercial filter holder like the one in homes. The casing is ply, assembled with pocket holes. The filter holder holds everything square. I took the box fan apart and installed it in the box. The other side had a simple vent cover. I installed the 3 position switch on the bottom so I could reach it to turn it on. The box fan never had the power to move much air. It would have required a much higher hp fan to be effective, something you might consider purchasing, perhaps a used commercial unit.

Four filters of any quality is going to cost $40-$50 a set to replace. I found a WEN hanging filter on sale for $99 at WalMart online, picked it up at the local store. It has a remote, plus 3 power levels, and a timed shut off. Works far better and is more convenient to use than my home made gadget. When you hang any filter of this type, install it near a wall so you get circulation going in the shop.

I spent a lot of money trying to save money on dust collection, all to have a shop full of sawdust and fine particles. I finally realized that none of the cheap-o solutions really worked very well. So I bought a couple of Harbor Freight DC units (about $160 each on sale with a coupon), added a Wynn canister filter to the one I had in my shop (Now sits outside, the other has a bag, but gets rolled outside for use). Have two of the WEN filters, one in both shop areas. Sawdust is no longer an issue. Wear a ventilated filtered mask (Rokler), and when not cutting, wear medical type mask. Looking back, all my home made solutions didn't really work well. The commercial units work very well, and actually cost me about as much as all my ineffective efforts combines. False economy on my part.

After reading an OSHA report on home shop dust pollution, I realized the risks of COPD and other lung problems were not worth trying to save a buck. Serious dust collection may well be the most important tool you have in your shop.
The fact is that the shop filters that you describe do not work very well with .3 micron fine particle dust, the ones that will most likely kill you, since the lungs cannot adequately filter them.
The best filters are Hepa, and it's rare to find a Hepa shop filter.
The box I am building will go into a living room, so it needs to look nice. Once the top and bottom are sealed, 3 merv 13 and one merv 8 filter will provide good flow and air cleaning.
tony
 

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Tony your drawing shows a lattice work on each side. If that is actually part of the design and not just shading in the drawing then that will keep the box square and rigid once your glue sets. I have some home made jigs that I clamp on the inside corners of things I glue together like that. If you want to see them I can post a picture later.
 
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