Often times it takes a bad situation for you to make some necessary corrective changes. This is definitely one of them. While I’ve had the intentions of making an air cleaner for my shop for a while now it wasn’t until I got yet another sinus infection that I decided to take greater measure in regards to cleaning the air in my shop. My body definitely doesn’t like walnut dust and has no problem letting me know. I already installed a HEPA upgrade kit for my dust collector and today I’m making a mobile ambient air cleaner cart to clean the shop while I work.
DIY air cleaners are not a new topic. People have been making them for quite some time. All it takes is a decent blower motor to move a lot of air and some good filters. It doesn’t make much sense to make an air cleaner if you’re going to use low rated filters that won’t get the small, dangerous particles.
To move the air I’m using is an old furnace blower motor that I picked up from Shawn Stone. After taking the motor out of the housing I found the wiring diagram, hooked it up for the slowest speed, and tested it in both free air and again with filtered restrictions. The amperage draw during theses tests was on par with the rating on the motor label so I was good to go for a fan source.
Filters can be expensive. My original intention was to go to my local home center and buy four of their best filters. The cost ended up being $85.56 with sales tax and the filters didn’t have a MERV filtration level listed on them so I passed on getting them there. I ended up getting a box of six MERV 13 filters off Amazon.com shipped overnight to my house for $35 less than the price where I live. So that’s the route I went.
Next up was to decide where to put it in the shop. My original plan was to make this cart for my grinder but I accidentally found out that it fits below my drill press very well. The next best thing was to replace the least valued cart in my shop, which is the planer cart. It’s a great design that works very well but unfortunately I just pile crap on it more often than not.
The design I came up with is very simple and relatively compact. The blower motor sits in the middle on the base of the cart. Four legs hold the plywood panels and four air filters. The top and bottom are just 1/2” plywood. Casters on bottom with the planer on top. Also, and integrated power switch. Very simple. For those who are interested, I have a free SketchUp file available for this cart.
The legs were sized in the design to be regular 2×4 boards. I thought I had some scrap 2x4s on hand but as it turned out I did not. However, I did have some extra 2×10 stock so I cut my material out of them. The first step for almost every project of mine is at my miter saw station. It’s so convenient to have a dedicated miter saw station that can handle large material with ease. It’s also got a ton of storage. I highly recommend making something similar if you can.
After rough cutting to length the boards are ripped at the table saw. I didn’t show it in the video but I actually cleaned these up a little bit at my jointer as well.
Each one of the legs needed to rabbets cut on opposite corners. The dimensions of the rabbets were not symmetrical so this required a different setup for each of the cuts. I chose to use a regular table saw blade to remove the material with two 90 degree passes. In this picture I’m making the final cut on one of the rabbets. Notice that the waste material is on the outside of the blade and not between the blade and the fence. Do not cut rabbets like this with the waste material being removed between the blade and the fence. It will almost always shoot back like a missile when it is cut free.
The first trip to the miter saw was for rough cutting. With all of the leg joinery milled I setup a stop block to cut all of the legs at their final length.
All of the plywood on this project is scrap 1/2” plywood. It’s birch PureBond hardwood plywood. I’ve been using this stuff for over a year now and have not had any problems out of it. And it’s made in the USA and formaldehyde free which are both great.
All of the lower panels are the same size so cutting them is pretty quick.
The blower motor didn’t have anything convenient on it to use to mount it to the cart so I added a couple of scrap pieces of pine. These are secured to the blower housing through the inside with sheet metal screws.
With the mounting situation figured out I transferred the appropriate geometry for the exhaust opening on one of the panels. To cut it out I first drilled four holes on the interior corners and then connected them with a jigsaw. You can get surprisingly straight and smooth jigsaw cuts with a decent blade and a speed square. I’m using an inexpensive 12” plastic speed square here. It’s one of my favorite under-valued tools.
A quick test fit determines I didn’t screw up with my measurements.
For assembly I started with the front and back. To keep everything in place while I drove screws I used a pipe clamp with gentle pressure. I didn’t want the legs to bow up on the sides. Only enough pressure to prevent the panel from sliding as it is secured.
Next, the front and back can be joined the same way with the remaining panels. Side note: Look at those beautiful flags :)
With the frame completed the top and bottom panel dimensions are determined. Again, 1/2” plywood is all that is needed. The top and bottom are the same size.
To secure the top and bottom panel I used one 2” screw per leg.
Where the lower side panels and bottom panel meet I added a strip of really strong duct tape to prevent any air seepage through the joint. This joint is just a butt joint and might open up by a tiny amount over time and I didn’t want unfiltered air to be sucked in. Is there anything that good duct tape can’t fix?
Finally the blower can be installed. I made sure to use appropriate size filters in the design that would allow enough room to pass the blower between the legs.
Four screws were added along both the top and bottom of the exhaust opening to secure the blower to the cart. It’s also just sitting on the base of the cart. These screws prevent it from moving.
The rabbets in the legs provide a surface for the filters to rest against and prevent collapsing in but at this stage there isn’t anything to prevent the top and bottom of the filter from collapsing. So I glued on some scrap plywood for the lower edge of the filter.
And added some scrap pine along the top edge of the filter area.
The electrical is extremely simple. I chose to run power in through a small hole on one of the side panels. A few zip ties on wire on the other side of the plywood prevent the wire from being accidentally pulled back through. From there the power is ran through another set of wires up to a switch mounted on the front of the cart. If the switch is activated power will then run back through the second wire and then power the motor. This is a very simple setup and much greater information can be found on it with a quick Google search.
To make the cabinet mobile I salvaged the casters from the previous cart.
The last step was to add a couple of swivel clips to hold the filters in place. These are just pieces of 5mm hardwood plywood (sold as underlayment plywood locally) secured with a single washer head screw.
And the cart is complete. I really like not only how well this turned out but how easy it was to build.