Fume-hood DIY
In a maker’s workshop it is not uncommon to conduct processes and operations that might have less-than-pleasant behaviour in terms of emitted gases and dangers of flying shards. If one is dealing with chemical coatings or metal refinement, or even just cleaning parts in nasty solvents, then it is beneficial to have a place where you can do it while minimizing chances of your contact with the hazardous materials. That’s what fume-hoods are for. A fume hood is just a cabinet with a vent duct attached so that air is sucked from the room into the cabinet, preventing the contaminants from spreading into the room. The cabinet must also have a transparent “door” that is usually implemented as a sliding window. There are, of course, nice fume hoods on the market, but they are usually designed for industrial-grade chemistry labs and one of those will set you back anywhere from 2k to 20k easily. On other hand, for a typical DIYer something much simpler (like a grandma’s wardrobe) may be just enough for the purpose. I decided to go somewhere in-between. It is not that expensive to order custom-cut chipboard panels from your local furniture factory, given that you get a direct contact with the manufacturing department. I had one, so the only thing left was to make drawings and a specification sheet for the order. Not to delay the reader any further, here is the design:
The working volume is of prismatic shape. This allows the window to be slanted, which reduces unwanted reflections along the line-of-sight and makes room for the operator to tilt head a bit down during the operations. On the sides of the working volume aluminum rails are mounted to allow the window’s sliding action. On top there is a stretcher to add rigidity to the side walls and “ears” as mounting surfaces for cams of the window counterweight system.
Under the working volume the storage zone is located. It is divided into three functional zones: drawers, container storage and vertical storage. Drawers are used for small quick access items like adapters, stoppers, small beakers, etc. Container storage is sized specifically for plastic containers I’m using (it is not Ikea, so check that your preferred box size fits in case you’re going to replicate this). The vertical storage is intended for high cylinders and long pipettes.
As I got the panels from the factory, the first thing was to call my friends to get some help with the assembling, as there was quite a bit of it. And then the work started:
I always hated the “traditional” cheap drawers with a thin 3mm fiberboard bottoms. So here I used 10mm chipboard and reinforced the joints with aluminum profiles. The last decision turned out to be a complete overkill, so I would not recommend it.
Then the base and the hood are assembled separately. Whenever possible I preferred to use confirmat screws because it is easy to drill all the holes in-place. For less accessible joints (like between the base and the hood) I had to resort to dowels and minifixes. For some of the drilling operations a drill guide came handy and I have mentioned one at the end of the 3-part series about spot welding machine.
The window is assembled from aluminum extrusions and Polycarbonate sheet. PC was chosen because of its high toughness which makes it a great safety shield. On the top of the hood an opening was carved out and a duct adapter was attached.
The two pieces are easy enough to assemble at the place of installation so there is no need to move the whole thing through the doors. The sliding window is kept in balance by a pair of counterweights located at the hood’s back and attached to the window with cables that run around the cams on top. To eliminate dangling of the weights, they are supported by drawer slides placed vertically on the back wall. If the counterweights are precisely adjusted, the window is in neutral equilibrium which means that it may be moved to any position and it stays there without any locking.
A not-so-sophisticated solution is used to control the air valve on the duct:
A lever is attached to the valve’s axis rigidly, while a mop handle has rotational freedom around a screw that sticks out from the lever. Position at which the lever is fixed on the valve’s axis is important: the screw must reach the highest point and the lever approaches the vertical direction when the valve is half-open. When adjusted this way, the system becomes bistable: in both fully opened and fully closed positions, the handle’s weight tends to lock the valve in that state.
And finally the bottom of the working space is paved with ceramic tiles glued with epoxy. A water distribution system is also installed on the back wall.
It was hard to get a proper drainage pipe connection to the installation place and also to install a sink at the bottom, so I decided to use just a regular water 32mm PP pipe for water return from condensers and coolers that will be attached to it with same kind of fittings as used in the water supply. Whence the two rows of outlets. As it takes a little bit of pressure to push the water on its return path through that thin (and long) pipe, the unused drainage outlets have to be kept closed with the valves.
And here is a typical setup that makes use of the fume-hood with its water supply connections:
For finer control of the water flow a needle valve and a rotameter may be attached to the inlet:
This concludes the build of the fume-hood. In case you got interested what is it there under the flask on the last photo, that’s a magnetic stirrer from my previous post. And if you want to read a couple of things about general workshop improvement, there are some ideas.
