Step 5: The Inner Enclosure
The inner box will not be bearing much weight, and to make the space usage sensible, it is not a massive construction of fire door or kitchen worktop material. Check out the photos for build ideas.
A Note on the Enclosure and Heat
"But won't the motors overheat if they are in an enclosure," I hear you cry. Hold on there, vacuum motors are something of a special case when it comes to cooling. They blast all the air that they suck in through the motor windings (after passing it through a filter to remove the dirt). So long as any subsequent filters (post-motor filters) remain unblocked, this system works perfectly, and means that vacuum motors can be much smaller than they would otherwise be, and wrapped in a convenient insulative plastic case. Incidentally, this is why vacuum motors make very poor motors if we try and re-purpose them for anything other than air moving applications.
For the DS this means that we need to keep a reasonable exit path open for the air being pumped out of the motor, and that we can expect warm to hot air to be travelling this path (step 11 & 14 deals with this). But it also means that we don't have to worry about trying to blow in cool air to pass over the motor, the vacuums themselves do a very good job of that already. Almost all vacuums are fitted with a heat sensitive safety switch, that will cut power if the motor is overheating. If yours has not, it is probably worth adding one, or finding a different vacuum to use.
MDF is typically about 9% urea-formaldehyde resin, it is the stuff that bonds it all together. When we cut it to size we effectively pump out a load of particles of this stuff. Dust is a big MDF hazard (read the first few steps for the lowdown on dust badness). But there is another consideration, particularly if you are sensitive to formaldehyde, and that is the long term 'off gassing' MDF does. Formaldehyde-free MDF does exist, but if we are scavenging our materials one must assume the worst. In this design the 'off gassing' will hopefully be less of a problem as the inner box will be sealed in. In general though, you can control these emissions by finishing the surface with a veneer or a sealing paint, and this is a good practice whenever you make MDF things that will be in living areas.
Lead is great! It can practically be 100% recycled, has fantastical blocking properties, and is comic book style heavy. Lead is not good however, inside the human body! A tiny bit inside, is way more than we want. Luckily it only really gets in there if we are careless. It is best to handle the stuff with thick gloves - you don't want to cut yourself with lead! Wash hands before you eat after handling the stuff. Do not do anything that creates lead dust, unless you have the ultimate dust extractor (presumably you wouldn't be making this in that case!), are wearing a quality ventilator and goggles, and have a way of properly disposing of the dust. I would advise against doing anything that might make lead dust, and really you don't have to because it is so soft - it cuts with tin snips. Don't be tempted to melt it, unless you have the correct safety equipment - the vapour is another way it can get inside you.