This post is about making the base and its two routed layers.
Here I’m routing the air distributing plane, with my Dremel fitted with a tile router base and a downcutting bit, which prevents cutting all the way across the MDF in case the bit comes loose and keeps the edges of the routed channels nice and sharp.
I sized my air channels wide enough that I don’t have to be really picky about their exact width, as long as Bernouilli’s law is respected (that’s why the intake path is wider than the following paths). Long story short, to get even pressure on the outlets, you have to have equal pressure along the air paths. Not rocket science, even though it’s part of what actually makes rocket science ;)
After 14 minutes of routing, I have my air distribution layer done and ready to be sanded. I will seal it later, once the base is fully assembled, with liquid varnish, force fed into it, then blown out with pressured air. This will ensure that no moisture gets trapped here and no molds already present in there can develop.
The top layer of the base receives its template. I switch the Dremel to the plunge router attachment, and drill out the 2 mm air outlets to the petri dishes. The central 1mm air outlets are drilled and slightly countersunk at a 45 degree angle to force the airflow towards the output filter intake.
Here you can see the light peeking through one of the central outlets
(I know all this probably sounds chinese to many of you… I’ll make sure to post a video of the actual airflow of the finished box, with smoke to make it visible, once all is said and done; actual visualization sure helps understand what this system is all about!)
The three layers of the base are then glued together, ensuring even pressure on all the surface. The recesses for the petri dishes are routed out after the glue has fully cured and the air distribution system is sealed. Meanwhile, the three glued layers of the base are allowed to cure overnight in the, er, press.
The routed out recesses for the petri dishes, this took some time as I only have a 2 mm aluminum machining bit for my Dremel.
A quick sanding with the same setup helps get everything smooth enough and it’s also a very easy way to remove the template residues.
Next step: build the frame.
-- Thomas - Pondering the inclusion of woodworking into physics and chemistry classes...