I needed to make an enclosure for my cnc micro mill to contain dust and chips, so I grabbed some 3030 extrusion, and used some high quality double sided tape to mount 0.060" (~1.5mm) clear polycarbonate I had laying around.  

There are two version, one that accommodates the polycarbonate sheet, and one for just the extrusion.  They have two holes for #8 wood screws (I mounted mine to a baltic plywood top on my micro mills workbench).  There are screw holes if you want to screw into the 3030 extrusion (though you will need to drill and tap the aluminium) that I am not using since I want to easily be able to move the enclosure.  

The frame becomes surprisingly stable, and holds very well, while still being easy enough to lift off to access the back of the machines. This lifts the 3030 off the bench enough that I can pass wires under.  I will design and print snap in fillers to prevent dust from blowing under panels.

I used these corners for the enclosure: