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After milling tests, I tried drilling out small hole pattern in the cutting mat (which would make a vacuum table surface for the paper prototyper). Initially I used tiny 0.01" drill bit and drilled a short sequence of holes, only to realize that there would have to be 50x50 grid of 0.01" holes spaced at 0.01", i.e. 2500 holes per square inch. Even without doing the math it was clear that it was going to take forever to drill out 8.5"x11" rectangle on the mini-router, so I switched to 1/32" drill bit, with more realistic 16x16=256 holes per square inch. This would take forever/10 in theory. In reality, one square inch took 10 minutes to drill at 12 IPM which wasn't that bad. Still, at 6 sq.in/hr it was going to take about 20 hours to drill the letter paper size area + 1/2" outside margin.

Here come more mini-router tests - mostly milling soft wood, trying some Delrin. I've run into several issues along the way - they slow down the progress some, but on the other hand they are good learning experiences. 

Dremel runout 

First, the grooves that I initially milled with high speed cutters were about 0.02" wider than the tools. I googled "dremel runout" and found various bits of information, ranging from "Dremel is no good because of runout", to "Runout is much better with chuck as opposed to collet".

Milling plywood was relatively easy. Plastic - a bit more difficult. First, I tried cutting shapes out of black 1/8" thick sheet of what turned out to be polyethylene, according to this plastic id table. I used the same high speed cutter as for plywood - Dremel #194, speed setting 4 and 0.03" depth passes at about 9 IPM. There was a lot of plastic swarf. Then I tried milling a 3/8" thick cutting board made from HDPE. The stuff started melting and forming blobs around the bit, even though I used recommended speed setting (4). After  experiments with speed and feedrate, and online research (good plastic milling info), I switched bits. I wanted to cut gears for RepRap extruder out of HDPE, so I got some small diameter bits on eBay to try.

Finally, here goes: minirouter and first tests with Dremel on plywood. The router had actually been assembled for weeks - it only took me several evenings to assemble it, but few problems came up and I spent time trying to fix them, then fixes/workarounds resulted in new problems and so on. The same flaws and weak spots mentioned in the previous post still remain in the design. Couplings is one of them, and non-alignable leadnut is the other.