PCB milling: how to verifiy the accuracy of routed traces

Inspecting an Eagle PCB milled board

Here is how I verify that my pcbgcode settings are good, and more precisely, how accurate the "etched" traces are, in relation to the depth of cut. The latter is not easy to set when using V-shaped mill bits, since the deeper, the wider the traces. The one below, between two pads is only 0.01 inch, i.e. 10 mils, and it was properly milled.

The trick was to overlay the live image from an USB microscope over the Eagle board design, scaling the windows appropriately. I applied 50% transparency to the webcam window (I am using ''cheese'' here), which is trivial with Kubuntu / linux. The microscope is an Andonstar, a great & cheap tool, for which I wrote a micro-review here.

By the way, I will no more use these "titanium" coated V mill bits, as they produce rough edges compared to the cheaper ones I bought earlier on ebay. This board is just ugly. Well, the PCB copper clad is also a super cheap one (I bought a lot "50Pcs 70 x 100 x 1.5mm FR-4 Single Side Copper Clad PCB Laminate Board" for $37 on ebay: I could not expect much but they are NOT FR4 but old style bakelite, not fiber glass! Much more fragile, not really worth).

Also my holes are slightly off-center, but not bad enough to be fatal here. Cheap 0.8 mm drills?

Review: microscope for electronics (three Andonstar USB microscopes)

Here: fixing a board (0805 SMT resistors near a µSD socket, 0.6 mm wires).
A microscope is a much needed tool to inspect electronics, or to work at small scales.

(shot on my $160 workhorse, a very good Andonstar ADSM302)

This post shows the microscopes I have been using so far, sorted in historical order. This is also sorted by price, not surprisingly: with time my gear tend to get more expensive...
I am using microscopes all the time to inspect PCBs, read SMT component values, work at small scales, or whenever my (ageing) eyes are tired... And it feels like being in another world when you end up raising your eye back to the reality after a few hours :)