I also use this setup.I mounted a thin project box to the table with a laser pointer, a mirror at 45 deg and a pinhole inside to illuminate the bottom of the PCB. The pin hole is made by mounting a brass shim and drilling the hole with the smallest bit that you have. A degree of fiddling is necessary to get the laser beam directly centered on the pinhole. But once it is adjusted, the beam is strong enough to illuminate the hole to be drilled from below. There is also a bit of diffusion through the FR4, but the center of the spot of light is exactly aligned with the bit. the top of the project box serves as the table which is OK for small PCBs.
The drawback is that once it is calibrated you can't remove the rotary tool or rotate the arm. This arrangement largely eliminates the depth perception problem; where the spot of light is, is where the drill bit will penetrate the PCB.
Baxter
--- In Homebrew_PCBs@yahoogroups.com, "tda7000" <Tda7000@...> wrote:
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> I use a Proxxon FBS rotary tool in a Proxxon 140/S stand Lhttp://www.proxxon.com/eng/html/28606.php)
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