Techniques for building 'Bed of Nails' testing board

Having the board artwork helps, but if you don't, you can use a sacrificial blank PCB as your template.

Fix the blank PCB the appropriate way up, usually bottom side up, to your bed of nails substrate material. The latter needs to be thick enough to provide the mechanical stability. You can even use two layers for the bed of nails substrate, later separated by a gap, and mechanically joined together by the pogo-pins.

You can use good double sided tape to securely adhere the blank board to the substrates so they do not move relative to one another while you drill.

Then, using a drill press, drill holes wherever you need a test pin, through the PCB and on through the substrates. Use the appropriate sized drill bit for the pogo-pins.

You should also drill alignment holes for larger pins in the bed of nails that will mate with whatever mounting holes you have on the PCB. These pins on the bed of nails should be conical at the tips and longer than the pogo-pins so the board lines up BEFORE it makes contact with the test pins.

I believe pictures are worth a thousand words (?). I documented my DIY Bed-Of-Nails fixture here: https://piconomix.com/creating-a-good-programming-test-jig-is-not-that-hard/

In short, I create a base PCB with spring-loaded Pogo Pins and an upper deck (mezzanine) PCB with holes that the test PCB locates against. HEX Spacers are used to connect the two levels.

WARNING! Beware of tolerances. If your test pad is small (e.g. 1mm diameter) and one of the pogo pins is off-center (e.g. >0.5mm), then it will not make contact, or worse be intermittent and that will ruin your day.

A more DIY-friendly option that I've recently discovered is a "plug of nails" interface (example). One end of the cable has pogo pins, alignment pins, and tabs to hold the connector in place. The other end of the cable has a standard header that you can connect to your test fixture. The datasheet for that particular part shows the pattern of holes and contacts that you'd need to add to your circuit board.

This sort of solution would require you to route test signals to a central location instead of being able to place them anywhere on the board, but would eliminate the difficulty/hassle associated with the physical construction of a traditional bed-of-nails test rig. For boards with a relatively small number of test points, I've found this to be worth the trade-off.