This was cut from black .157 coroplast from Home Depot. The approximate 425 holes were cut with Inventables Solid Carbide Single Flute Upcut End Mill #30238-02. I tried a typical 1/8" 2 flute downcut and upcut bit but neither cut the holes as smooth.
Use a waste board under the plastic. It tends to flex when cut so you need to cut deeper to make sure it is clean. I used normal clamps to hold the plastic in place but don’t over tighten and crush it.
If the holes are cut just the right size the lights will “pop” in and stay in place. The holes in my template were drawn at .310" and were to be cut with the 1/8" bit. But cutting a few sample holes showed them to be too small. Rather than adjust all the holes I just played with the bit size. Making the bit smaller produces a larger hole and with my lights I found .110 worked well.
But have you lights on hand BEFORE you cut and adjust accordingly. Also, the LED lights we were finding all had a small tab to hold the “bulb” in the socket. I did not account for this when I made the template and did not want to rework it. As a result, we used old style incandescent lights (no tabs). When installing all the lights I realized had I went back and cut out for the tabs it would have been a real challenge to get each light twisted to accommodate the tab. I would prefer LEDs but only if I could find them without the tabs.
Sign was designed so the frequency could be changed at a later date if needed by just re stringing the lights.