Vacuum table

This is a vacuum table to hold photographic prints flat while copying. It does not work as well as I hoped.

I originally designed this with 1mm holes in a flat surface, unfortunately, my printer could not print the holes that small, and I had to manually drill out the holes. With 1mm holes this did not work at all.
I designed in a valve to allow extra air to the vacuum to prevent the motor overheating, but it needs to be fully closed. I under estimated how much air would get through the array of holes.
My goal was to have the holes small enough that the vacuum remained rather high, but the small holes did not allow enough air through to keep air seeping in under the print and allowing it to curl up.
I created an adapter that allowed me to use my shop vac for more airflow. This did not help
I tried counter sinking the holes with a 6mm drill (I wanted a very shallow countersink angle) to allow the vacuum to work on a larger surface area. This also did not work.
I tried opening up