If you are making an Ikea Lack enclosure (for example https://blog.prusaprinters.org/cheap-simple-3d-printer-enclosure_7785/ ), you might want to add a third lack table at the bottom to raise it up to a more useful height.

There are a bunch of additional models available for printing extra parts to accomplish this, but sometimes the easiest way is the best. In my mind the easiest way is four wooden dowels and a touch of wood glue.

To drill the holes exactly in the center of the legs and the corresponding face of the table, you can use this drill template. 

The template will allow you to place a pilot hole (3mm or 1/8") dead center in each leg and in the corresponding position in the table. You can then widen the hole to the size of the dowel of your choice.