Measure the area where the desk will be placed. Determine the size and dimensions of your desk. Draw a simple sketch on graph paper.
Cut the butcher block with a circular saw according to your dimensions.
Sand the edges of the butcher block with fine grit sandpaper until they are smooth and soft to the touch. Wipe off sanding dust with a tack cloth.
Measure and cut wood trim to cover the edges of the block. Attach the trim with construction adhesive. Hammer finish nails every eight inches to firmly secure the trim. Patch the nail holes with wood putty. This step is optional. Some people like the square edge of a butcher block and prefer to leave it as-is.
Spread construction adhesive on the top of the filing cabinets. Place it on the top of the cabinets in a zig-zag pattern. Make sure the adhesive goes all the way to the edge of the filing cabinets.
Set the butcher block on top of the filing cabinet. Press it firmly into the adhesive. Set a heavy object on each end to hold the block in place. Let the adhesive dry overnight.