How to flatten an uneven workbench top
Shortly after assuming his duties as our new project builder, Chuck Hedlund made it a priority to flatten the benchtops in the WOODŽ magazine shop. Why the rush? According to Chuck, "I find a flat work surface essential to assembling square boxes, flat panels, or four-legged projects hat don't rock. I can't work on a benchtop that's not true." So, we've asked Chuck to show us the best way to level a troublesome benchtop. Here's how he does it.
Note: These procedures work for any solid-wood top that's at least 1" thick. We recommend you flatten your benchtop if it's uneven by more than 1/32:. (You can check for flatness by moving a straightedge across your benchtop.) Do not try these flattening steps on laminated tops made of plywood, particleboard, hardboard or similar materials.
To show you how this technique works, we searched for a bench badly in need of flattening. We found a doozie in the workshop of John Hetherington, one of our photographers. As you can see in photo A, left, this turn-of-the century bench had a warped, irregular surface that was out of flat by more than 1/2". The bench was a great-looking antique, but John wanted to restore its usefulness as a woodworking tool. Although the flattening process that we'll describe here bared new wood on the benchtop, John restored the antique-patina look by rubbing in a combination of stains afterwards.
Start by preparing the bench Before you flatten the bench, you need to make any necessary repairs. As shown in photo B, right, our sample bench had delaminated edge boards that required our attention. You may have to remove the top and retighten, reglue, or reinforce the joints in the base to make it solid and rack-free.
Since you will be routing into the top in the following steps, you need to remove any embedded metal fasteners (such as brads and staples). A metal sensor will aid your search, and save you from dulling or destroying a router bit.
Next, place the bench in the spot in your shop where you will be using it. Check the top for level, and add wood shims to the bottom of the base's legs as necessary (see the drawing below).
With the top as level as possible, attach the shims with adhesive or fasteners. Mark the position of each leg onto the floor so that you can always return the bench to its level location.