Getting all four feet of a chair or table in the same plane can be a challenge. What makes the task more difficult is that it can be difficult to figure out when you are done with the job of leveling the feet. After all, your shop floor, your workbench or your table saw are unlikely to be truly flat.
What do you do? (Besides buying shag carpet for every room of your customer’s home.)
Here’s how I deal with it. I have a section of plywood that I regularly confirm is flat with the help of a straightedge. After I level the legs of a chair or small table, I flip the project upside down on my workbench and then place the plywood on top of the upturned feet.
If the plywood doesn’t rock on the feet, then I’m done.
But if the plywood does teeter on two of the feet I can easily see the culprits. I remove the plywood and shave down the high feet with a block plane. Then I test the feet again and repeat until all four feet touch the plywood.
Then I can say with confidence: Your chair is rocking because your floor is uneven. Move the chair to another spot and try again.
— Christopher Schwarz