Cutting dados for a built-in bookcase and my jig was off by a hair

I was putting together a big built-in for a client in Phoenix, using my router and a shop-made jig for the shelf dados. The first few went fine, but when I dry-fit the shelves, they were all just a bit too tight. I spent an hour checking my router bit, thinking it was dull. Then I grabbed my digital caliper and measured the jig's guide piece. It was exactly 0.75 inches, but my plywood was measuring 0.73. The jig was perfect, but my material was under spec. I've been blaming my tools for years when the plywood thickness was the real issue. Anyone else run into this with big box store sheet goods?

3 comments

3 Comments

the_kevin2mo ago

Yeah, that "plywood thickness was the real issue" hits home. I always check the actual thickness with calipers before cutting dados now, it saves so much headache.

king.aaron2mo ago

Learned that the hard way on a bookshelf project. I started cutting a test dado on a scrap piece from the same sheet first, then adjust the router bit depth based on that. Saves you from ruining the good panels.

holly_price1mo agoMost Upvoted

Testing on scrap is smart like @king.aaron said, but also check your router's depth stop for any play. A tiny bit of wiggle there can mess up your final cut just as much as wrong plywood thickness. Lock that thing down tight before you start.