15 Jun You May Not Need a Chisel for Those Inside Corners
Anyone who runs a CNC router is familiar with the ‘dogbone’ treatment for inside corners. That’s where the machine compensates for using a round router bit in square corners by making a Mickey Mouse ear on each corner (the drawing in the middle of the photo).
While using traditional tools to make a half-lapped poster frame for a customer the other day, I had a small revelation. As usual, I extended the pencil lines to guide my chisel cuts when cleaning out the corners. Then I reached for a sharp chisel. Those corners were round because I had used a bearing-guided rabbeting bit in a portable router to create the rabbet for the glass. That’s a process we’re all familiar with.
There was a Forstner bit lying on the bench, and suddenly the penny dropped. Instead of scoring and chiseling each corner and risking splitting the hickory frame with each hammer blow, I could use a power tool!
The first step was to drill a small pilot hole at each corner where the two lines crossed (top right in photo). That would catch the center tip of the Forstner bit and prevent it wandering. Then I chucked the larger bit in the drill and made the ‘ears’ freehand. I was a bit concerned that the bit might dig too deeply, but it was really easy to stop and monitor progress. The whole operation (all four corners) took maybe a minute, which is a lot less time than chiseling. And the result is a very clean pocket in the back of the poster frame, where nobody will ever see it.
While picture and photo frames probably won’t need any dressing up, one could ‘fix’ the Forstner bit cavity on the backs of cabinet doors by installing custom cut wooden plugs. These plugs could be the same species or a contrasting one, for decorative effect. Large plugs would be an ideal solution for glazed furniture doors, where the back is revealed when the door is opened. Suppliers such as Lee Valley sell larger diameter plug cutters, both individually and in sets. One could cut the plug, remove the slice of the pie for the inside corner on the frame (using a back saw or even a scroll saw), and then glue the rest of the plug into the hole.
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