re: The Empty Box

Thanks fellow WW's!

I learn new stuff every time.
I always had issues with doing the cove undercuts on mitered frames. I use a 3/4" box core bit in the router table but the exit cuts will expose end grain across the bit and tear/splinter. I'd use a backer but once the cove is partially cut on all sides, the backer will no longer make full contact with the workpiece.

I set the bit height to my target and move the fence back to expose more of the bit, usually about 3-4 small cuts to get to the final profile.

In a "duh!" moment, I finally figured it out.

What I do now is I still use the backer as before (as thick or thicker than the workpiece). This is butted against the outfeed side of the mitered frame and used as a push block plus provides a surface to support the end grain as it gets cut.
What is different is I do all the required passes on only two opposite sides. Push the part through and into the pusher block about 1", flip 180, then repeat. This means the backer is always supporting the wood fibers as it exits the cut. Fence is adjusted and I continue until the final pass is made. At this point I have two sides coved with zero chip out. 

I will then clamp a stop block on the table up against the back side of the fence. I now reset the fence to start the first pass on the two remaining sides. For this, the bit will only encounter long grain as the corners have already been undercut. I make the multiple passes moving the fence back until it hits my stop block.
After this pass (on both sides), the cove meets exactly on the miter joint line. Zero splintering.

Fun thing is as I get older I'll forget and then get to "discover" this method all over again! 🤠