Circles larger than the cutting area (the easy way)

Building a rotating bookshelf for my youngest and thought of an easy way to cut the circular shelves.

I have 6mm holes in my spoilboard, so I simply cut a 6mm hole in the middle of my square stock. Then I connected both with a metal pin as a pivot point. Then I moved the router in position above the stock and while I moved down the bit very slowly I started rotating the stock by hand. For the finishing pass I moved the bit slightly closer to the pin and kept turning the workpiece.


How it will look when done:


That’s pretty cool. I’ve seen that same technique using a table saw.

And a band saw and a router table, but for reason, I’ve never thought about using the cnc like that. Thanks for sharing.

Yeah, I kinda think of it as an inverse router table, which can be beneficial from a dust extraction perspective as well.
I guess you could use a flush trim bit with a bearing the same way.

Now what the CNC version could do for you is a wavy pattern on the circle, though you might want to rig something up to rotate the piece at a steady speed…

I’d not be confident in my ability to do this. I’d probably work with registration holes and machine 4 quadrants individually, each time with proper work holding.

I’m actually planning to do this for the dowel hole pattern I want to machine into these circular shelves. Stay tuned!

Started adding bolt and dowel holes to these circular shelves and thought of a (somewhat) easy way to do this with the CNC even though the shelves are larger than the cutting area. I basically rotate the workpiece using the CNC.

Given that I need to machine four identical quadrants, I machine one, then for the last feature I just run the bit straight down into the workpiece and turn off the router and remove the clamps. I have added a pause command to the GCODE at that point. Then it does a 90 degree arc move with my pivot point at the center, rotating the work piece as it moves. Then I fix the clamps, turn on the router and resume the gcode, letting it mill the last feature. I repeat this 4 times.

Video showing the MPCNC rotating the workpiece.


Sets piece up, places dowel, moves the head the legnth of the radius. G92 x0 y0 z20. G1 z0 f1. 20 minutes and 20 spins later, and you’re through 3/4 stock. Obviously I’m used to 60+ inch circles, and hardwood stock.