CNC cut Radiused Corners for Furniture Projects

I would occasionally have students design a cabinet box with radiused corners.  Before we had CNCs to use we might run the corner board across the table saw blade at an angle to cut the inside cove. Optionally we might use a cove bit or large ball end bit on the router table. Follow with a few angled table saw slices to remove much of the outside surface.  Then plane/scrape/sand away to smooth out the outer surface of the corner. 

Using a 3-axis CNC and Aspire software, and the job set up as a 2-sided job, both the inside and outside faces of the corner curve can be cut. 

The goal is to remove the red shaded areas from the rectangular starting block. 

Top and Bottom cut Areas

As the whole top area of both sides is being cut, an extra inch was added on both ends for a place to clamp it down.  The moulding toolpath in Aspire software using vector drawings of the section views makes easy work of removing the waste areas to leave a perfect curved corner. The 1" ends can then be trimmed off. 

Inside Surface

Outside Surface

Care must be taken to align the board when flipping to do the second side. The material used and grain direction of the board should also be considered when cutting the adjoining flat side of the cabinet box. Plywood could be used with corners with grain running as shown in the renders above.  The grain direction of hardwood sides must match the grain direction of the corners. Front to back for the examples shown, Use Biscuits or Dominos to join the curved corners to the flat sides. Cutting a slot for a spline between adjacent parts could also work. 

This same strategy can be used to make corner sections that aren't 90 degree. I had a student from another class request how to make radiused corners to attach angled wings for a chair seat.   With the potential load on the wings of the chair seat being fairly great he eventually attached them with metal brackets.  Wood corners might split in such cases. 

A hexagon box with radiused corner would be a great application for CNC cut corners. Just draw up the inside and outside vectors of a 120 degree corner section. A few other drafting tricks might be needed.  :)

4D

Comments or Questions welcomed and appreciated!