Two Original 3-Way Corner Joints.

I've seen several versions of 3-way corner joints done in wood by assorted YouTube and woodworker web sites. Other than a double miter cut on all three pieces most require unique cuts on some or all three of the connecting boards. 

I've already come up with one version that can be CNC cut the same on all three pieces, but it required a center block that each piece connected into to complete the assembly. That 4th part cube was more challenging to make than the corner joint cuts were. 

https://4dfurniture.blogspot.com/2016/11/original-cnc-cut-3-way-interlocking.html

This post is my pursuit for unique looking joints that can be cut using a CNC. All three joining pieces must have the same shape done by the same toolpath cuts. 

One potential for a good looking solution is that the details in it may inspire similar details in the rest of the project these corners are used for. A new style perhaps.

The outer corner presents the most significant challenge.  

Pinwheeling around the outer corner each joint line will end up at the inner corners of the connection. This line doesn't need to be direct from outer to inner corner.  A curving line or bumpy line or zig-zag line should also work so long as each side of the line can be cut with the cylindrical or conical bits used by the CNC.  

One example I've made has concave/convex curves on each face as shown here: 

The only flaw in this design is that it leaves a small hidden 3-sided void in the center core.  The curves might encourage some curves in the design the joint was used for.  Perhaps a slight curved taper from the inside corner down to the foot.  One face of the leg might have a convex taper while the other face might have a concave taper. There could even be a shallow arc or bow on the underside of the top rails from leg to leg.  If the table is rectangular then the long sides might have a slight convex bow while the short sides could a slight concave arc. 

Stepped 3-way Miter

Another example is this stepped miter corner joint.  Each piece can be cut with a CNC using the same toolpaths,   Only a little bit of chisel work is needed to take care of two rounded over edges that couldn't be reached by a spinning router bit without messing up another detail of the joint. See the image above.  Each piece ends up with 2 and 2/3 of the 8 cubed volume, leaving the entire volume perfectly filled when assembled.  Cut out and cleaned up, then glued together it is easy to clamp. The flat steps on each piece keep the parts from sliding against each other when clamped down. The stepped joint might encourage a stepped detail to the furniture piece they could be used for. 

Stepped 3-way Miter in Pine

This sample shows a little tear out left by the pocket toolpaths.  It was easy to clamp up. I like the contrast between side grain and face grain on each side, helping the joint line stand out.  

I've got a few more sketched ideas for a corner joint.  I'll need to find some more scraps to see if they'll work and show how well they glue up and actually look.  A good bit of mental exercise this pursuit has been.  Making the toolpaths for the stepped miter corner was the most challenging part. Trying to visualize how the curved version would work before actually making it was a bit beyond me.  I didn't foresee the hidden void left in the core. This proves how valuable it is to make sample prototypes. 

Comments and Questions are encouraged and welcomed.     

4D