A while back I did a thread on this in the Lounge ( https://community.carbide3d.com/t/using-abusing-multi-layer-v-carves-for-joinery/19711 ) — since then, the V carving features in Carbide Create have gotten much more flexible, so it’s a bit more straight-forward to use (abuse?) them for this, esp. if one uses two 90 degree V endmills, one large enough to cut all the way through the board leaving a 45 degree angle at the end, the other suitably smaller (exactly how much smaller it must be will be worked out in the course of drawing this up and modeling it).

It’s being written up formally at:

https://willadams.gitbook.io/design-into-3d/blind-miter-and-hidden-spline

and I’ll be writing and posting each bit here, then tidying it up and re-posting it there.