It took some time/ frustration to get the splines cut to the right thickness. I cut the spline space with my thickest saw kerf. Used sandpaper to get the thickness of material I needed. I thought about making a plane carriage for the thickness but I just used sandpaper. ***It went better when I stopped working small and allowed myself to waste some material by cutting wider splines. The splines were then easier to handle and sand.
A 16oz. steel hammer helped “shock” the spline into place. I broke a few, but I just let it dry and cut the slot again.
It is amazing how the splines strengthen the miter.