
This Script will create a fillet spline while maintain one point and move the other to make a perfect fillet.



Run script or drag and drop to 3ds max, then go to customize user interface and assign it as keyboard short cut or quad menu under "3D_RnD" Category Its as Easy as selecting 2 vertices and apply the script.
there are three macros :
1- Maintain the Point A and move Point B.
2- Maintain the Point B and move Point A.
3- Extend Both Points to intersect.
By 3D R.n.D