Filleting a curvilinear corner of 3D Solid Flange

My problematic flanged plate, when being made by hand by the sheetmetal worker, needed to have a 0.08 (or 5/64) in diameter  relief hole drilled between the corners of the flanges to prevent the 0.040 in thick Alclad sheet from developing a crack there after it is bent 90 degrees. The usual trick is to bend the inner face to 3 x thickness of the sheet or more.

Anyway, drawing-wise the corner of the bend may approximate a perfect radius although in real life, there is some necking due to stretching. Once drilled and bent, there is a nice fillet there.

So I was trying to find a way of making such a fillet; well, the forum jury is still out it seems. Don't blame them as it is a an exercise that some CAD workbenches do more easily.

I've thought this through a bit and created one on my model. They take a bit of time to do it seems using my crazy idea.....

Here are the steps:

Fillet for Curvilinear Corner

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1. In 3D Modelling, create a sphere a diameter that skirts the outer arcs of the existing flanges where they meet (only good if the radii are the same). Atomic orbit-like rings appear.

2. Create another sphere at the same centre coordinates but with a radius 1 x material thickness less. More atomic-like rings appear. You show see parallel orbit rings now.

3. Subtract the inner sphere from the outer sphere; nothing much will be seen to be changing except you have a sphere of wall thickness the same as the material thickness of the flange(s).

4. Create a cylinder of the same radius as the fillet radius you need with the centre offset from the origin by a material thickness.

5. Subtract this from the hollow sphere. You will see some strange circles at the back of the sphere due to this subtraction, just ignore them. You will start seeing the curvilinear fillet at this stage, where the flanges meet.

6. Create rectangles to extrude and subtract away the sphere around the curvilinear fillet form. This means you must not select the existing flange entity. Only select the sphere as the entity to subtract from and the extruded rectangle to subtract. This should leave two fillet solids with a right-angled back.  These are still seen by CorelCAD as one solid.

7. In Classic Default, under menu item Solids, click on Solid Editing, then Separate. Separate the two entities.

8. Click on the remote entity and then delete this or copy it for further use at other corners.

9. The remaining entity in the flange corner is now a "curvilinear-fillet" and you may need to tweak its position slightly to ensure it is touching the side of the flanges. Use zoom and 3DAlign as required.

10. Execute the Union function on the curvilinear fillet and the existing flanges/base plate to form a single 3D solid.

If you have a better idea let me know.

My plate attached for experimentation.

I would be interested to know what steps I should take to copy and union the spare fillet to the other 3 corners....

Thank you.