Minimum thickness of panel for frame and panel door?

[srp]

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I ddin't see this until after I had composed and posted my last reply. I believe that reply will serve as a reply to the point you raise above. My main reason for responding is that I have NEVER made a cabinet out of chipboard.

That's fine. Just use solid timber then. As I pointed out, a rubbed joint in 6mm will be perfectly satisfactory as long as the panel is floating within the frame, as there are no stresses acting on it.