The "Urim & Thummim" were perhaps Joseph's own eyes, which in a mystical state of consciousness could "see" the visionary "plates." He lost these "gifts" for a time.
If Joseph made the plates he had in his possession, then didn't he lie in saying otherwise? Maybe there is more to it, which ties into the mystical nature of his visions.
I suggest that Joseph Smith's earliest direct encounters with God happened in mystical experience, or what is also known as altered states of consciousness.
And being admonished by these books to return into myself, I entered into my inward soul, guided by thee... And I entered, and with the eye of my soul—such as it was—saw above the same eye of my soul and above my mind the Immutable Light.