You have described the Alberti cipher, outlined in Leon Battista Alberti's 1467 treatise on encipherment, De Cifris (Alberti, Leon Battista, A Treatise on Ciphers, trans. A. Zaccagnini. Foreword by David Kahn, Galimberti, Torino 1997). The original Italian version, with illustrations, is De componendis cifris.
Alberti's work marked an important innovation in Western cryptography, the polyalphabetic system. Whitfield Diffie often talks about this, by the way.
Whitfield Diffie points out that Alberti's notable advance for cryptography clarified the distinction between a cryptographic key and a cryptographic system. Before the Renaissance, this distinction was difficult to make because the systems were very simple. For example, in using a codebook, all of the expense is put into the codebook, the secret piece, not into the system of looking up plaintext and writing ciphertext. Alberti's cipher resisted cryptanalysis by advancing from the current monoalphabetic systems to a polyalphabetic system. Importantly, it shifted the expense to the public piece, the system, making the secret part cheap.
This story is important in the history of cryptography, but we cannot use Alberti's cipher to secure communications today. It would be trivial to very rapidly break such messages with a modern computer.
In short, classical cryptography is useless against today's computers (excluding codebooks and one-time pads, two methods very rarely used, it seems).
For more detail on Alberti's fascinating work, see:
Williams, K., March, L., Wassell, S. R. (Eds.). (2010). The Mathematical Works of Leon Battista Alberti. Springer Basel AG . pp. 189-200.