Q: Is it Legal?

A: Yes.

This paragraph is from the U.S. Mint website and should clear this up:

Section 331 of Title 18 of the United States code provides criminal penalties for anyone who 'fraudulently alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens any of the coins coined at the Mints of the United States. This statute means that you may be violating the law if you change the appearance of the coin and fraudulently represent it to be other than the altered coin that it is. As a matter of policy, the U.S. Mint does not promote coloring, plating or altering U.S. coinage: however, there are no sanctions against such activity, absent fraudulent intent. (Source U.S. Mint)

The keyword is fraudulent. When you take a 25 cent piece and try to pass it off as a Sacajawea Dollar, that's fraud. When you take a Buffalo Nickel, and scratch out one of its legs and try to sell it as a rare collectible, that's also fraud. But when you take a pre-1965 coin, and turn it into a ring, that's genuine and legal

Q: Can I use my own coin?

A: Yes, If it was made before 1965, and it's a quarter or half dollar, I will gladly turn your coin into a ring for you.

Q: How long does it take to receive my ring?

A: Each ring is custom made when ordered; allow 1 – 4 weeks for arrival. Possibly longer. Your new ring ships one day after final quality control inspection.

Q: Can you use other years than pre 1965?

A: Yes, we make each ring custom for you when ordered. Not all coins are suitable for making coin rings due to their different metal types. For example, we can make a ring out of a standard 1995 quarter, but the copper will turn your finger green. To get around this we can use a silver proof from that year. If you want to do this you will need to supply the coin.