I have a 1/2" aluminum disc 2 5/8" in diameter. I have drilled a 3/4" center hole. Making a piece for an old wood jointer. I would like to face the disc down to 7/16" but I don't know how to best hold it in the lathe on my 7" x 10". I used a 3/8" bolt to turn the diameter down but that ruined the bolt and I had to but it off. Any ideas?