[DonRotolo]

Just a suggestion: When practicing, you may want to consider using styrofoam (the pink or blue stuff sold as Home Depot/Lowe's) or, even better, machining wax (google it, several online suppliers). Both are soft, inexpensive materials that will allow you to machine things without damage if the tool decided to make a cut it can't. Aluminum is less forgiving. Bonus for the wax: Melt the chips into a cake pan and you have a new block.