What kind of drill bit do I need to drill through roughly 1/4" of "356 T6 aluminum"?

You need two cobalt steel drill bits, a punch, and some cutting oil. Locate the hole and pin punch the spot. Use a 3/16" cobalt steel bit and make a pilot. Use lots of oil so the aluminum doesn't discolor with the heat. Then drill the 3/8" hole to final spec. Continue to use the cutting oil while drilling the second hole.

Good luck, man.

Usually it is recommended that a chip breaking drill and pilot holes are used on any T6 alloy aluminum, but since you only need two holes, and the thickness is only 1/4", that isn't even an issue for you. Any 3/8" steel "jobber" high speed bit will work just fine.

pilot holes are always good for holes larger than 1/4". but if accuracy isn't critical a 3/8" hole in aluminum should not be a problem. it's easier to keep a small bit from "walking around" while getting the bit started. using a center punch first to make a dent in the center of where you'd like to drill is the most help. good luck!

One of your problems with that is that you fail to take into account the cost of getting that oil out of the ground to the price of oil. They take the cheapest oil to get out first. That cheap oil was in the Middle East. That's also why we declined in production since 1970. We don't have all that much oil. Even if we did, we don't own it, we lease the areas to the oil companies and they charge us the going rate. One day any way you look at it we will be out of it. We need to seriously look into developing new engines that won't need gas to function. Something renewable, and affordable. I'm tired of looking into alternatives that you have to be rich to afford, like solar panels for the home. There is just no payback there for longer than I'll be alive.

use a step drill bit

center punch any standard h.s drill bit