I have been making end plates for my “aluminum frame reel”. I start with a section of rectangular bar, round the corners for lathe clearance, then remove almost all the material with a roughing end mill. Then I make the final cuts (approx. 0.005 inch) on the lathe. Several of these are inner diameters. The right tool for IDs too big to drill is a boring tool.
Here I am working on a rear end plate, holding a round shank boring tool in a home made tool post.
Sherline sells a boring tool made from a 1/4 inch square HSS lathe tool blank, and it is a work of art. Definitely something that I could not produce on a bench grinder. I save mine for special jobs, and use carbide for most work.
On the carbide boring tools that I have, the side cutting edge angle is adequate but the end cutting edge angle is zero. This is OK for boring a through hole, but on a flat bottomed hole the end of the tool will scrape the bottom of the hole at the end of the cut. When boring the shallow recesses of end plates, I turn the tool post at a slight angle to trade side cutting angle for end cutting, allowing me to go to the bottom without scraping.
When boring small diameters, you will need a set of hole gauges. These are by Starrett. The set of four covers IDs from 0.125 to 0.500 inch. A split hemishere is forced outwards by a tapered core, producing an OD that can be measured with a dial caliper or micrometer. I have measured reamed holes with them, and find them to be very accurate and easy to use. Look for them on Ebay.
When I bought my lathe at an on-line auction, many tools were included. These two round shank tools were part of that, and I assume that they are for boring. If anyone recognizes them, I would appreciate knowing more. They do a fantastic job on Delrin.