Bill,
I am using 1045 hot rolled 1/2 inch steel bar. It's available on Amazon for $15 for 3 ft. I cut the bar into 12" pieces. I plan to have 8.5 inches extending beyond the handle. I'm not sure aluminum bar has the strength required for this type tool. I purchased the cutters from azcarbide.com. The cutters are available from a number of sources but I didn't want to buy quantity and azcarbide had individual cutters for a reasonable price. I'll post pictures once I complete the tools. I'm building 3 tools round, 2" radius and square. The cost is about $14 for each tool not including the wood for the handles.
Jim