No good reason to cut up good shafts if you can get alu stock from a supply house.
McMaster Carr carries alu tube in most sizes. PN:89965K45 should fit Cx shafts and is onlt $12 for a 6' length. They even have steel tube if you want a heavier footing.
If you have a local supply shop they can most likely order about any ID/OD tube you need if you ask them.
Edit: Forgot to mention, 3R already has machined footings that will fit most any shaft. No need to cut up their expensive aluminum.