1/2" round rod

How tight of fit? How much length of the rod needs to go into the bearing? Aluminum is soft. A regular 1/2" bit and sand/polish down the rod a touch with progressively 220, 350, 600, 1000 grit sand paper. The job or use of your project may determine the required/ degree of sanding/polishing that's appropriate.

Sonny

You can pick these up at almost any hardware store.

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You didn't say what the bearing is made of. Only that the rod is al. This method works with metals like brass or bronze. I don't recommend aluminum-to-aluminum contact for bearings/shafts.

Drill with a regular 1/2" twist bit. Make sure it is sharp. Then ream with an oversize reamer, .505".

Use a drill press. Clamp everything down good (a cross-slide vise works well). Don't move the clamps or the quill between drilling and reaming.

You can get the drill bit at any big box store, but you probably need a fairly well stocked machine tool outlet for the reamer. I've seen them as low as $17 for the size you need.

Frank