About the only way to tighten up a shaft/bore fit is to get the shaft knurled.
You might be able to do a shade tree version of knurling by using a sharp punch on the shaft to upset some of the metal. The downside of that is you'd need to keep the amount of metal upset the same all around to keep the shaft and the bore concentric.
Or you could use some stud and bearing mount. Link
Depending on how loose your slip fit is, the latter may work just fine.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.