Using a taper will work but makes it very tough to get the longitudinal
position correct.

dave wrote:
idea:

cut slight taper on part to be inserted (less than a morse taper, like a
degree, or maybe even half a degree), with matching taper in the axle
end. freeze spindles, heat outer tube, slam together "pronto-like" (wood
block, vice, huge hammer). bonded forever, no welding, no add'l fasteners.

reamers -might- be available in sizes correct for the outer tube, to
simplify things...