[Kevin Sevcik]

ok... I think dez250's post was slightly confused, since liquid nitrogen shrinks metal. at any rate, that's not an option for you unless you get a new gear or shaft because your shaft already fits inside the gear. But I understand that thermal interference fits are a relatively standard thing in practice. Heat a hole up, cool down a shaft, stick'em together real quick and you're done. I'm not sure of the load carrying capabilities, though. probably depends a lot on the interference and roughness of the shaft and holes and such.