[Shop-talk] coupling two shafts

[Randall]

> the output shaft of the gear drive is 3/4" and keyed
> the other shaft is smooth and 1-9/16" diameter. 

Flipping through the MMC web site, I see several "mix n match" shaft
couplings that seem like they would meet your needs.

For example, two 6407K43 plus a 6407K53 might do, for about $60 plus
shipping and tax.
http://www.mcmaster.com/#shaft-couplings/=ai8f3y

-- Randall