Spinoff: the American Civil War never happened. How long until slavery ended?

American chattel Slavery was on its way out already due to the rise of industrialization and machines, much like the manual and menial labor of today is being replaced by robotics (which you could argue to simply be another form of slavery, but that's another thread for another night.)

Had the violence not broken out and the myriad reasons for the civil war not ignited the powder keg, how long before slavery was done away with voluntarily?

The cost of feeding, housing, caring for and tending to humans is extreme, and one has to think that once a mechanical alternative that allowed farmers to do the work of hundreds with only a few, voluntary manumission would become more commonplace.

I think by the turn of the century (or sooner) you'd have transitioned to a U.S. Where slavery wouldn't exist in the form we know it, if at all.

Especially with the flood of Immigrants who were cheaper and much more expendable than slaves, you'd see a dramatic shift towards hiring workers, or perhaps freeing all slaves and allowing those who wished to remain on voluntarily resigning themselves to a period of indentured servitude.

What do you think? How long would it have taken and would the situation have been better or worse? What would the driving factors be?