smooth as silk
Lacking impediments or obstacles, unhindered, as in The negotiations went smooth as silk. This simile alludes to the slippery quality of silk. [c. 1900] Also see smooth sailing.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.