Take the 2-minute tour ×  May one prepare coffee ingredients in
a brewer such as this one on Friday and set the timer to brew
the coffee for 8:00 Shabbos morning?  share|improve this
question add comment  2 Answers  In a footnote in this document
it states,  Iggerot Moshe, Orach Chaim 4:60. Rabbi Feinstein
writes that use of timers to automatically regulate machines to
perform work forbidden to Jews on Shabbat is generally
forbidden, with the exception of turning lights on and off. He
believes that use of timers would severely disrupt the Shabbat
atmosphere, since all of one's work could be performed by
machines. Rabbi Feinstein asserts that just as the Sages did not
want, and therefore forbade, our asking non-Jews to perform work
on our behalf on Shabbat for fear that this would disrupt the
Shabbat atmosphere (see Rambam Hilchot Shabbat 6:1), so too the
Sages would not want machines to do work on our behalf during
Shabbat. Rabbi Feinstein appears to be the lone authority to
adopt this approach.  It seems tha