Here is a wizard to make the code to warm up a spindle.  Place this mcs file in the Wizards folder for M4 and use it from the Wizards pull-down menu.

cool

Slightly corrected version. With the original, I always was starting at 1000rpm. Not quite what we're looking for when our router/spindle's slowest speed is 3000. So I corrected the While loop to start at the requested startRPM and then increment by  the step increment over the time specified. This version goes one increment over the requested max rpm

Is it important to warm up the spindle?

If, yes for how long time? and do you just let it run at a certain sped or....?

Thanks