How to change the inherited F-curve independently from the original one ?

what I did:

I created a hammer, inserted two keyframes to rotate it a bit, set the curve to linear and extrapolated it linearly. Than I duplicated the hammer, the result was two hammers that spins synchronous.

What I want to achieve:

I would like the second hammer to spin with only half the speed or I would like to create a few hammers and each one spins some degrees ahead of the other. But I only have one curve in the graph editor for both.

You could also try to use F-Curve-Modifiers. To do so:

1. Go to frame 0 and add a keyframe on the rotation Axes you want
2. In the Graph Editor bring up that sidebar by pressing N. Add a Modifier > Generator. This will give you the polinominal tools to create a Graph as in y=mx+b as you might remember from school.

3. This value controls the ascent of the curve. By default it's 1, so we have y=0+1x, so y=x meaning that for each 1 frame (one unit on the x axis), the curve ascends 1 unit on the y axis as well (it actually goes up to 57,296 because 1 rad= 57,296°).

So if you want to have a second object that rotates half of that speed, you just enter half of the value you entered at (3), 0.5 in my example.

Use the NLA editor

The Pushdown (double down arrow [insert icon] in the action or NLA editor moves the action to the NLA.

Changing the speed of an animation is described in controlling speed of an action by driver or scripting

Move the action strip to offset the start time.