How to make a hexagon in Eagle?
There is not really a way to do this easily, especially since EAGLE does not know something like shapes.

The simplest approach is to first calculate the coordinates of the edges:

$$x_i=51\cdot\cos\left(\frac{\pi}{180}\cdot\alpha_i\right)$$
$$y_i=51\cdot\sin\left(\frac{\pi}{180}\cdot\alpha_i\right)$$

with \$\alpha_i=0;60;120;...;360\$

and then write this lines to a file with extension *.scr:

CHANGE LAYER 20;
GRID MM;
SET WIRE_BEND 2;
WIRE 0 (51.000 0.000) (25.500 44.167) (-25.500 44.167) (-51.000 0.000) (-25.500 -44.167) (25.500 -44.167) (51.000 0.000);


Layer 20 is the dimension layer. The PCB manufacturer will cut the PCB along the lines drawn there. WIRE_BEND defines how EAGLE connects two points. You want a single, straight line here. And the single 0 of the WIRE-command is the line width.

The file can then be executet by File > run script...

You can also paste this line into the text field just above the layout dawing area.



Note: To move the hexagon, you first have to select all six lines. If you already have some components on your layout, add an offset to the coordinates, so the hexagon is drawn in some distance. You can then select all lines easily and move them to where you want.