Suppose you can set your pair of compasses to length 1. Then
draw a unit circle. Mark a point on the circumference. Step off 6 points with the compasses around the circumference. Take 1 of those points as the center for another circle and repeat. In this way you can mark off straight lines from the center of the original circle of any integer length. These can radiate out at $k.60°$ from each other. Suppose the lengths are $a$ and $b$.
Then we know that the length of the line that would join those two points is
$\sqrt{a^2+b^2-ab}$. It could also be $+ab$ by taking 120°. Anyway, there's a bunch of solutions. Such as $a=3$ and $b=2$.
The simplest construction would use:
Just two circles. Here we use that $a=2$, $b=1$ and 120° gives us $\sqrt{7}$. 