  We report the all-optical production of Bose Einstein condensates (BEC) of
$^{39}$K atoms. We directly load $3 \times 10^{7}$ atoms in a large volume
optical dipole trap from gray molasses on the D1 transition. We then apply a
small magnetic quadrupole field to polarize the sample before transferring the
atoms in a tightly confining optical trap. Evaporative cooling is finally
performed close to a Feshbach resonance to enhance the scattering length. Our
setup allows to cross the BEC threshold with $3 \times 10^5$ atoms every 7s. As
an illustration of the interest of the tunability of the interactions we study
the expansion of Bose-Einstein condensates in the 1D to 3D crossover.
