How to draw NACA 6-Series Airfoils?
From this reference:

$$c_f=K_1\cdot \frac {t}{c} + K_2(\frac {t}{c})^2 +  K_3(\frac {t}{c})^3 + K_4(\frac {t}{c})^4$$

For the 64A series: 


$K_1$ = 8.2125018    
$K_2$ = 0.7685596    
$K_3$ = 1.4922345    
$K_4$ = 3.6130133


$c_f$ is the particular scale factor for this profile. And then the reference continues with this head spinning further explanation:


  Now, for a specified family and thickness, the thickness distribution may be determined without iteration. From the thickness, the scale factor is computed from the polynomial function shown above. Then, the scale factor is used to multiply the basic values of the psi and epsilon functions for this airfoil family. These scaled psi and epsilon functions are used in mapping the z-plane to the z'-plane shown in Figure 1. The Joukowski function zeta = z' + 1/z' then maps the z'-plane into the zeta-plane and these results are normalized so that the leading edge is at x=0 and the trailing edge is at x=1.


Hope this helps, my head hurts after reading that.