The manual to assembling it is attached to the post. 
I have 1 and 3 year old beta-testers so the current design is reasonably battle-tested;

Although it can still be improved. 

While printing the head:

For best effect for bubbles try to increase the print temperature above the recommended, and set seams to random. The stringing actually increases the surface on which the soapy water can grab onto and thus helps the bubbles. 
I also recommend a brim.

UPDATE: updated the head based on an additional detail I noticed on commercial bubble blower!