Question
My cucumber plants are doing great or at least looks as though they are; however, there are numerous blossoms on the vines but they are not forming cukes,  The same problem exist with my zucunni.

Answer

a very big cucumber   Main Problem is High Nitrogen fertilizer

try using a good organic  vegetable fertilizer with trace minerals,
spray the plant with a liquid seaweed
have you applied compost?
rock dust?

plant needs lots of trace minerals
don't feed it the MG stuff

hope this helps you