I learned a way to use Blend Tool to create shading effect for flat logo design.Here I put same adjustments as the tutorial does, but my shading is not smooth for some reason. I am guessing it's a setting problem but have no idea how to fix it. It would be great if somebody know about how to fix this!
It's as easy as it can get, the number of steps you set is equivalent to the number of cloned shapes between the two (as you can count for yourself in the 10 steps example below, there are 10 clones between the two primary ones) so it's only logical that the more cloned shapes you have between the better it will look. So play around with the number of steps like I did below (go even higher than 1000 if you have to) :
Best of luck !
PS: You should also try and apply this blend mode to a single shape, as I saw in your shadow you applied it to a group of shapes. First unite all the shapes and give it ONLY THE FILL COLOR (no border color) you want your shadow to be and only then duplicate it, change the opacity to the second and apply the blend mode. Looking at your shadow I have a hunch those yellow lines might be caused by a yellow stroke on one of your objects.
When you blend from opaque to transparent, each step is slightly more translucent... so you will see underlying steps.
If you start with a translucent object and attempt to blend to transparent, the issue is worse.
If your blend steps are not a high number, the issue is worse.
Additionally, in your case, it appears as though the "to" or bottom right shape is higher in the stacking order than the center (dumbbell) shape. So, you are stacking translucent objects onto more opaque pieces... making it worse. Appearance may be better if you moved the "to" shape lower in the stacking order.
The best way to address this is to blend opaque objects of varying fill colors rather than using transparency at all. And place the "to" shape below the shape casting the shadow, not above it.
For example, your image could blend from grey to yellow. You can then expand the blend and remove the unwanted pieces -- or just apply a clipping mask on the blend.
It's also much easier to apply a directional gradient in many cases rather than using a blend.