Tapping with left or right thumb does not utilize tools

When I want to chop trees or dig dirt, etc. I can only do so by tapping directly on the object. When I align myself with an object and tap with my left or right thumb, the tool is swung but nothing happens.

[mastery51]

So What i think you are doing is (correct me if I'm wrong) standing next to a tree and or block. But you are not tapping on the object directly hoping the sprite animation will dig it up. If that is the case then you have to tap on the object directly only to dig up resource.
Also keep in mind that each tool has it's own digging range. So if your to far from an object with, let's say a wood pickaxe, nothing will happen untill your close enough to object.
I hope I answered your question?

So I can only dig or chop by tapping on the object directly? If so, why does he do dig or chop motion when I just tap the left or right side of the screen with my thumbs? Thanks!

[mastery51]

Because the game thinks you are wanting to break the block or tree on the left or right side of the screen that you are directly tapping on. You don't need to stand right next to the tree or block to dig it. You can tap any item anywhere on screen to break the item, provided by a tool that has a far enough range to do so. For example in this picture I have an Antanium pickaxe and I can dig-up as far as the block or item that has the red x on it with out moving any closer.

Oh ok, that makes sense, thanks!

yeah you need to be in range and tap on what you want to mine or place