How do I uniformly scale an elliptical shape with straight sides?

Question

I am interested in taking the gray shapes and creating a uniform border around it; an outline with a white interior.

I want to do this by scaling the original shapes and intersecting them eventually. But as you can see with the black shape in the back layer, the curves are not uniform. How do I scale this shape uniformly?

Or if there is a more excellent way, do tell!

Answer 1

Add a stroke to the object and increase to desired thickness. Click Object > Expand, choose stroke. Your stroke will now be an independent object which is a uniform thickness around the object. If you need to make the stroke for each one consistent object, either use "Make Compound Path" or in the Pathfinder window choose all the outline shapes (after you repeat the process for each) and choose merge.

Answer 2

I would add a stroke to the shapes, as a stroke would be consistent Then you can expand your object so that the stroke is a shape as well.

So just draw your shape, put a stroke on it, then go to Object -> Expand. Then fill your expanded shape, now you have two separate shapes, one of which is scaled up properly to your initial shape.

EDIT

You can also scale a stroke with a shape under the transform options. (In case you want to keep the stroke as-is but still maintain its scalability)