Bad quality mesh, Narrow tris as result of Ctrl+t (exporting stl file) I am trying to make a relatively simple 3D-model. resulted quad mesh is very good (fig). however, when I convert the quads to tris I would get this very narrow triangles which I do not want. the only reason that I change the quads to tris is that I need to export the .Stl file, and apparently .stl automatically change the mesh to triangles. 

is there any way to avoid this narrow bad quality triangles?

I've tried to merge them with the adjacent faces, but then they are not triangles anymore, and when I import it as stl file the same narrow triform.
So here is what I did and it worked for me.

After I got the original mesh (left figure on top), I use Remesh modifier with mode set to Smooth. This way I got a very high quality mesh with only quads. When I triangulated the high quality quad mesh none of them became narrow.
However, the size of the .stl file becomes very large. Therefore, I use Decimate modifier to lower the number of faces and keep checking the mesh quality with 3D printing add-on.