"Thick" vectors from thick lines in B&W drawing

hello everyone, I am converting images from jpg to vector because I want to engrave some woodbloks with it. In fact, with the negative of the image... These are thick paintbrushes, and I don't need to engrave only the wireframe - I want to have solid, thick lines of engraving.

I am using X3, but I realised it's not working fine because I don't get a negative when I invert the image. I get too many objects I think

 What I did was vectorizing, then converting to bitmap at 1200dpi, then vectorizing again. Crazy I know. Anyone has a better suggestion?