Making a printable half sphere with a cutout in it for 3D printing I made a half sphere which prints nicely. The sphere is to be used as a stencil for marking your golf ball.

I used the Knife Project to cutout the F.  This however created a lot of non-manifolded edges, which are not printable.

How can I cut out the shape and still preserve the mesh?
Once you've deleted the face you can extrude your object to give it thickness, or give it a Solidify modifier then apply. If there's already thickness you could extrude your F and use a Boolean modifier on your half-sphere.