First check the screw by taking it out and rolling it across a flat table. If the screw flops around there it is a sign that it was not straightened after grinding. If the screw is not straight there is not much you can do to help except straighten it. Even with a relatively straight screw, if it is only supported on one end, you'll be limited to how fast you can turn it. Supporting the screw on both ends, under a bit of tension, will help keep it from whipping.