I did a search for your model it appears that at least part of the upper threading is similar to the Franklin Rotary. It appears similar to page 7 of the pdf that you can get from ismacs.
http://www.ismacs.net/domestic/manua...anual-1926.pdf - That seems to be at least a better image of the threading. That is the one I used and had to
read it several times & try it several times before it finally "clicked" (both actually and figuratively) to get one of the Whites threaded.
While searching, I also saw that there is a youtube video of threading that particular model, but since I'm on dial up - I don't know how good it is or if it would help you. I also saw that sewusa.com has a threading diagram for 117.591 I think there should be a little wire spring/eyelet (behind the flat metal piece) that it needs to hook into before coming out at the top and seems to have a definite sound when it catches it.
Janey - Neat people never make the exciting discoveries I do.