Having trouble with combine, only some objects combine and others don't. What am I missing or doing wrong?

I've had this problem before and I can't remember what I did to get it to work. I have most of the image combined, but there are a few spots i am fighting with and they 

won't combine. They just go to the back. I've tried putting everything on one layer, I've tried numerous other things with no luck. Hoping I can get some insight here. I attached a PDF of the file. 

the white areas are what won't combine. PDF

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  • Chris is right, it's the curve directions (or fill rule) that are wrong.
    No need to weld before combining, by the way.

    I also noticed that there is a duplicate object under the biggest white object, which means that even after correction, it appears to still be black and not a hole.

    In my next post there's an explanation about curve directions and fill rules that I wrote recently in another thread.

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