I sent a sewing machine to my sister 2 years ago. We used foam that we had, I had some batting she'd sent me that I knew I wasn't going to use, so that went into it. We packed it up nice and tight. Then we put a bigger box around it, packed it super tight and shipped it UPS.
It got there just fine. Double boxing is something my DH does when he ships an antique radio or 45 record player to an enthusiast. It works very well.
However, if the UPS guy tosses it over a fence because you're not home and he doesn't want to return the next day, there is still breakage. So insuring your machine is a must!