I had a problem with what you refer to "thread stripping" and breaking on my Singer machine. Turns out that the thread was catching on the slit in the spool (used to keep thread from un-winding when not in use) and would tighten up and then break while I was sewing. I used a nail file and "removed" that slit from the spool and didn't have any more problems. Might be worth a try for you.