I have broken a needle or two by forgetting to change the foot when I change the stitch. Thankfully I have not knocked off the timing in doing so although I know that is possible. The only machine I ever broke was my serger. While threading it, I had accidentally wrapped a thread around something it shouldnt be around, and when trying to make it chain, I broke a looper and knocked the timing off. Realized immediately what I had done wrong. My repair guy appreciated my honesty (so he didnt have to hunt for the cause of the problem) when he asked what happened and I told him "operator error"