what threads are you trying. For me I had just about every thread break that was cotton except for king tut which is long staple egyptian grown cotton. Also had more success with poly. I had practice off and on for about 4 years and just recently with the help of craftsy classes just started to have some success. I recommend a topstitch needle and using poly or if you really love cotton king tut is the best of all brands IMHO the only one I haven't tried is presencia but all the others had shredding. Topstitching needles have a wider hole and groove for the thread which causes less shredding. Some of the breakage can also be due to moving the sandwich too fast. Don't give up, I almost did and finally it just clicked and I feel it will for you too if you give it some time