I am using 100% cotton coats & clark art v31-K8 470 T-39--just ordinary thread...quilted almost half of the quilt til I started having this problem...now one needle breaks after another...have tried adjusting bobbin tension..that didn't work..adjusted everything I could think of..and it won't get back to normal...Will try a bigger sized needle...have to buy some later this week... thanks for all your suggestions...! Bette Jo in Yreka, Ca..