TO start let me say that myself and my lead mechanic have both given this machine the once over. Its a Juki LU-1508-N. I am not sure what is causing it to skip. we have retimed the hook and needle and by the shafts, new needles, we have replaced the hook and nothing seems to be working. Could a spool of thread that is wound too tight be the cause of it? The leather we sew is not very thick it vaires from 3 oz to 6 oz. Any tips would be greatly appreciated.