another thing to think about is your hands themselves ! Do you wear mechingers gloves ( I know my spelling is off ) or are you trying to do it bare handed ? I constantly snap thread if I am not wearing my gloves reguardless of what size piece I am working on because I just do not have proper control of the fabric in certain directions ! Also make sure your hand speed stays consistent, not faster / slower in different directions or going around curves. You may need to slow your machine down when moving in certain directions to suit your hand speed