does your bobbin case have a metal backlash "spring"? If not you can add a "Magic Genie" plastic washer that will prevent backlash when you are zipping along quilting. Also, thread problems underneath are almost always top tension issues and vice versa. Don't be afraid to adjust your bobbin tension either. On my Gammill, I almost never adjust the top tension but do adjust the bottom tension when I change the type of thread. Like others, I seem to have more thread breakage with cotton than with a poly (Permacore is a poly that feels/looks like a cotton). Since you were doing fine before you switched bobbins, I'm guessing that either you have a dud bobbin (it happens, or it could be the bobbin you have in was dropped and is now "out of round") or it was wound too tight. I use a Towa gauge to measure bobbin tension--they are pricey but I've found it's worth my sanity! Jamie Wallen has a great YouTube for adjusting bobbin tension if you don't want to purchase a gauge. Good luck! You will get this figured out--a long or mid arm is just not the same as a DSM and it will be well worth it.
Also--Superior Thread has a downloadable guide for matching needles and thread (theirs--but it gives you enough info that you can figure out other brands, like Glide, etc).
Last edited by quiltingshorttimer; 12-21-2016 at 08:21 PM.