Prism99

I like Aurifil 50wt cotton thread for piecing. Presencia is supposed to be fabulous for piecing also. I would be leery of using 70/80/100wt thread for piecing for a couple of reasons. The most obvious is that such fine thread may not be strong enough for piecing. Also, wt is not the only vital attribute of thread; you need to consider such things as fiber content and manufacturing process as well.

I have some 100wt silk thread which I know some quilters use for very fine and detailed quilting; it would not work at all well for, say, quilting lines 6" apart on a quilt as the stress would be too much for the thread. With quilting lines 1/4" apart, it works great. Piecing requires a stronger thread, especially if a quilt might not be very closely quilted, as there will be stress on the seams when the quilt is washed, when someone sits on it, etc.

Fiber content of piecing thread is important to me too. I absolutely love polyester thread for quilting (I use Glide a lot) because it adds a bit of shine and sparkle to my quilting, plus it is strong and can handle high speed sewing. It works well for embroidery machines too. I tried polyester thread for piecing and found I don't like it as well as cotton. For one thing, it is slippery compared to cotton. When chain piecing, if I don't leave extra space between pieces using polyester thread, the thread has a tendency to slip out of the fabrics ends after I cut it. I have read that polyester thread works better for piecing if it is used only in top or bobbin, with the other thread being cotton. This is because cotton "grabs" the polyester so you don't have as much of a slippy problem with it. However, I found that using cotton thread in both top and bobbin gives me the easiest and best results because I never get the thread slipping out at the ends no matter how closely I cut it.

As I mentioned, I like Aurifil 50wt cotton thread for piecing. I like using a size 75 or 80 needle with this thread. I like the smaller size 70 needle for machine applique, but I like a slightly stronger needle for piecing because I am going much faster and do not want to inadvertently bend (and break) the needle while going at breakneck speed.

If you were to use the finest needle (size 70) and finest thread (size 100wt) for piecing, I think you would want to piece more slowly just to make sure that the needle doesn't get bent out of shape. I hate having a needle break in the machine as, not only could a broken piece fly into my face, it can take a sewing machine out of time so it needs repair.