Many machine quilting instructions tell you to bring the bobbin thread up through the quilt and stitch in place for a few stitches. Then continue to free motion or straight line quilt using an even feed foot. When you stop to position your hands the first time, you may clip the tails at the beginning.
When you come to the end of your quilting end the quilting by stitching in place to secure the stitches. You would then clip the top thread and the bobbin thread as you don't want to leave threads on the back to get tangled in your next quilting. This method takes a little longer but keeps the threads from making a little clump of knotted thread on the back of the quilt.
There are several ways to stitch in place. When using an even feed foot, you turn your stitch length dial to zero to stitch in place both at the beginning or the end. When free motion quilting simply hold the fabric in one place for a few stitches before beginning to move the quilt for quilting. At the end of free motion quilting again hold the fabric in one place for a few stitches to lock the thread.
Some quilters prefer to simply back stitch. You may backstitch when quilting free motion or back stitch when using an even feed foot. Either way it will lock the beginning and end of the stitching. The problem with backstitching is the stitches are more visible than stitching in place.
Some brands of the larger throat short arm quilting machines have an automatic thread cutter. If you have one of these machines you might find that it is not necessary to bring your bobbin thread to the top. You may just stitch in place to lock the stitches at the beginning and end. When you finish quilting an area you simply lock the stitches by stitching in place or back stitching and touch the thread cutter button to cut the threads and simply move to the next area of quilting.
The method for knotting thread in machine quilting is a personal preference and each quilter needs to make her own decision concerning this. For an heirloom quilt you might want to bring the bobbin thread to the top. For a child's quilt simply backstitching may be all that is needed. Whatever method you choose it is necessary to secure the stitches at both the beginning of quilting and at the end.
There are several tricks for chain piecing triangles that might be helpful to keep the machine from "eating" the fabric corners. Before you begin stitching, hold the top and bobbin thread out behind the pressure foot. This will help keep the thread from tangling at the beginning of your patches.
The simplest way to avoid trouble at the beginning of triangle piecing would be to use a leader patch. If there is a scrap quilt pattern you like that is made from simple squares -- such as the nine-patch -- cut squares of scraps to a pre-determined size. Keep them near your machine in a small container. When you are beginning a new group for chain piecing -- first stitch one of your scrap sets of squares. This square patch would act as a "leader" to the triangle pieces. At the end of your triangle pieces stitch another set of "leader" squares and leave it on the machine -- cut your triangles away. Next time you sit down to sew your "leader" will already be stitched and you can begin with triangles again. After several stitching sessions you'll have several scrap blocks completed using your scrappy squares.
Another alternative would be to purchase a straight stitch needle plate from your sewing machine dealer. The zigzag machines have a needle plate with a wider opening and when piecing the needle tends to push triangle points down into the opening causing those small and crooked stitches. If you need to zigzag be sure to remember to the throat plate so you don't break needles.
Also you could try using a stiletto, the point of a seam ripper, a bamboo skewer, or any other pointed tool to guide the first few stitches of a new pair of triangle patches. Many quilters use one of these tools and have good results feeding the fabric under the pressure foot.
Cut your triangles with the Easy Angle Tool. This triangular shape acrylic tool is made by EZ Quilting by Wrights. It is available at quilt stores, chain fabric stores and discount super stores. With this tool the triangles are cut from strips rather than from squares. When using the tool, the "dog ears" on one edge of the triangles is already eliminated. "Dog ears" are the little tiny triangle points that are usually trimmed off after stitching. These triangles are cut from strips and the "dog ears" on one end of the triangles are eliminated with cutting.
When chain piecing these triangle sets, send the corner without the "dog ear" through the machine first. You can feed them through one after another by butting up beginning point with the missing dog ear to the previous triangle end that still has the "dog ear".
If you do a lot of chain piecing you might want to invest in one of those little stands that hold a seam ripper upright. There are two or three different companies who make them. When you finish chain piecing a long string of patches, simply hold the patches with the chain between over the upright seam ripper and pull down into the cutter to cut the thread. If you wish you could make a seam ripper stand -- simply glue an empty thread spool to a base -- such as a block of wood. You just need something to add a little weight to the empty spool. Place a small seam ripper upright in the center of the spool -- glue if necessary.
There are some "point trimmer" acrylic tools available to purchase at quilt shops. There are two or three different styles but they all are used in a similar way. These tools line up on the rotary cut pieces and tell you where to trim the "dog ears" before stitching so they won't be there to get caught in the throat plate of your machine. The trimmed patches are easier to line up and are very useful in some applications.
Please don't be discouraged about piecing triangles as with anything a lot of practice will improve your piecing skills. Remember that "finished is better than perfect." Enjoy your quilt making.
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Squaring Up And Trimming
When I am piecing a block I try to cut all pieces as accurately as possible. Then I stitch them as accurately as possible. I try to use a "scant" 1/4" seam allowance. When the seam is stitched and pressed to one side there is a slight amount of fabric lost. On some blocks, especially those with many intersections, I find it is more accurate to press seams open.
In many years of piecing quilts I have never "squared" my blocks. I leave them as they are and stitch them to the sashing, setting squares, or to the next block. If there is a slight variation on the edge of the block it is not visible when the blocks are stitched to each other, to sashing or setting squares.
The only time I trim and "square" is when a pattern instructs me to cut fabric larger than needed and stitch. Then "trim and square". If I get one of these patterns I am more likely to re-draft the pattern and make it accurately than to cut pieces oversize and stitch and trim. I prefer to be more accurate throughout the process rather than trimming excess frequently.
The drawbacks of trimming and squaring blocks are the possibility of loosing points or part of your block that you need to make your block correct. If you trim too much in squaring when the block is stitched into the next seam something might be missing and would be noticeable in your finished quilt.