Snowball and square in a square blocks
 

I have trouble with piecing these blocks. The corners never come out right. I usually have to unsew and do again. Does anyone have any help they can share?

If you want easy-peasy no-fuss and worry free precision .......
paper piecing is your answer!

Otherwise ....... practice practice practice!
While paying heed to your precision in cutting, marking and stitching.

Hope this doesn't end up as multiple repeats, seem to have a bit of an issue posting today.

My solution is to cut large and trim to fit. For either the snowball or the Square in Square, your center square would be cut correctly/precisely. The setting triangles would be cut an extra 1/4-1/2" larger than called for. So for example, if the directions call for 3" squares cut in half along the diagonal, I'd be making a 3.5" square. Slap them on easily and then use a ruler or template to trim to the correct size. For me the sewing goes so much faster the trimming doesn't add any more time than being precise in the first place -- but my accuracy is better! Plus, I was already handling/checking my subunits and decided I might as well make it worth the time.

20-30 years ago I'd probably give an audible sniff in disdain over "fabric wasteful techniques. I've watched and done tests and the extra 1/4-1/2" I add has usually never needed more than an extra row of whatever width of fabric. Now I consider the speed and ease and accuracy well worth a tiny bit of fabric, and when using strip cutting techniques there are always bits of unused fabric anyway.

Plus, 20-30 years ago I didn't have the vision issues I have today. For me, cutting big and trimming down is the solution.

I do this method too and yep. Do not sew on the line for those little squares. Reason is the thread and the folding of the seam use up a bit of fabric and if you stitch right on the line, your little corner triangle will be too small to line up with the larger square. I would actually make a few test snowball blocks, you may have to stitch that seam even a little more to the outside edge depending on the thickness of the fabric and the thread. If the blocks are not that large, I may even not trim the waste corner triangles off as I will use the edges of my larger fabric to guide my seam lines as my piecing will be a bit more accurate that way. Leaving those waste triangles usually doesn't leave too much additional bulk if it is on smaller block

I do as Tartan does. I make my square in a square blocks this way, too,just a modified snowball. when you sew along the marked diagonal line, make sure to sew next to the line, not on the line.
I don't have waste with this message because I sew an additional diagonal line about 1/2 inch away from the true needed line. It gives me a bonus half square triangle that i can use either in the quilt border, on the quilt back, or in a random scrap block.

I might be a strange one, but I can never get the method of sewing a square over the corner to work out. I have to cut the diagonal and sew a piece on and then trim to size. I use my easy angle ruler all the time for blocks like this.

I even drew up a set of square in a square blocks so I'd know what size to cut the inner square. Then I sew slightly oversize triangles on the corners and trim them to the exact size. Only way I can get them to turn out correctly.

Marcy J, I am so glad you asked this question. Such a simple-looking block, but I can never get them to come out correctly either, so I have avoided patterns that called for them. I am going to try all of these techniques!

I’m a broken record here but I use Deb Tucker’s Corner Pop tool for snowball blocks and Square Squared tool for SIS blocks. I know a lot of people don’t buy specially tools or rulers but the accuracy I get with her tools is worth the price to me.

The ruler is half off at this site https://www.quiltingstencils.com/Deb...op_p_3739.html