I was doing a string star block and was frustrated because I could not get the "Y" seams to be perfect. I then read on the internet to first sew the stem of the "Y". Then put a pin into the triangle where the "Y" seam and triangle patch come together and sew from the outside edge into the stem. Place your needle down where the two seams meet. Turn the fabric and sew a couple of stitches. DO NOT BACKSTITCH as some machines take a stitch before they start back. Repeat on the other side. I found that this method worked perfectly for me. Hope this is clear.

You've gotten great advice that I can't add to already on the Y seams. As to general accurate machine piecing, I suggest starching as well and slow down. Some really finicky blocks are better just done with paper piecing. General piecing, however, certainly aim for that perfect 'scant' 1/4" but more importantly (to me) is being consistent with your seam allowance.

As to starch, I use the liquid Sta-Flo brand and mix to a 50/50 solution with water. Let the starch (regardless of type you use) to soak into the fabric a bit before pressing/ironing. A - it makes the fabric stiffer and B - you don't get flakes.

Good luck with your challenges.

Kaye Wood (no relation) has a tutorial on doing it this way. I don't remember if she pressed the first seam open or not, but I would think that would be the thing to do.

I learned how to make tumbling blocks without "Y" seams. So much more fun.

I really like Kaye Wood's tips and techniques. Here she demonstrates her method of doing a Y seam. I used this making a quilt that had tons of Y seams in it and it worked like a charm.

https://www.youtube.com/watch?v=XLkHfcuNzCA

She has lots of other tips on being accurate as well.

To get my points to be pointy in a pattern (like in triangles, stars etc) I put a pin through the point and then through the fabric I'm sewing it to. Most of the time it is 1/4" but not always as often there is just enough give in fabric to be a little off at that intersection. I make a mark on my fabric that I'm sewing the point to with a Frixon pen where the pin comes through and that is my seam guide when I go to sew my pieces together. Perfect points every time. Even if the seam on the backside isn't perfect who will notice.

I avoid them like the plague, but if I find myself having to do them, I just mark the 1/4" dot and sew starting at the dot from both directions. For some reason, this works for me.

I'm so grateful for all the suggestions and links. Kaye Woods does a great job of simplifying that pesky block.

All I can add to this is when you get close to where you want to stop, if it doesn't look like it will stop in the right spot, shorten your stitch length, this has worked for me anyway!

Good one, Tartan, LOL.
Me too.

It helps if the pieces are the right size to start with.

Sally Collin's book is tops for precision piecing. Yes, I do use Magic Finish purchased at Walmart for less than one dollar. I like to put the finish on sections of fabric prior to cutting. A light touch with the iron to press, not iron, will make all the difference in the world. Good Luck!