Having problems with half square triangles
 

When I sew 2 squares together to make half square triangles somehow I lose the 1/4" seam allowance, what am I doing wrong. Hope this is clear

Maybe a picture will help. I bought one of those F&P rulers so you just line up the center line with each corner, then draw a line on each side of the 1/4" wide ruler. Then you sew on each line and then after pressing and trimming, you have two perfect HST. This is what works for me. I hope that you can find l work best for you. Have you tried the paper triangles called Thangles??

Bbeyes, I am wondering if perhaps you are sewing your stitch line on the diagonal line from corner to corner?? The center diagonal line should be your cutting line, not your stitching line. In other words, if you draw a diagonal line from corner to corner on your square, you should stitch two lines 1/4" on either side of your drawn line, then cut directly on your drawn line. Maniac's picture shows this.

I have one of those rulers and use it the way Jeanne suggested.

Oh, I must be brain dead or something as I can never get them to come out perfectly. Seems like I've tried everything and the only thing that gives me a perfect outcome is paper piecing. I've come to accept that I may never be the perfect quilter and now I don't stress out over it any more.

Sometimes it is best to draw your lines. The center ( cutting line) and the stitching lines on each side of the cutting line, 1/4" from the center. Then, pin if you need to in order to hold the pieces together. Slow down your stitching. The few minutes it takes to do the prep work can help a lot! With time & practice they will become easier & easier ( and more precise)

Even with the diagonal lines, etc. - I still have MUCH better results when I cut the squares one inch larger than when I cut them only 7/8 inch larger than the finished size.

I need to trim the HST units - but by only a few threads. When I cut the squares only 7/8 inch larger, the HST units almost always turn out skimpy.

http://www.mqgvictoria.com/2014/06/hst-tutorial.html

My Guild did a charity project using HST. The above link takes you to the various tutorials we had for making the HST blocks. I used the one that made 8 at a time. I did oversize my blocks and trim as I am not accurate enough to have 8 come out perfectly. I think I started with my original squares 1/2 inch larger.

By making 8 at a time the bias was on the diagonal seam and the outside edges were straight of grain.

I use the disk Triangulations. I love it. It makes it so easy and exact!

I make them bigger and then use my loc-bloc ruler to trim them down to size. I can never get a decent hst using exact sizes.