I have a 6" square. I cut it in half diaganolly (sp) and sewed two halves together. My instructions say to square it up to 5 1/2". How do I do that? If I cut one side it will be uneven. I just want to know how to square it up and still be even.

http://www.youtube.com/watch?v=OQq-5p8RCS8

Here is one video that demonstrates it. If it isn't clear after this one, Google "how to square up half square triangles" and it looks like there are more videos explaining it. I didn't watch the other ones. You have to use a diagonal line on the ruler lined up with the diagonal seam of the half-square triangle. If you don't have a ruler that is exactly the size of the finished HST then you will have to cut a little off of two edges then adjust the ruler to cut the rest off of the other two edges. There is a ruler that is called Precision Trimmer, that is for squaring-up and most LQS's have them.

I'm sure there is someone on the board who can explain it much better than I can and hopefully they will read this post.

line the diagonal line of square ruler up with your diagonal seam...adjust the ruler so that a smidge is sticking out on one side and top making sure you have a smidge more than 5 1/2" showing on the other side and bottom...trim that first side and top; turn the block 90 degrees, line up diagonal again- line up 5 1/2" marks on the freshly cut side and bottom and trim the remaining side and top.

You've lost me here.

What sprang into my mind was a clear block the size of the finished block, with a line down it from one corner on top to the opposite corner on the bottom. Line that up with the sewed line and cut around the clear block.

Would that do it?

Whoops....that mythical clear block should be the size of the
finished block, PLUS the seam allowance on each side.

You would have to have a mythical clear block for every size block you might want to square up. The Precision Trimmer has the diagonal line and has numbers for the specific block sizes you want to square-up to. I know that makes no sense but the ruler has instructions and I'm sure someone at the LQS could explain it.

Do you have a plastic square ruler made for rotary cutting fabric? If you do, most of them have a 45º line on them that you place on the sewn line and then trim around the edges, making sure you have the 5-1/2 inch measurement under the ruler. If you don't have a plastic ruler, you can still trim your block but it will be more difficult. Take a piece of cardboard (cereal box) and measure and cut a perfect 5-1/2 inch square. Place your cardboard square on your block, lining up the two corners of the cardboard square with the sewn line edges showing on the corners. Mark all around the cardboard square with a pencil and then cut out your 5-1/2 inch block.

If my math is correct (its still eary so it might be wrong) this is IMPOSSIBLE! To make 5 1/2 inch UNFINISHED half square triangle you would of had to START with a at LEAST a block that measured 6 3/8 (6 1/2 if your gonna square it up) Since you started with a 6 inch block you can only square this block up to 5 inches.

The formula for HST's is to add 7/8" to the FINISHED size (if you're using the exact method).

That breaks down to 1/2" for the seam allowance and 3/8" for the angle.

So if the goal was a 5" FINISHED HST (which I think it was), starting with 6" squares leaves just a tiny bit of extra fabric to trim down the HST to 5.5" UNFINISHED.

This is also how I do it - just finished 80 x 4" blocks for a border! I first read it on Quilt University, which explains quite well, with pictures. Under section called "Glossary" which is in alphabetical order.

That's what a Square Up ruler is for. They don't have too many markings and make it easy to center whatever block you are trying to square up.

Yes, you can use any ruler that fits and has the 45 degree angle from the corner. But, the Square Up rulers have only the markings you will need to use.

ali