Question re Quilt Top Blocks Set on Diagonal
 

This will be an easy answer for most of you: I dug out an old UFO to finish. The blocks are made using 50's fabrics and older and most of them finished at 5-3/4". I'm not sure why they are irregular finished sizes -- I'm much more particular now having more years of experience behind me. But I want to finish it since I like the fabrics and the pattern. Since this is the first quilt I've done set on the diagonal, my question is: how do I figure out the size of the triangle piece that goes on each end? Let me know if you need any more information.

Thanks so very much.

Fran

This should help you.

http://quiltville.com/onpointmath.shtml

Thanks for the tip! I should have remembered Bonnie's math -- I read this several years ago! Well, that's why I asked the question to begin with -- my brain doesn't work these days worth a . . . .

I bought this ruler which does all the figuring out. I also like to make them larger so if you want the quilt to float before your first border, it is done automatically. You can trim it if you want.
http://littlefoot.net/product/the-setting-triangle/
So many quilting notions that Lynn Graves created.

When I have blocks that are not "exactly" the same size and I am putting them on point, I make the triangles larger than needed and then make the "new" blocks the same size. This corrects the irregular size of the original blocks and is not noticed unless measured. I make my triangles by making a square the size of the original block, in your case I would make the square 6" to cover all block sizes, then cut the square into two triangles. This method may not be the precise method used by advanced quilters, but it works for me. Good luck.

Here is a little bit of information that may help. The link that katier825 shared tells you the size square to start with depending on the finished size of the block. The first time I made a quilt that was set on point I had a wonderful teacher that explained why the setting triangles need to be cut differently. If "the why" is explained so that I can understand the reason, I am able to figure out the size.

The thing to remember when setting any quilt, whether you are working on a horizontal quilt or a quilt on point, is you want the "straight of grain" to be along the outer edges of the quilt. You do not want a bias cut along an outer edge. Bias cuts are more apt to stretch than "straight of grain" cuts. To achieve "straight of grain" along the outer edge, you will need to make two differently cut triangles.

To make the side triangles, you need to use a square cut diagonally twice using an X from corner to corner. That puts the hypotenuse of the right triangle (straight of grain) on the outside edges. Since you will get 4 triangles from each square, count how many triangles you need and divide by 4. Round up if needed. For your block that you say is 5 3/4", I would start with a square that is 9 3/4" or even 10". Cut diagonally corner to corner both directions (cut like an X) making 4 triangles from each square.

To make the corner triangles, you need to again have the "straight of grain" on the outer edges. To do that for the corners, you need to cut your square the size you need and cut once from one corner to the opposite corner on the diagonal. Since you will get 2 triangles from each square, you will need to start with 2 of these squares for one quilt top. You will now have "straight of grain" on all the triangles around the outer edge of your quilt. For your 6" block, I would start with 2 squares that are 5 1/4" or 5 1/2" each. Cut diagonally one time from upper right corner to lower left corner. After you have all your triangles sewed in place, you will need to trim remembering to leave the 1/4" seam allowance at the points.

I purchased Fons and Porter's "Easy Diagonal Sets" ruler. Its one of my favorite rulers. You do not cut squares you cut strips of fabric and cut your triangles by lining up the ruler on the strip. The markings tell you what width strip to cut for whatever the size of your finished block is. There is not math to do and you do not need to worry about straight or bias of fabric because all that is 'automatically built into the ruler'. One end of the ruler is for the side triangles and the other end is for the corner triangles. Works for from 3" to 12" finished size blocks. (I also like the easy to read yellow markings.) Its a real no brainer ruler and I highly recommend it.
*** Fran, I notice you said the blocks finished at a certain size. When I said the ruler gives the size for the finished blocks I mean the final size they will be when sewn into the finished quilt. So for example if your block currently measures 5 1/2 your finished block size would be 5". That's the size you look for on the ruler. If your block ends in a 3/4" you would round it up to the next full inch then deduct the half inch seam allowance to get the finished size of the block to choose. This ruler gives a generous amount to the triangles you cut so they will be over-sized when sewn in, allowing you to square up the quilt without cutting into your seam allowances. I hope this makes sense. Feel free to PM me if you want.