Seems everytime I need the formula for this method I google"John Flynn's diagonal backing" and then I have the directions. I haven't had any problems with the method the 2-4 times I have used it. I think in his instructions he recommends not using it for quilts more than a certain width. I find it a good way to stretch the amount of fabric I have for a back.

Lorna in very hot San Antonio

Thank you Mary, it was fast and easy. I'll definitely be bookmarking that one.

Mary, thanks for posting that, it's very easy to use and the pictures sure help to explain it.

JoAnne

As an update, I just received an e-mail that states:

FYI Multi-Patch has developed an online diagonal cut backing calculator thatcomputes the length of fabric needed to create diagonally cut backing forquilts. The calculator can be freely used by any quilter so please pass thefollowing link onto your guild members:

http://www.multipatch.com/html/diagonal_backing_calculator.php

It's quite easy to use!

Mary

That's a great tip about LONG stitches in the stay-stitching before the cut. Thanks!! I will be trying this technique when I visit with my sister who has been successful with it after I reminded her of the possibility. She used a 3 1/2 yard cut of fabric rather than more than 5 yards the traditional pieced way. She will be showing me how it's done as I'm a visual learner.

NancyAnn1959 wrote:
I haven't tried this yet, so am only guessing, but it would make sense to stay-stitch the backing on the diagonal, 1/4 inch on each side of where you're going to make the cut, BEFORE you cut the fabric in half.

Just remember that stay stitching only works if you use really L-O-N-G stitches, because small stitches place too much give into the seam.

Anne in Vancouver, Canada

I recently did this without any formula, however. It was just a Project Linus quilt and I had plenty of material, it just wasn't the right dimentions.

I found it very difficult!! The bias stretched and I probably made the mistake of thinking I could cut the diagonal without rulers, so it didn't turn out straight, which resulted in the backing bulging and needing to be resewn several times. I will not try this again!!

Nancy in blustery western NY

John Flynn's show airs tomorrow-maybe he'll do a demo.
eileenkny

I saved the formula so I can get the mathematically minded DH to figure out my backing from now on.

Woah--thanks DH!

My geometry teacher DH is working on why the formula works, as it was too complicated for me to figure out, but I've re-written the instructions to hopefully make them more understandable.

WF = width of fabric
LF - length of fabric needed

WQ = width of quilt back desired
LQ = length of quilt back desired

If you need to make a back that is 63 inches wide and 78 inches long and you are using fabric that is 44 inches wide, the formula would look like this:

WF = 44
LF = unknown
WQ = 63
LQ = 78

LF = LQ + LQ(WQ - WF) / (2 * WF - WQ)

LF = 78 + 78(63 - 44) / (2 * 44 - 63)

LF = 78 + 78(19) / (88 - 63)

LF = 78 + 1482 / 25

LF = 78 + 59.28

LF = 137.28, or 138 inches

Therefore, the 126 inches of fabric would not be quite enough.

Mary

Math is not my strong suit and John's formula is intimidating on first reading through the instructions. I like the idea, generally speaking, and will try this on some "junk" fabric to see how it works. I can just see myself with yards and yards of fabric cut on the diagonal and it won't fit any project. Of course, it could be salvaged as bias binding strips.

If someone tries this and could post some photos of the various steps it might make it easier for we math-challenged people, who need to see something before we understand, it would be greatly appreciated.

I think John Flynn has instructions for this method on his website - worth a look.

http://www.flynnquilt.com/workshop/FreeLessons/

Nan

I need to "grow" my backing both width and length. I have heard of a way to split my backing diagonally and then add a piece to the split to accomplish this. Is there a formula as to how big the back starts and then how big the insert is???
My quilt top is 63 x 78. I have 126 inches of backing. Can this work?
Thanks.