Squaring up a king backing
 

Advice is needed. I have a king size flannel backing for a quilt. I seamed my 3 lengths together (40 inch wide each) without squaring each individual length. Now I've got a king size backing that needs squaring. I'm stumped. Help!

I agree with Tartan. Square it up after quilting it.

My quilter requires the backings to be square so I need to square up the backing. I do square before binding. I ended up using a large 15 inch square ruler and my 8x24 ruler (Thanks Tartan) and squared it that way but not sure it is entirely square. Guess I'll go with what I have and see what she says.

Edited, it is at least the same length on both edges when folded in half so guess it will be OK. LOL!!

If you have a spot that you can lay it out completely, take a looong tape measure and measure the distance from point to point diagonally. If they are the same (or at least close) then your backing is square. This is a trick that my DH (a woodworker by hobby) taught me and I used it all the time.

Oh boy, I hope you checked with your longarmer for how much excess she needs to load it on the rack. I can tell you I need more than 3" to 4" on every side. My minimum is 5" on every side but prefer 6" if I can get it. Additionally, many longarmers prefer all selvages be cut off. They are a different weave and weight and some react differently and can cause needle/tension issues. They also shrink differently so once washed an unsightly pucker could form.

I know this will make a lot of people cringe but I rip my backing pieces, both lengthwise and crosswise.

Ripping and squaring up after doing so will ensure your fabric itself is on grain.

I also rip. I can get a much straighter edge that way.