bkay

On the disappearing blocks (4 patch, 9 patch) how do you figure the math so that you can make a specific size block?

For instance, a disappearing 4 patch has 3 seams across and 3 seams down. If you want a 12.5" unfinished block, you would take the 12.5 and add 1.5" to the block for seams, which would give you 14". Then, you would divide the 14" by 2 which would give you 7". Is that correct?

What if the cut is on the diagonal? Does that make a difference? Do you just count the seams? Is it that simple?

bkay

rryder

Hey Bkay- that sounds right, your 4 7” squares would make a 13.5” unfinished 4patch, then there would be two more seams across and down when it’s cut and rearranged so that would require another inch for seam allowance giving you 12.5” unfinished D4P.

No clue on the diagonal, my impulse would be to oversize the initial 4patch block by a fair amount (for me that’d be around 3 inches or more just to be safe) and then trim it to size after reassembling into D4P. I know that doesn’t help if you’re trying to minimize waste. Would the math be the same as doing QST’s 3 times?

I have to admit when I’m playing with D4P blocks in a quilt I tend to make the D4P blocks first then make the other parts of the quilt to a size that works with the size that the D4Ps turned out to be.

Rob

rryder

QSTs 2 times, not 3. 1.25 x2 = 2.5”. If that’s the correct amount for qsts.... So, shoot for a 16” unfinished 4patch? I think I’d go bigger and trim down after reassembling into disappearing block just to be safe.

Rob

dunster

When you make one straight cut in either direction and sew it back together you lose 1/2". So what started out as an finished 12" block is now a finished 11" block.

So if you want a finished block of a given size, you make your original block 1/2" larger. To get a finished 12" block you start with a 12.5" finished block.

If your cut is not straight across or down you will lose a little bit more and are better off starting with a block that's 1" larger than what you want to end up with.

Quilt math is much easier if you always do the math in finished sizes, then add on the seam allowances.

klswift

For folks who are 'math challenged', grid paper is your friend. Draw the block on the paper, cut out the pieces and add a seam allowance. Takes a bit of time, but will help you out.

Irishrose2

I made a Disappearing 16 patch with charms, so those were big blocks to cut on the diagonal. Yours was a good question that several of us want to know.

SuziSew

I found this on google...hope the link works

<cite class="iUh30" style="color: rgb(0, 102, 33); font-style: normal; font-size: 14px; padding-top: 1px; line-height: 1.43;">www.sjqg.org/2015%20Files/Disappearing%20Nines.pdf</cite>

bkay

Actually, I was looking at one of the block swaps. It requires 12.5 unfinished. I hate making a bunch of little triangles, so was looking for interesting blocks without them.

That was why I wanted to make sure I was thinking correctly about how to make the "disappearing" blocks in the required size.

Thanks for the help.

bkay