I live in Europe, and I quilt. In practical terms this means that I engage in an imperial hobby in a metric environment. This is not dramatic except when following a pattern for which absolute accuracy is called for, since 1/4" is actually 6.35mm, and who has that marked on their throat plate? Conversely, European seam allowance is 7.5mm, which is just enough wider than 1/4" to lose your points.
I particularly like the "flying geese" block, which, when made using the simple 4-at-once method (video link), demands a rather high degree of cutting accuracy to ensure that everything lines up and nothing overlaps once you're done. If there is any such thing as a "metric precut", 10cm is a common square size, and I happen to have a stack of 10x10cm Christmas precuts which I wanted to put into an "Flying home for Christmas" all-goose hanging. So, doing as every quilter these days does, I asked Pinterest. Only one hit came up. Joy oh joy, it used 10cm squares, and said that the small squares for the fast-four method should be 6.5cm. So I checked back with the seller of the 10cm squares and promptly cleaned her out of the rest of her wares in that line - which just happened to be 6.5cm. I figured this was for a reason, and sewed forth.
Peeps, Pinterest lied*. 6.5cm small squares are far too large. They leave so much overlap that two of the four geese blocks had to be ripped apart and resewn to hide the extra flappy bits. This totally defeats the purpose of a "quick and easy" mass-production method.
*shocking, I know
I salvaged my test block and got out a pencil and figured it out for real. And here it is, including process.
This website told me what metric seam allowances (SA) to add to squares destined to be HSTs and QSTs:
| HST | QST | |
| imperial | 7/8" | 1.25" |
| metric | 2.5cm | 3.5cm |
And this blog helpfully posted the algebra for figuring out the cut sizes:
if
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x= finished height
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y= finished length
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z= cut size (small or large)
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then
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x+(HST SA)=zSmall
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y+(QST SA)=zLarge
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when
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zLarge = 10cm
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(our known pre-cut size)
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y+3.5=10
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y=6.5
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thus
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x=3.25
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(as flying geese are 1:2,
height:width)
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and
so
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3.25+2.5=zSmall
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5.75=zSmall
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Hallelujah, we have a working hypothesis! For Fast 4 Flying Geese in metric using 1 large square @ 10cm, you'll need 4 small squares @ 5.75.
A test block has revealed this to be accurate. But perhaps too accurate; due to the vagaries of bias, I have found that a generous 5.75 or even 6cm retains your points and allows a nice square-up trim.
I have typed this up around the evening chaos and meal, and now I need to hit Publish so I can go read bedtime stories. If I think of it, I'll upload photos for those of us who need to see this stuff before it makes sense.
