Trimming Curved Blocks
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Have you ever finished a bunch of curved blocks, then realized they were slightly too small? Or a bit wonky? Or didn’t quite have the seam allowances in the right place? These are all very common problems!
Rather than allow these normal pitfalls to ruin the fun of curves, I like to create my templates with some trimming room. Read on to learn how to trim your way to some pretty darn perfect curved blocks. This method will work with both half circle and quarter circle blocks.
What You’ll Need
You’ll need a standard ruler and a rotary cutter. If you happen to have a rectangular or square ruler that is the same size as the block size you’re trimming to, it can be a great tool to help you visualize where your trim lines will be! This isn’t necessary though.
A Note About Seam Allowance
There are two kinds of curved blocks that are important to be able to distinguish between when trimming: Blocks that should finish with their curved pieces on the edge of the block, and blocks that do not have curved pieces extending to the edge of the block.
(A quick definition: Finished refers to how the block looks and measures when it’s sewn into the quilt. So, a finished block of this type would have the curved portion going all the way to the edge of the block. The unfinished version of this block would have a 1/4” seam allowance between the edge of the curve and the edge of the block.)
Check out the below examples of finished blocks. The block on the left does not have the curves extending to the edges of the block. The block on the right does, which means a little bit of extra care is required when trimming.
The example I’m using in this tutorial is a block that does have the curve extending to the edge of the finished block. This means we will need to be extra careful that we trim to leave an exact seam allowance around this block.
Let’s Get Trimming
Side 1: For a block that does have curves extending to the finished edges, we will trim the top edge first. Center your block on your cutting mat, then lay your ruler on top so that a 1/4” ruler line runs directly over the top of the curve as shown. Trim along this edge.
For a block that does not have curves extending to the finished edges, first trim the flat bottom edge shown in the next photo, then the curved side. Trim as close to this edge as possible!
Side 2: Now, for both types of blocks, line up the edge you just cut carefully on your mat. Then, trim the other vertical side at the desired unfinished block size indicated in the pattern.
Side 3: Line the trimmed edges up with the lines on your cutting mat to trim the sides, centering the block horizontally so you can easily tell the width of the block. For a block that does not have curves extending to the finished edges, this step is easy! Making sure the block is centered, trim each edge evenly so that the block now measures the desired unfinished trim size mentioned in your pattern.
For a block that does have curves extending to the finished edges, you’ll need to be a bit more careful. Line up your ruler again so that the 1/4” line is right along the curved seam, or a hair over.
If you look very closely, you should hopefully be able to see 1/4” vertical tick marks on your rulers. If you look at the to left corner of the 1/4” red square in the image below, this is where the the edge of the finished block will actually fall once all of the seam allowances are taken away. Because the curve is so gentle, we should be able to trim just as we have our ruler lined up without losing a noteworthy amount of the curve, but it’s worth checking that before trimming.
Side 4: Now, flip your block and trim the other side in the same manner, first ensuring that the trimmed block measurements will be correct!
And there you go - you should now have perfectly sized and trimmed curved blocks, and a more accurate quilt top once you’re finished! If you’d like to view this tutorial in video form, you can do so below.