We've been talking to a lot of quilters lately who have been complaining about piecing issues.
Their pains are about blocks not coming out the correct size and points being cut off. We recommend that every quilter do a seam test!
Do a test often, especially when you've had your machine serviced or are working with fabrics that you are unfamiliar with.
Cut three strips of scrap fabric 2" wide by 10" long. Sew two of the strips together along one long side, using what you believe is your good 1/4" seam.
Be sure the strips match exactly on top of each other and sew consistently down the whole the length of the strip. Press the seam to one side.
Add the third strip in the same way, sewing down one long side. Press the seam to one side.
Now, measure the strip set you just made. The set should be 10" long, 5" wide and be square and consistent. The center band of fabric should measure 1 1/2" wide over the whole length of the strip.
If the set is wider than 5", your seam allowance to too small. If the strip set is narrower than 5" your seam allowance is too fat.
Keep making new strip sets until you find the perfect 1/4" seam for you. It will be worth the time and effort!
**EDIT: We received a great question - Could you please also explain how servicing would affect the seam outcome?
A good service technician should make lots of adjustments to your machine. Over time your machine could lose it's accuracy, and you'd probably not realize you're making adjustments to how you sew to compensate. When it gets serviced, the technician will put it back to the true 1/4" seam.