Dealing with the elusive 1/4" seam...
 

I'm relatively new to quilting (and sewing for that matter). I enjoy the process of designing, cutting, piecing etc, but I have a dickens of a time keeping things matched up as my blocks grow. I am certain that most of my problems have to do with my inconsistent 1/4 seams. I've bought and tried various 1/4" presser feet, used diagonal seam tape, tried the magnetic guides etc, and still haven't zeroed in on the "perfect" seam allowance.

I'm sure I just need tons more practice to get it right, but in the meantime I am dealing with blocks that are less than perfect. I've recently read https://www.kimberlyeinmo.com/the-el...-and-conquered and sounds like maybe I should shoot for the scant 1/4" instead of the perfect 1/4".

I do my HSTs by the 2-at-a-time method (over-sized), then use a ruler to cut them to the exact size. Maybe I should make everthing oversized and cut to size? What tricks can I use to make my 12.5" blocks be 12.5" blocks when I'm done?

Good day to you! I had some problems with my 1/4 inch seam allowance and like you tried all the same tricks. I finally had an aha moment and realized that my 1/4 inch seam became wonky at the end of the seam and when going over seams putting blocks together. My machine is a zig zag, decorative stitch, and embroidery model. When I put a 1/4 inch foot on it, the foot would only cover the left feed dog and did not cover the right feed dog. I put my straight stitch foot back on (the one that covers both feed dogs), moved my needle to the right, and fixed the wonky seam problem. Hope this helps.

Yes, I discovered the feed dog problem when I put a 1/4" foot on mine (I tried several different ones). Unfortunately, I have an older machine that doesn't allow me to adjust my needle side-to-side. So far, I've found the diagonal seam tape with my regular zigzag foot gives the most consistent result for me. But my blocks still come out too small.

If you measure the seam allowance and it seems ok, maybe you're not pressing correctly. That can affect the size of the block. Are your seams lying nice and flat?

hugs,
charlotte

If your unit is ending up the size you want it to be, that is what matters.

Fabric prep before cutting is another discussion. Some unwashed fabrics will shrink when being steam pressed.

Back to seam allowances..

Try cutting four strips of fabric 8.5 x 2.5 inches.

Sew the strips together using "your" 0.25 inch seam allowance.

Press the unit however you prefer. Pressing seams to the side or pressing them open is another discussion

Now measure the size of what you have.

If it ends up being 8.5 x 8.5 - your seam allowance is "perfect"

If it ends up being 8.5 x 8.75 - uou need to make your seam allowances deeper/wider

If you end up with it being 8.5 x 8.25- then you need to made the seam allowance narrower/ shallower.

This testing/practice is a bit of a bother, but can minimize frustration down the road.

Where variations can occur besides the seam allowance width:

Some threads take up more space

A heftier fabric takes up more space where the fabric turns at the seams

overly entusiastic ironing/pressing can distort the piece

Even measure the actual size of your cut pieces!

"My" 2.5 x 8.5 piece is actually a tiny bit larger than 2.5 x 8.5 inches because of the small space between the ruler and rotary cutter and how I place my ruler.

The more pieces involved, the more chances for differences to accumulate

I have taken index cards with 0.25 line ( or graph paper with quarter inch grids) and sewn on that to figure out where to line up the presser foot with the edge of the fabric.

It might be helpful when cutting to keep the ruler line inside the fabric rather than outside. Sometimes that gives you that tiny bit extra.
Hope that makes sense from my pre-coffee brain!

Another thing to consider is that some of the newer modern machines with very wide feed dogs can mean the fabric is only going over one of them which can make things wonky. Some machines don't have a changeable stitch plate or a way to adjust the needle to the left or right. Agree with the method bearisgray posted about measuring the finished piece. May have to make practice piece for each project if the fabric/thread combo is different. If I am making something with no points and perfect accuracy won't affect the finished project, I just roll with "close enough", and make sure everything is the same amount of "close enough". A nine patch or similar for example is very forgiving.

Most of us have had to go through a learning curve for what works with our machine(s).

A reminder - if you change your machine or use a different ruler - and you are in the middle of a project - to verify that things are matching up to the previous work.

The current project I'm working on uses blocks of 9.5" x 9.5" ((churn-dash). On the square units (HSTs and half-squares), I'm pressing seams open and I think they are lying nice and flat. I tried a couple of blocks pressing the row seams to the side, but I think I prefer pressing open.

The blocks end up being about 9.25" and the edges are not quite even. Great suggestions bearisgray! I will try those.

I'm pretty confident that my cuts are acurate, And since my HSTs are cut to 3.5 x 3.5 after sewing (and my center block is 3.5 x 3.5), I suspect I'm off on my half-squares The suggestion on the strips will probably help me. I might try a narrow seam on those and then cut them to size.