Hi Guest, Welcome to the quilting forums, register now —or—

Page 1 of 5 123 ... LastLast
Results 1 to 10 of 43
  1. #1
    Prairie Pointer

    Join Date
    Jun 2015
    Location
    Carrollton, TX
    Posts
    54
    Post Thanks / Like

    Default Understanding seam allowance-from a mechanical engineering perspective (new guy)

    Please help me understand seam allowances. I have been told to use a 1/4" seam for quilting. BUT!!! I was also told to use a 1/2" seam for the backing. I don't understand why. One person told me it was to make it stronger. This doesn't make sense to me. When I weld/bolt/rivet 2 metals together, only the joint and the material under tension is considered for strength, not the overhang.

    For example, consider a rope (quilt square) is tied to a tree limb (sewing machine thread). The excess rope (1/4 or 1/2 inch seam) from the knot is just dangling. On the other side of the knot is a length of rope I am hanging on(quilting square). Under no way does the dangling length of rope (the 1/4 or 1/2 inch seam) feel any of my weight. In fact, the length of rope (quilting square) and the tree limb (sewing machine thread) carry the full load. So how does the length of the seam matter at all?

    Please go easy on me-I am new, but also have a BS in Mechanical Engineering. But I am also asking the question from all of you who have forgotten more than I will ever know.

  2. #2
    Missouri Star

    Join Date
    Nov 2013
    Location
    Alberta, Canada
    Posts
    2,817
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    I think quilting is best done with 1/4" because that's the industry standard and patterns are all designed with that understanding. What you do for backing and attaching backing is really up to opinions I think. Probably someone once used 1/4" seam to piece their backing and they somehow ended up with a seam giving way and so that person told 15 friends that 1/4" wasn't enough of a seam low enough and it should be increased to at least 1/2"....but somewhere along the way the rest of the details of the story disappeared (perhaps the original quilter's tension was way off on her machine for that quilt, or it was a long time ago and the fabric used for the backing was already too old and thin and gave way in that area,,..who knows?)

    Like all other industry standards out there, they started somewhere for some reason...lol

    The quilt police won't mind if you do it your way, as long as you are having fun

    Terri

  3. #3
    Prairie Pointer

    Join Date
    Jun 2015
    Location
    Carrollton, TX
    Posts
    54
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    Well, let's say you are cold and pulling your quilt up toward your face. Your vertical stitches carry minimal load. The horizontal stitches carry most of the load as does your fabric squares and backing. The load is not equally shared between the 2 layers. The top has a much greater chance of failure. Think of a short chain vs. a long chain. Which would you rather hang from? I'll bet it's a short one. This mean the backing should be stronger than the top-assuming the fabric material is close enough to equal.

    OK, too many free-body diagrams. My point drifts aimlessly toward the fact that a 1/2" vs. 1/4" may mean the difference in needing more fabric.

    I really like you explanation though.

  4. #4
    Missouri Star

    Join Date
    Oct 2012
    Location
    San Antonio, TX
    Posts
    3,628
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    The extra seam allowance is stronger. If you pull that piece of rope, the one with 1/4" will give out quicker than the 1/2" one. Same thing with fabric. .... if you pull on the seams, the bigger seam allowance will hold longer because there are more threads behind the seam.

    Hope that makes sense.

  5. #5
    Missouri Star

    Join Date
    May 2013
    Location
    Orlando
    Posts
    5,978
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    I thought it was to be consistent with pattern writers. If everyone sews a different seam, then the size of their cut material would change. If each pattern writer creates a pattern with a different seam amount, there would be much confusion out there in quilting world. I am sure it had something to do with the strands not coming apart as well.

    I work for engineers, but I am truly not an engineer. And I hate doing math.
    Karen
    Life is short - live it up while you can

  6. #6
    Missouri Star

    Join Date
    Jul 2012
    Location
    Kauai
    Posts
    22,024
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    I have no clue but I just love your post!



    Lorie

  7. #7
    Prairie Pointer

    Join Date
    Jun 2015
    Location
    Carrollton, TX
    Posts
    54
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    Quote Originally Posted by snippet View Post
    The extra seam allowance is stronger. If you pull that piece of rope, the one with 1/4" will give out quicker than the 1/2" one. Same thing with fabric. .... if you pull on the seams, the bigger seam allowance will hold longer because there are more threads behind the seam.

    Hope that makes sense.
    It kinda makes sense. Considering the yield strength of fabric is much much lower than that of the thread.

    [[/I]

    Quote Originally Posted by Kgrammiecaz View Post
    I thought it was to be consistent with pattern writers. If everyone sews a different seam, then the size of their cut material would change. If each pattern writer creates a pattern with a different seam amount, there would be much confusion out there in quilting world. I am sure it had something to do with the strands not coming apart as well.

    I work for engineers, but I am truly not an engineer. And I hate doing math.
    I LOVE math.

  8. #8
    Prairie Pointer

    Join Date
    Jun 2015
    Location
    Carrollton, TX
    Posts
    54
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    Quote Originally Posted by Hulamoon View Post
    I have no clue but I just love your post!
    From a guy trying to analyze everything perspective

  9. #9
    Missouri Star

    Join Date
    Jun 2013
    Location
    grafton,ma
    Posts
    7,049
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    If you love math can we come to you with our math problems?(those of us that are not good at math)
    Joan

  10. #10
    Missouri Star

    Join Date
    Apr 2010
    Location
    Orange County, CA and Baarn, Netherlands temporarily
    Posts
    9,685
    Post Thanks / Like

    Default Re: Understanding seam allowance-from a mechanical engineering perspective (new guy)

    That makes no sense to me. Quarter inch seams on piecework hold up for many years. Quarter inch seams on the back of a quilt will last just as long, in my opinion. If you think it's going to benefit you in some way, then by all means sew 1/2" seams to join your backing pieces. After all, that extra 1/4" is easy enough to handle, right? Personally, this is the first time in all my years of quilting that I've heard this one. If it's a quilt that is only going to be tied and doesn't have the support of top quilting then maybe it makes sense. Who knows, maybe my next quilt will have half inch seams in it's backing? I know I'll most likely think about this thread next time I'm piecing a backing. hahaha
    Last edited by rebeccas-sewing; July 7th, 2015 at 03:23 AM.
    Goodbye Europe! Hello California! Home sweet home.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •