On 12/5/2015 1:29 PM, (PeteCresswell) wrote:
Per Muggles:
Well, it's base material is spandex, but some swim suit material can be
a combination of fabrics.

It sounds like you have some significant sewing/materials expertise.

Here's a question: I just finished sewing up the second trampoline for
my little outrigger canoe/trimaran
(https://picasaweb.google.com/1081497...08896384953378)
using material from the backyard trampoline that a neighbor put out for
the trash collectors.

I'll draw a perfectly straight line on this stuff, then I'll cut that
perfectly-straight line, then I'll fold a hem, iron a crease into it and
baste it using basting tape, then I will check again that it is
perfectly straight... then I will sew it and it will come out slightly
curved.

Any idea on what's going on there? I am thinking it has to be
something about the way the machine's foot compresses the weave a little
as it moves along and there's no way around it....

Your stitches aren't following a single thread-line in the fabric.
I.e., the fabric can be thought of as a grid. But, your stitching
isn't perfectly *aligned* with that grid. So, the structure in the
fabric (i.e., which "horizontal" threads you're crossing along with
which "vertical" threads you're crossing) biases the stitch you're
making.

You also need to ensure top and bottom thread tensions are balanced.

A zig-zag stitch is usually more "accommodating" than a straight
line stitch; it has some elasticity in its structure. (and, moves
each penetration of the fabric farther apart for a given amount
of "forward motion"; sort of like walking/wobbling with legs wide
vs. taking baby steps to make the same forward motion)

Or am I just wishing it was still straight before sewing ?

Not a huge deal... but inquiring minds want to know....