Four tricks/tips -
- use a 'former' to control the stitching around the shape of the curve. ie. cut a template, (temporarily) stick it to the fabric and stitch exactly on the stitching line. If necessary, crank the machine by hand to ensure precision
and
- use a very short stitch length to stitch any section that requires trimming and/or clipping close to the stitching line. How short depends on the size of needle you're using, the thickness of the thread and the closeness of the weave of the fabric. A 1mm stitch length is a good place to start.
(Bear in mind that a size 90 needle needs a stitch length of 0.9 or more, or it's possible that the needle point will slip into the previously made hold and that can muck up the stitch formation.)
If you're using a thin thread rather than a sew-all, for example something like the thickness of a polyester 40s machine embroidery thread, it's worth stitching around the curve and notch twice, once on the line and the second pass in the seam allowance but snugged up to the first line of stitching. It's the same principle as the hairline seam technique. Also, tiny stitch lengths also means you don't add bulk with reversing or locking stitches at the start and end.
and
- grade and trim the seam allowance as close as possible to the stitching - eg. in the region of 1.5 and 2mm. A useful tip is to angle the scissors as you trim the seam allowance away in this section. When you trim this close to a seam, often you don't need to clip/notch around the curve.
and
- take care to be gentle when turning to the right side and use the former (aka template) to hold the shape of the curve for pressing. It helps a lot with achieving symmetry.
For neckstands and other curved shapes (eg. curved pockets) I often make formers from thin vinyl placemats (no seam allowance) which also makes them very useful as pressing aids.
Some general links -
http://curvysewingcollective.com/ten-tricks-for-sewing-better-collars/https://mavenpatterns.co.uk/how-to-make-patch-pockets-perfectly-every-time/