Laying out darts on paper patterns

[Steve Murphy]

If you follow Evan Wilcox on Instagram you will know he specializes in making aluminum petrol tanks for motorcycles.
He uses darts on his paper patterns where he need to get wrap around shapes. I noticed he tends to use concave darts, which have cut curved cut lines.
so, using google I found that there are a number of different type darts used in the sewing world depending on what shape you are trying to fit against.
The concave darts would be used for a errr, rounded shape or two.
I haven’t found a method to lay these out, other than by eye. is there a more scientific method?
thanks,
steve

[Jaymce]

In sewing they are marked when the pattern is assembled.
frame and foam are assembled
Thin cloth layed over and marked ie. Bottom seat.
Vertical sides of seat bottom are layed out and pinned to seat bottom.
witnesses marked made on fabric while assembled.
pattern disassembled and darts marked.
Pattern transferred to leather, vinyl, finishing fabric.
When sewing if darts are aligned shape will be maintained.

Could be used in patterns with metal using flexible shape pattern methods or paper pattern assembled over a shape you are trying to recreate using a sharpie.

I will put a few witness marks/ scribe lines across fitted panels prior to welding and cutting on a curved shape for the same reason (maintaining alignment of 2 curved parts).

[ojh]

The 'dart' in fabrics is required because they can't shrink or stretch like we can in metal shaping.

[Moving molecules .]

Pics please.... What is a Dart? For sewing....

[Jaymce]

Daets are the same as whiteness marks. Used for material alignment. In sewing they are usually small pyramid cuts made by folding the material over on itself and cutting at an angle. The black dotted line would be the stitch line (my machine is not threaded right now and is threaded with white). The darts would be on the inside of the seam so they would never be seen unless the cover was disassembled.

Once I have proper alignment of my panel in shaping I will scribe the cut line but also mark the panel with marks that are at 90 degrees +- to the scribe line on both panels. This allows you to maintain the same positioning once you begin welding and tacking.

I would usually scribe with a scribe or utility knife.