If you're not familiar with the term "truing", don't be alarmed. In a nutshell, it basically just means making sure all your seams and darts are properly aligned so that when you assemble your garments, you don't have any odd jagged connections between pieces.
Truing adjoining pattern pieces
Let's take the example of a darted bodice pattern piece that you've just drafted or adjusted. You might check the following:
- Place the front and back bodice pieces together at the shoulders and check that the armscye curve is smooth and the join at the shoulders doesn't have any sharp angles or kinks.
- Place the front and back bodice pieces together and check that the shoulder seam aligns and that the back neckline curve is smooth without any sharp angles or kinks at the connecting point at the shoulder. Note that because of the back shoulder dart, the shoulder length will not be equal between the front and back pieces, so you shouldn't expect them to align at the same time - check from the neckline end of the shoulder seam up to the dart leg on that side (the highlighted part of the shoulder seam), and then from the armscye end up to the other dart leg.
- Place the front and back pieces together at the underarm point and check that the armscye curve is smooth and has a nice smooth connection at the underarm (the pink curved arrow). On this pattern, there is a notch on the back piece which should align with the side dart on the front piece when shown, so I would check that that notch is in the right place (the highlighted section of the side seam).
- Check that the side seam length, below the side dart is the same on the front and back pieces.
- Fold out the side dart and check that the side seam lengths match (although you've effectively checked this by checking both parts of the side seam in the previous steps). You can also lay the front over the back, right sides together, with the dart still folded out, and check that the curves/shapes of the side seam are the same. That will make it easier to sew them together. If they aren't, just trace off the back's side seam shape onto the front and trim the front accordingly.
Truing joins between seams
So, what do we do if any of these connecting points are sharp, rather than smooth?
If you have two adjoining pattern pieces with a 'peak' in their connecting line, just redraw the join to smoothen out the peak. In the image below, the original blue line indicates a join where the lower edge of the fabric is not even. Assuming this is intended to be a straight edge, you could redraw it as shown in red. The angle between the red lines, at the base, should be 90 degrees.
Similarly, looking at the blue lines in the image below, we have a curved seam which is not intended to meet in a peak or dip, which crosses a vertical seam. Perhaps it's the base of the armscye, meeting the side seam. We can straighten out the curves for approx 1/2" (1.2cm) on either side of the vertical seam, as shown in red. Again, they should meet the vertical seam at right angles.
Lastly, if you have a mismatch between the edges of two adjoining pattern pieces, just draw a new connecting line which splits the difference between the two. In the image below, the red curve takes a little width off the top pattern piece and adds a little width to the lower pattern piece. As mentioned above, you will often see this kind of mismatch in seam length between front and back shoulders, where the back shoulder piece includes a dart or extra length intended to be eased to match the front. In those circumstances, you wouldn't make the adjustment below.
Truing dart bulk
Let's assume you have just drafted the pattern below, with a side dart as shown.
Before you add seam allowance, you'll want to true the dart bulk as follows.
- Fold along the central line of the dart, and then fold the dart in the direction that it will be sewn when making the garment. As this is a side dart, we'll true it with the dart folded downwards, so fold the dart down and tape it in that position.
- Draw the desired side seam over the folded dart, in this case a straight seam from underarm to waist as shown in red below.
- Using a serrated tracing wheel, trace over the seam edge, through all thicknesses of the paper.
- Open out the dart (by cutting through the tape if it does not lift easily), and trace over the dotted lines to draw in the shape of the seam at the dart bulk.
- As you can see, when this dart is folded down, it lies flush with the side seam. If you were to fold the dart upwards when sewing, you'd see that it pokes out from the side seam.
(Correctly trued - "right side" view)
(Correctly trued - "wrong side" view)
(Dart folded in opposite direction - does not align with seam)
So next time you're sewing up a dart, if you have any weird 'tails' like the one above, try folding the dart in the opposite direction in case that's the direction the dart was actually trued for.
And that's pretty much it, a basic introduction to truing!