I got asked the other day, how to alter the Tippi pattern into a boy pant, so I thought I'd stick a tutorial up on how I would go about it. I have left all my workings out on one piece so you can see and compare how they sit from one piece to the other.
The light blue is the Tippi pattern, the dark blue with the yellow stripes is the new pattern.
The red lines are your anchor lines and the pink are your shifting lines.
Front pattern piece of Tippi
Draw around the pattern piece, all the patterns that are available on this website have a separate gusset piece, this makes altering the pattern piece easier as you don't have to worry about re-shaping the gusset piece back in.
Basically if you have a brief shape you're happy with and want to alter it to a boy pant brief I start with the following .
1. Lower the waist - boy pants should sit lower and more on the hips, depending on the style I would lower by 1cm. (pink guide line 1cm, shift the pattern down and draw in the new waist line)
2. The depth of the side seam needs to deeper so on this pattern I have deepened the side seam by 4cm. Also as the brief is sitting more on the hips then your legs have to be wider, as the briefs won't be sitting on the natural crease of the leg, but will be sat across your hips. Usually the legs are also seam covered or if elastic is attached there won't be as much tension on the elastic as the previous briefs (the tippi ones).
(pink guide line 4cm, shift the pattern down, also shift edge of pattern to the red vertical guide line of 2cm and draw in bottom of side seam and legs corner.
3. Connect top of side seam to bottom of seam seam using a ruler.
5. Draw in new leg shape, blending into the gusset area (approx 2cm up from the bottom), the curve of the leg can be done either with a french curve or the brief pattern.
Remember the new leg curve has to come up and then go down to the side seam, rather than just curving into the side seam, this allows for ease and movement of the legs. (if you're unsure if you have done this correct, get a set square and from the vertical guide line, square off into the bottom of the side seam, and you should see that part of new leg line is above the horizontal line (set square).
Back Pattern piece of Tippi
The back brief measurements are the same increase as the front.
1. However to start with, re-join the back brief pieces (the Tippi brief is in two parts, to allow two fabrics to be used). It's easier to re-join your pieces at the start, knowing that they work and cut them up afterwards re-adding the seam allowance.
2. I drew 1.2cm on the top piece so the pieces would re-sit flush again (pink dotted line: 6mm seam allowance plus 6mm seam allowance).
3. Follow the same order as the front pattern piece (waist, side seam and legs). This time with the legs you're making the new line (once it's blending into the gusset seam and side seam), as straight as possible with a slight curve outwards. This is because with a boy pant it covers the butt cheeks more, than a bikini style brief. and doesn't have to sit flush against the skin.
4. For the window part of the brief (lower part) I extended the seam curve line out (blue dotted line), this pattern was then cut along this blue line, and 1.2cm was added along the line (the seam allowance as you chopped it off previously).
Remember to make a toile and adjust accordingly, but this is a good starting point for your boy pant.