I've had enough of 'girls' band t-shirts. So this is what I did to make this men's set-in sleeve t-shirt into a rockin' baseball tee.
1) Lay the shirt down flat and inside out. Starting on the front of the tee, draw a mark on the collar about 3 cm from the shoulder seam.
2) From the underarm point draw a line that follows the existing seam for about 5 cm.
3) Continue from the underarm mark to the collar mark with a line that curves towards the shoulder slightly in the middle.
5) Try the tee on. If you're happy with the placement of the 'sleeves' then cut them out!
6) Fold a large piece of paper in half and then open. Place the section you removed from the t-shirt on the paper, aligning the shoulder seam with the folded line. The fold line will be the grain line of your new sleeve. Trace around the material and add seam allowance.Voila! A Raglan sleeve pattern.
Optional - Adding Width:
7) Your raglan sleeve will be as tight/loose as the original sleeve. If you are happy with the way the sleeve fitted, there's no need to change it. I needed to add more width to the bicep area.
To add ease draw a horizontal line joining the two underarm points. Make a cut up the grain line but leave a tiny bit to connect the two sides at the top (collar). Also cut along the horizontal line, again leaving a small section to connect both sides. Then, separate the inner corners of the cross.
As you can see in the photo above, I added a 2 cm square to the centre of my sleeve.
Slip more paper under the pattern piece and tape it down. Draw a straight line joining points A and B and cut. This is the new hem line.
8) Cut your new sleeve from your fabric (WASH IT FIRST! Especially if adding a coloured sleeve to a white tee, like I did). Sew the underarm to hem seam.
9) Align the sleeve underarm seam with the underarm seam on the t-shirt. To make sure there aren't going to be any nasty surprises pin the sleeve to the tee without stretching. Then sew the pieces together.
10) Baseball t-shirt collars are bound in the same fabric as the sleeves. So cut the rest of the old collar off your tee with the tops of the sleeves you added, then measure around the new neck hole. Cut a strip of fabric a few centimetres longer than this measurement and twice as wide as you want the collar to be (my strip was 4.5 cm wide by 55 cm long). Pin it around the neck, SLIGHTLY and EVENLY stretching as you go. Mark where the ends overlap then sew. Sew the neck band to the neck opening. You could use this method to finish the sleeve hems, but I left mine raw - I like the way that knits roll slightly.
Ta da! A totally tuff women's tee made from an awkwardly-shaped men's t-shirt. Yours will be better than mine, because mine is misaligned at the back and I didn't stretch my collar strip evenly, so the is some slight gathering at the back. Fortunately this knit is fairly forgiving and I don't think that either accident is hugely noticeable!
There are some great tips and tutorials for sewing knit fabric out there but I've found it so much easier to just bypass sewing and rely on four-thread serging to hold my t-shirts together.