Great question! I too would like to see the answers. Thanks for asking.

Go to YouTube and type in double needle sewing. There are sew many videos on how to do it, getting over your fear, and ideas on how to use.
Love the YouTube I learn so much

Ask the emblibrary team at http://www.emblibrary.com/EL/default.aspx

I have used double needles a few times. They aren't really difficult to use, just remember to slow down the speed of your machine or the thread may break frequently.

I have used the twin/triple needles - mostly for dish towel - an extra border with two different thread that match the design.

I used to be a big ol' chicken about twin needles and then they were shown in some sort of class I took for my new machine. They are wonderful and make your sewing look like you have just slaved for days. I now use twin needles when I revamp the sleeves and necklines of my T shirts. When I shorten my hubby's T shirts I use the twin needle. Really cool with two diff colors of thread and of course the two lines of stitching are perfect. Very important that they fit your foot. Some are too wide and would hit the side of your foot. I used to know how to figure and measure but I have forgotten. You could always install you needle and then use your wheel very slowly, by hand. Go ahead and have fun with these needles, they are also great for sewn down hem on childrens clothing and I do my summer dresses and swim cover ups with the twin needles. Sharon

Thanks for asking. I'm interested too * :o)

Whenever I've used twin needles, the bobbin thread seems to pull the fabric together. Does anyone know how to fix this problem?

I believe that Saproctor used a Wing Needle not Twin needles in her projects.
Perhaps check her projects again.

You would have to check in your machine manual for the size of Wing needles your machine would take as some can use 2 different sizes and some only one and others can't used them at all.

EastWitch2

You might have to play a bit with the upper tension, depending of the effect you want to achieve, either small "ridges" or flat parrallel fancy stitches (you can use two colours for those). Have a look in your machine manual, it should tell you how to thread the machine and maybe say something about the tension as well.

I often use a wide twin needle (6 mm) to hem sleeves and lower edge of stretch T-shirts.

Just came across this post. Yes I did use a twin needle on two of the doileys. Use your satin stitch foot. I used a 80/2.0mm needle width 5mm and length 0.35 When threading separate the threads at just above the needle. Just play around with stitches and widths making sure that both needles will not hit the foot.
When I used the twin needle on the sewing caddy I had a cord under the fabric to give a more raised effect using a pintuck or cording foot. This was only on the straight rows. Hope this helps. Shirley

Thanks for asking this - interesting!

Great question!