Check out the "Sew Easy!" Group here at Thingiverse. It is all about sewing supplies, 3D printed fashion and tools related to threads and fabric http://www.thingiverse.com/groups/sew-easy"
This is a quick design for a customizable sewing guide that uses two magnets embedded into the guide for holding it in place on your sewing machine.
It can be used with cylinder and rectangle magnets of adjustable sizes. The size of the guide can be adjusted as well.
I did not add code for checking correct sizing boundaries, so choose your values correctly ;) and check your design before using it.
New in this version: I have added the possibility to print testpieces, this helps in testing if your magnets fit into the holes of hte guide. The testpieces are just big enough to cover one magnet, so they are fast to print for rapid testing.
The sizes for the default magnets fit a 5mm cube magnet and a 5mm radius cylinder magnet with 5mm height and the sizes are adjusted to fit my printer setup with a 0.4mm nozzle.
Used the simple Cura Settings: 0.4mm Nozzle, PLA, Normal Quality
Either glue the magnets into place or press them into the holes and attach the guide to your sewing machine.