Based on A.R. design at http://www.thingiverse.com/thing:415761 but completely redrawn from scratch. This bobbin is designed to be printed as one piece horizontally. This is due to weaknesses inherent to printing cylinders vertically. For me, the other one stretched and broke the spool while winding. Since this is printed horizontally instead of vertically, the weakness on the spool is no longer present. This spool is also 2mm shorter than A.R.'s design to allow for stretching so that it still fits in the core. I have included a file with supports.

If you're really loading it completely, I would recommend a carbon fiber filament.

Order it printed by Shapeways at http://shpws.me/Me49

Use with ferrite core UY1658:
http://www.aliexpress.com/item/large-watt-U-shape-transformer-ferrite-core-UY1660-machines-equipments-10pairs-lot/493680068.html

Edit 2016/01/13
Added new stl for a bobbin with thicker center.

Printed in PLA at 215C, horizontally.