This is a DNA model that i have created which is meant for display on a desk or some sort of display'ish area. I have printed this design on the MakerBot Replicator 2 with no supports or rafting and it worked perfectly. This design will not need any supports or rafting because the printer (at least the MakerBot) can stretch a piece of plastic over an area multiple times to create the cross sections, and the double helix is greater than 45 degrees making it easily printable. I do recommend decreasing the hollow area on the inside (making the object more solid) to improve the strength. Should be able to print on any scale, but the smaller the easier the printer can print the cross sections.
The last Photo is a modification of the the given file (IS NOT THE FILE THAT IS GIVEN) that was designed for a friend. That is only photo i have of printed version, but as you can see the cross supports came out fine with no supports.
NO SUPPORTS NEEDED. No rafting needed. Recommend not increasing the scale, if anything, decrease it.