Sadly, this is very common.
We intend to print a nice part, but it ends up looking like spaghetti!
What happens is, if the bottom of the part slips from the position on the platform, the printing on top will just print into open space, and string along the plastic like spaghetti.
Every mistake is an opportunity to learn, and we're doing lots of this mistake+learn here with the MakerBot.
What we've found works well to avoid this spaghetti is:
- Ensure the platform is level & close to the tips. Calibrated the platform every day, and do it hot (as cold/hot have different positions, & it prints hot, so you must calibrate hot)
- Once the platform is close, then, use ABS+acetone in a slurry, and apply a little of this to the platform to create a more adhesive bonding layer to prevent new parts from moving while printing
- Print a "raft" or other wider bottom material in your design, so that it has a wider base, which is inherently much more stable to prevent motion later in the print