Be sure to use sharp tools, a light touch, and have plenty of glue handy for stabilizing. Also, the larger the core (the soft, pithy part), the sooner you'll run out of cob when turning. If your tube is off-center by much, you can end up loosing the pattern. Good source of cobs is the pet area at Walmart - they have bird/squirrel food - a whole bag of dried corn on the cob - under $4 a bag - just pop the kernels off.
Be sure to post your creation!
Good luck