Metal Casting Project Failure

This past weekend while I was camping, I fired up the flower pot furnace that I constructed for the first time.  Needless to say I did not have success.  First, I put some hot coals from the camp fire in, turned on the air intake fan and closed up the lid with an aluminum can place inside the furnace.  Nothing happened in 12 minutes and it didn't seem to be very hot.  At this point I added several charcoal briquettes.  After about 24 minutes there was still no melting but the outside of the furnace was starting to get hot.  After 48 minutes there was still no melting, so I opened up the furnace and added more charcoal and left it open until all the charcoal was lit.  Then I closed it up.  After about 2 hours there was still no melting, but the outside of the oven was quite hot.  Looking at the charcoal, inside it did not look much hotter than what you would see in a grill.  The speculation is that the small fan that I used was not providing nearly enough airflow to get the charcoal hot enough.  The fan that I used was a small 12 V CPU fan.  As I recall the flower pot furnace pamphlet recommended using a hair dryer fan.  I will retry again with a bigger fan as soon as possible.

Here are some pictures of the furnace.