Need Help Creating 3D Images

[kdub]

I make 3D images a lot and have been doing it for years, 99% of the time I start with a jpeg, then create a new platform using a transparent background, copy the image on to that, use the object magic eraser tool to make the background disappear, then save as a gif, seems to work good.
But my question is how can you get it cleaned up around the edges so I can place this on color pages instead of white?

Example:
start with jpg


Next transparent B/G


Transfer to color B/G




Thanks
Ken