Some of the face normals are facing to the inside of the object rather than all face normals facing to the outside of the object. [Read below for an excruciatingly detailed explanation of face normal.]
You can see incorrectly facing face normals after the object is Edit>Aligned to 0,0,0. After this operation, most areas of the object are not red [which they should be when highlighted] but are a dark green on my monitor [they could be black on yours].
If the object is rotated so the underside is visible, most of the underside is red and other portions are dark. Again, the faces being red means that is the face normal, which indicates that face normal is facing the opposite way of how it should be so a toolpath can be generated.
You need to get all the face normals facing out so Cam Bam can see them. As they are Cam Bam thinks that surface does not exist when seen from the orientation you need to generate toolpaths on what is termed "the top". And Cam Bam is doing is job correctly, the STL has just given Cam Bam the wrong information for it to function as you expected. Probably those digital demons fussing on your computer ....
There should be a operation in the Edit function on the tool bar of your CAD software to make the normals all face one way.
ALSO SEE: http://www.cambam.co.uk/forum/index.php?topic=1989.msg11641#msg11641
This is from CNC Zone:
The orientation of the surface normals of the object are opposite of what they should be, which is why Cam Bam is machining the back; its doing exactly what it is suppose to. I know this VERY well as it was one of the processes in CAD that can really drive you mad in CAM.
Read this to get a good grasp on "normals": http://csanet.org/newsletter/winter01/nlw0107.html
REMEMBER THIS: When an object is Selected in Cam Bam, it turns red.
So do the following to solve your dilemma:
1. In your CAD program, reorient the normals to the top of the object [the convex surface].
2. In Cam Bam, Edit> Align Objects and enter these settings: X to Left with a zero value [0 in the white box at the bottom of each axes column]; Y to Bottom, with a zero value; Z to Upper with a zero value. This will align the object along the X and Y axes, and will make the surface of the object the Stock Surface.
1. Use the Advanced settings in the Object Property Window [the one on the bottom on the left] to enter the parameters of the Tool Path.
See User Interface in the Help screen.
2. Set Boundary Method to Shape Outline [the default]
3. Set Boundry Margin to -0.15. That will keep the cutter on the surface and so it does not try to cut the edges.
Read this for a full explanation by Andy, the inventor of Cam Bam. Inefficient and unexpected moves during machining 3D profile http://www.cambam.co.uk/forum/index.php?topic=2013.0
And finally, I am not a genius, I made everyone of these mistakes, and more than once too!!
One last suggestion: Go to the Cam Bam Forum and search STL and 3D. That is how I began solving my problems when I switched from 2D/2.5D to 3D.
Give this a go and if you still have problems, post again.