[HuFlungDung]

Chris,

You've nailed one of the difficult areas of machining. Not only does this problem apply to cnc but to many types of manual machining as well.

If you want to cut right through, you would definitely need a sacrificial spacer. MDF is a pretty decent product so far as being quite flat and parallel sided. And, its cheap. So this makes a good spacer material.

Care needs to be taken that any cutouts do not get completely cut loose with the cutter still in the cut. This may force you to plan a method to hold the scrap area, by, for example, drilling a hole (or holes) through the workpiece to fasten down the loose cutouts. Or, you can turn such areas completely into chips, too.

I think you could find some texts used in machine shop courses in some technical schools. If you have no metalworking experience, a course outlining the methods used in manual machine operation would make a sound foundation for you to work from. CNC machining practice is based on manual machining methods. The computers involved permit you to undertake difficult toolpaths and to attain repetitive part consistency. But, cnc is no magic bullet so far as the basic principles of workholding, feeds and speeds, material machining characteristics, tool types, etc.