The following tips and unusual methods of machining have worked for me and may assist you.

• When I saw some flimsy Delrin parts being run, I hoped I wouldn't have to get involved. The programmer chose to apply large endmills to machine the parts. Initially, the job was not going well. Parts were being pulled from the vise jaws, and chunks of Delrin were flying. So I asked to get involved. I reprogrammed the parts to be made with smaller-diameter endmills, which cut with less pressure. I also chose to use single-flute cutters with a 0° rake angle when necessary to avoid the lifting forces inherent with positive rake endmills.
  
• When verifying a program, set center drills to spot only. Let's face it: We're only human, and sometimes we screw up. When drilling a part, especially one that already has a lot of time invested in it, care must be taken that holes and other part features end up in their correct locations. One way to verify the setup when drilling is to set the center drill to just lightly spot the surface. If the locations happen to be off for some reason, you'll have a chance to correct the error.
  
• Manually set countersink depths at the machine. Countersinking tools run the gamut in terms of how they are made. They vary in numerous ways, such as angle, tool tip size and number of flutes. These variations make it difficult for a programmer sitting at a computer to set a precise depth. Because machinists generally set a precise depth for a countersink tool, a programmer likely won't know which countersink tool will be used. Instead, I program the tool tip to stay a little above the part and let the machinist manually find the correct Z negative value, which then can be entered into the canned cycle that runs the tool.
  
  The easiest way I've found to do this is to run the program until the countersink tool is called up. Then, stop the program by hitting the reset button. After that, start the spindle with the clockwise, or CW, button, and slowly handle-jog the tool to the proper depth in the part. Take note of the depth using the operator's digital readout. Enter that value in the canned cycle that runs the tool. The only catch is that the operator's screen must be zeroed in to Z beforehand to the tip of the countersink tool, or the value shown on the screen won't make sense. Dimensions for countersunk holes are generally not too critical. These dimensions are used mostly for flat-head screws and lead-ins for tapped holes.
  
• Be especially careful when running large parts with the machine's doors or windows open. Occasionally, you'll run into capacity issues with machines. These issues often can be overcome with thoughtful planning. Sometimes, you must leave a machine's doors or windows open to accommodate a part or feature of a part. Make a mental note to be extra-cautious when doing this. It's a recipe for crashing because your travel may be limited to the openings of the doors or windows, not the total travel of the machine table. I once saw a nasty crash when a machinist clamped a long plate to a machine table with one end of the plate hanging outside the doors. For whatever reason, the machinist homed the machine. In rapid mode, the table went home but not before leaving a big gash in a door as a result of the edge of the plate slamming into it.