Originally Posted by mstone
Producing a chassis involves a little more than just milling. The original rough cutting of the stock, perhaps two or three mountings in the CNC, several QC steps, polishing, machine clean up between runs, and there may also be a few defects thus the 8 per day per machine may actually be realistic. Furthermore you can't cut it too quickly otherwise you may end up with distortions from heat even though it is being cooled. The really tight tolerances and thin clearances require slower cutting.
While it's true that there's more than the milling involved in producing the chassis, most of the rest of what you say is not current for any production environment.
1. No production shop is going to require "2 or 3 mountings" to machine something this simple. Each section may have to be flipped once, which would be handled robotically by the machine. No manual resetting required.
2. Most cleanup of the machine is going to be done by the machine. Material is removed by conveyor or other means. Even tooling will be replaced automatically on modern production machines as the spindle load increases or it reaches it's hour-life. Occasionally the machine will have to be inspected and possibly cleaned/serviced manually, but this would be more like once a month.
3. QC would be done at different stages during the process, with most of it being done by machines as well. Surface finish, cracking, etc. can all be measured by machines better than by people. One part out of X many would be taken to manually inspect, but this wouldn't slow production. Anodizing and polishing would be the final steps. Some extra time would be eaten up here, but minutes not hours.
4. You'd be surprised how fast Aluminum can cut. It's not true that you "can't go too fast". Major heat buildup in aluminum comes when you cut too slow, not too fast. Modern machines are limited in their cutting speeds only by how fast you can physically move the cutter or table, and the required HP to sling that much metal.
5. The tolerances and "clearances" are not even remotely tight. For starters, really tight tolerances would require other machining methods than milling.