Originally Posted by shortgrass
Those that rely on CNC in place of skilled people and strict inspection procedures are kidding themselves. As for CNC, "garbage in = garbage out"! They are not infallible. The days of the manual tool and cutter grinder are not gone! That's where 'alterations' take place.
Next door to me was a tool and cutter grind shop. I probably had them grind 250 reamers a year in all sorts of oddballs shapes and sizes. They had the good old Cinn tool grinders (about a dozen of them), and right accross the aisle were a Walter and a Starr grinders. About the only thing they did on the old machines was odd shaped end mills and a few step drills that were one up deal we were experimenting with. A completely rebuilt Cinn will not grind any closer than a Starr, and when dealing with multi steps with several radiuses the Starr was far better. Now if I wanted to get a reamer that was well less than a tenth in runout I ran it accross a Studer, and then hit the reliefe on a Cinn tool grinder (the Studer will not cut the reliefe and back off very well). I've seen reamers come off a Studer that had less than .000075" error a lot of the time. But that process is slow, and takes an act of congress just to get into one of those machines.
Cutter grinding be gone? I hope not! We had several large grinders just for sharpening broaches alone. A Red Ring and a Magg gear grinders for doing nothing but shave cutters (these are ground as accurate if not more accurately than any reamer). A half dozen or more drill grinders that were always in a back log (we ground a lot of multi step drills). And a pair of custom built web grinders to redo the web on drills (I built them). Plus two grinders for nothing but gun drills. These were kept covered up unless thyey were using them as the processes were very secretive. There was even a couple of lapping machines to take another half tenth off a reamer when needed. But the inovation of the indexable insert certainly has taken it's toll on cutter grinding, and the TIN coating processes have greatly increased cutter life. I hate to think about how many tons of cutters we sent out for replating a year!