Tell me if this sounds familiar: You are slugging it out on a mill job in tough material that requires lots of metal removal, things are going poorly and you’ve got a whole pallet full of parts to run. After your first part, you run the numbers in your head and things are looking bleak when in walks a tool salesman that has got the perfect tool for your job. This tool can run 500 surface feet per minute with a .008” full width chip load .500” deep. Sounds too good to be true but the salesman guarantees the tool to work or you don’t have to buy the tool. You load up the tool, input his numbers into your program, change the work offsets for the tool and hit the go button. The tool enters the cut and all of a sudden your mill sounds like a diesel locomotive going 90 miles an hour. Chips are hitting the mill guard like machine gun bullets. The tool hasn’t completed two inches of cut when you begin to breathe a subconscious sigh of relief. Your hourly rate just doubled.
Somewhere further into the cut, unseen to the human eye, a microscopic corner of an insert breaks, then another larger piece of an insert breaks, the laws of physics begin to take over, and faster than you can say “tie me kangaroo down sport”, your diesel locomotive just threw about 9 rods. Five minutes later the adrenalin is still coursing thru your veins.
What caused the problem? Weak set-up? Wrong insert? Overzealous salesman? Who knows, it could be any number of things. We should always strive to get the most of our equipment, tooling and set up when it comes to metal removal, however, there are always trade offs that need to be considered when running a job.
Cutting tools have an amazingly short life span when you consider how much time the tool is actually in the cut. Therefore, to insure the maximum cubic inches of metal removal before regrinding a high speed steel tool or replacing inserts, we should do everything we can during setup that will allow us to take maximum depth of cut and use the highest feed rate recommended for the cutting tool without destroying the part or the cutting tool. Think about it, if you have the proper tooling and a good solid setup on an excellent machine, why run a tool at .003” feed per tooth when the tool is capable of a feed rate of .006” per tooth? The tool doesn’t care, it will be “in the cut” for just about the same amount of time in both situations before it needs to be reground or replaced. The second scenario however, will remove twice the material as the first. This same story goes for depth of cut.
I am not recommending that you use brute force on each job that comes through your shop. Every job is different and requires its own plan of attack. For example: If you are running just a few delicate small parts that have numerous setups, metal removal is not that big of an issue. On the other hand if you have a pallet full of large parts with lots of roughing work, you definitely want to think about running your machine like a diesel locomotive. What it comes down to is tooling, spindle speed, horse power, how well do you have a hold of the part and how rigid is your machine.
While this method is not gospel, it has served me well over the years and I hope it helps.
