Football coaches have an expression during practices that is called "Best on Best". That is where the best offensive lineman is pitted in a drill against the best defensive lineman or the best wide receiver against the best defensive back.
This often isn't the case when tooling case studies are compiled. Often a carbide tool is replacing one made of high speed steel and the enormous performance gains are trumpeted. Rarely do you see a "Best on Best" comparison in our industry.
We do a lot of tests. Since some of our work is university or government related and must passed the rigorous scrutiny of peer reviews, we follow a strict "double blind" process. One engineer conducts collects data and assigns a random identification number. Since they often are in the field and may be influenced by those around them during the tests, the data is sent to our facility in State College where the analysis is done by a second engineer who is working with only the random identification number. Often what we discover is completely counter to our theories. This can be very frustrating.
But, some testing at some places is done with a desired result in mind. Results that are counter to that which is desired are thrown out.
The 400 meter dash is not really a dash. The runner accelerates to top speed in the first 100 meters and is able to maintain that pace through the next 100. Humans can't run flat out for much longer than that so the last half of the race is slower than the first. As they round the last turn they are more upright and straining to hold on. There is no such thing as a finishing kick. The winner is the one whose speed deteriorates the least. That's the 400.
What does this have to do with milling tools?
For each machining center there is ONE PERFECT TOOL. The right combination of toolholder, endmill of the right geometry and sticking out the right amount. It will run as fast and remove as much metal as that machine will allow. Any change to that tool, sticking the endmill out further, changing the length or type of toolholder, changing the endmill's number of teeth or its geometry will cause deterioration from that maximum performance. Unfortunately, tool catalog charts and CAM software don't tell you that. They give you one speed and feed recommendation regardless of the tool configuration.
You should try to find and use that ONE PERFECT TOOL as much as you can when programming parts, knowing that any changes you must make for reach or other concerns will result in a loss of performance, longer cycle times and higher costs.
Mike Tyson once said:
“Everyone has a plan, until they get punched in the mouth.”
The same could be said when discussing the runout of an endmill assembly. As soon as one tooth of that endmill makes contact with the workpiece, it will deflect the entire endmill and when it exits, the endmill will rebound past its original centerline. That prompts another quote, this time from Sir Isaac Newton:
“For every action, there is an equal and opposite reaction.”
In other words a toolholder’s touted “close to zero” runout doesn’t survive the first revolution of the endmill in a cut. Claims that improving runout alone will automatically improve tool life are misleading. If the spindle speed (and resulting tooth impact interval) is not in time with this back and forth, deflection and rebounding cycle, the tool is running out in the cut, not matter what it measures at rest. Of course, minimizing runout is a good practice to create a robust repeatable process, IF you know its dynamic behavior.