Here is a tool that was tap-tested in a 10,000 RPM spindle. The fastest and deepest available lobe was just under the 10K limit. I intentionally expanded the range of the stability lobe diagram to 17,000 RPM (shown in green) so you can see the big dominant lobe at about 16K. It would cut 25% deeper than the one at 10K. BUT, I CAN'T ACCESS THAT SPEED with this machine.
If we LENGTHEN the tool the lobes would shift to the left and that large lobe, or one of the two other deeper ones, may become available under the 10K limit. We are making the tool more flexible in order to improve its performance. Its not that longer tools are more stable, per se, its that we are dealing with the constraint of available spindle speed.
Of course, other things may change, frequency-wise, if we lengthen the tool too much, but if you are able to measure it, you can dial in the tool for maximum performance.
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