Trochoidal milling tool paths are all the rage. Light radial width of cut at full axial depth of cut. It works so well, let's make the endmills with longer and longer flute lengths.
Problem is the most flexible part of a tooling system (endmill, toolholder and spindle) are the flutes of the endmill. On a 1/2" 4 flute endmill, about 70% of the mass is removed to grind the flutes, so its stiffness is equivalent to a 0.350" rod. As the chart below shows, the a tool's performance degrades as the flute length increases.
It is as simple as this: The more flexible a tool is, the more it deflects on a tooth impact and the longer it takes for the next tooth get back to workpiece. That means you have to slow the spindle speed down to wait for that next tooth. To reduce the deflection you have to reduce the force. With trochoidal, you do that by reducing the radial width of cut and your metal removal rate suffers.
Too much of a good thing is sometimes too much.
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