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Linear vs curved feeds and speeds


Using the harveytool website I learned how to do F&S for thread mills given desired SFM and chipload for a specific material plus the number of flutes.  The result is a linear speed, and I should get similar results in GW by entering these three items plus the tool diameter.

However, for thread milling the linear speed has to be adjusted.  For external threads the feedrate needs to be higher since the tool’s center is moving over a larger arc than the cutting edge.  For internal threads the adjusted speed is lower since the path is shorter.

So it occurred to me that if I rely on GW for feeds for spiral hole milling that it might be too fast?

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Best Answer

The Interpolate Mini-Calc does these sorts of adjustments for curved feeds and speeds.  Unless the curve is small relative to the cutter, there typically isn’t too much adjustment needed.  The cutter makers know you’ll be plowing into corners and going around curves, so they quote numbers such that linear feeds and speeds are good enough.  Where it can come into play is when precision is essential.  Thread milling and trying to make an interpolated bore as precise as possible are good examples where it can help.

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