Support FreeCADs Material System

[jbaehr]

Right now BTL comes with its own material list. However, since FreeCAD/FreeCAD#14460 we have a material model providing the parameters required for the cutting force calculations.
With FreeCAD/FreeCAD#15910 and FreeCAD/FreeCAD#16021 I provided some data for various metals and woods. In the PRs you'll also find some example code on how to use the values (the one in the Wood PR is more advanced). I think it allows a better cutting force estimation as it takes the chip thickness into account: Removing two small chips takes more power than removing a single larger one; or the other way round: Removing chips of half the thickness takes more than half of the power. In addition, the cutting force changes with the tool's rake angle (and to a limited degree with the helical angle as well). From what I saw you just multiply the matarial-removal-rate with a constant (per material) factor.
The sample code also uses FreeCAD's Quantities for the calculations (instead of plain floats) and thus removes the need for various constants resulting from the differences in units -- The quantities take care of that which results in cleaner code.

I think your material system has the advantage of providing different surface speeds for different operations, though. here I summaries the current limitations in FreeCAD's. There are some ideas how to address them in FreeCAD/FreeCAD#16801 but we haven't come to a satisfying solution yet. Maybe you want to join this discussion as well?

[knipknap]

Thanks for the heads up! Definitely agree that the new material system should be used, I really like the approach and think it will make many things easier for users in the future.

I think it allows a better cutting force estimation as it takes the chip thickness into account: Removing two small chips takes more power than removing a single larger one; or the other way round

BTL already tries to account for the required power depending on the number flutes. While the operation-specific chipload calculations (in https://github.com/knipknap/better-tool-library/blob/main/btl/feeds/operation.py) are independent from the number of flutes of the tool, the feed is later adjusted, taking power requirements into account. The power requirement is calculated here:

better-tool-library/btl/feeds/calc.py

Line 197 in 7c27cc6

self.feed.v = self.adjusted_chipload.v*self.endmill.shape.get_flutes()*self.rpm.v

The number of flutes is just a factor, so this is linear for now. This could be further improved by adding in a) a non-linear curve for the "power required per flute", and b) a non-linear torque curve for the spindle (see #53).

From my understanding, a) would address the point you raised.