Offset trajectory path issue with circular Lead In/Out

[CVH]

Can anyone please explain the start and end cutter trajectory paths? The 'donkey ears'.
Example of basic offset post GCodeOffsetMM.

• Blueish is a traverse at Zsave.

• Dashed is the cutter trajectory at Zcut.

• Continuously is the contoured edge at Zcut.

The arcs in continuous Linetype are the intended Lead In/Out: An eighth circle with radius 8 ...
... I already have a problem with why this can't be with a radius less than the cutter diameter but whatever.

Donkey ears 1.png (2.83 KiB) Viewed 200 times

If we add representations of the cutter with R6 at various places then the milled contour itself is fine:

Donkey ears 2.png (3.35 KiB) Viewed 200 times

But if we look at that in detail for the start and end of the trajectory then things don't add up.

Donkey ears 3.png (7.38 KiB) Viewed 200 times

Instead of the intended cutter entry (green) I get a different arc entry shape (yellow) with a diameter of 21.68695112.
Then I figured that this is merely a representation where the cutter trajectory is somehow linked ... Connected to the edge being cut.

But looking at the G-Code it is exactly the dashed trajectory that is exported.
... G0 X-7.6569 Y22.3431 ... End of traverse at Zsave
... G1 Z-4 F150 ... Plunge to cutting depth
... G2 X-2 Y23 I5.6569 J-24.0301 F1000 ... Arc to (-2, 23) with radius sqrt(5.6569^2 + 24.0301^2) - R3 = 21.68696465

So, instead of a convex attack motion for 45° with R8 the real motion of the mill edge is concave for just over 13°with about 2.7 times the radius.

= = = = = =

Agreed, this is a corner case ... Let's force the start position to elsewhere:
It should be clear that the cutter ruins the face to mill on entry and exit

Donkey ears 4.png (4.02 KiB) Viewed 200 times

= = = = = =

IMHO connecting the cutter trajectory and edge being cut is wrong ... A mill cannot change in diameter unless it is conical.
... I would expect an offset to the edges with a fixed radius for a straight cutter, including the Lead In/Out or an offset to that:

Proper Lead In/Out at corner

Corner offset eighth circle.png (2.96 KiB) Viewed 200 times

Proper Lead In/Out at face

Face offset eighth circle.png (3.48 KiB) Viewed 200 times

Very similar to an offset path with 'Extension' type Lead In/Out where the cutter trajectory and edge are NOT connected at all.
But that may include a sudden engagement with the stock material where a circular entry can be gradual.

Proper Lead In/Out at corner

Corner offset extension.png (2.28 KiB) Viewed 197 times

Regards,
CVH