[SOLVED] Offset trajectory path issue with circular Lead In/Out
Posted: Sat Mar 23, 2024 7:21 am
# EDIT # Solved, considered as a bug, see lower.
https://www.qcad.org/rsforum/viewtopic. ... 206#p45292
Can anyone please explain the start and end cutter trajectory paths? The 'donkey ears'.
Example of basic offset post GCodeOffsetMM.
... I already have a problem with why this can't be with a radius less than the cutter diameter but whatever.
If we add representations of the cutter with R6 at various places then the milled contour itself is fine:
But if we look at that in detail for the start and end of the trajectory then things don't add up.
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
= = = = = =
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:
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.
Regards,
CVH
https://www.qcad.org/rsforum/viewtopic. ... 206#p45292
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.
... 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 60603 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 60603 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 60603 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 60603 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 60603 times
- Proper Lead In/Out at face
- Face offset eighth circle.png (3.48 KiB) Viewed 60603 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 60600 times
Regards,
CVH