- Status Closed
- Percent Complete
- Task Type Bug Report
- Category QCAD/CAM
-
Assigned To
Andrew - Operating System All
- Severity Low
- Priority Very Low
- Reported Version 3.29.0
- Due in Version Undecided
-
Due Date
Undecided
-
Votes
1
- CVH (18.07.2024)
- Private
Attached to Project: QCAD Bugtracker
Opened by Lorenzo - 13.07.2024
Last edited by Andrew - 27.08.2024
Opened by Lorenzo - 13.07.2024
Last edited by Andrew - 27.08.2024
FS#2585 - Tabs are missing move back to original height after tab in certain situations
Often CAM tabs end up being not complete: they include Z up to shallow depth but not necessarily always include the Z down to nominal cut depth. As a result Z stays at the tab’s shallow depth until the next complete and correct tab is met.
When tab are created it should be systematically checked that all tabs are complete with “up to shallow depth” and “down to full cut depth” commands.
tab_issue.png
NEWYD_MODEL_DECK_24cm.nc
Related Forum topic:
https://www.qcad.org/rsforum/viewtopic.php?f=74&t=9081#p45247
Lorenzo, newyd_cnc,
As in the reply on the forum:
Please include the drawing file associated with the:
NEWYD_MODEL_DECK_24cm.nc G-Code file.
I see indeed one leg missing of a TAB and I suspect that there are multiple arcs involved .
Regards,
CVH
Here's the QCAD file.
I understand that if a tab spans over two different entities there may be a problem. i don't think this is the case as the curve is a spline, not a set of overlapping arcs.
... and in anyway the tab algorithm should keep track of the number of Z ups and Z downs that it has generated and if the two numbers differ, should at least flag a warning.
I think the tab algorithm should be corrected to cope with this.
In files where several dozen tabs are used, it is indeed a problem if a few are incomplete as this can often only be spotted during cutting and that is a real shame.
regards
newyd_cnc
Lorenzo, newyd_cnc
The source entity is a polyline on layer '0'.
The TAB is near a vertex within 0.2611 units
And the two nearest segments are bulging or are arc segments.
Unless your cnc driver support Non-uniform rational basis spline (NURBS) ...
... Most G-code is limited to G0, G1 or G2/3.
Even the polyline is exploded to Line and Arc segments.
The workaround may consist of placing your TABs not near a corner or node.
Regards,
CVH
CVH I appreciate you taking the time to analyse my dxf file and finding a probably suitable the workaround for this very specific case. However I would love to see this bug fixed.
Designing a complex part for CAM work that normally happens much later down the line, one cannot plan the position of the tabs to ensure they are not close to nodes etc. The software should be able to compute tabs nevermind their placement on a closed continuous contour.
The cutting path that is created by qcad can indeed be executed , therefore the combined presence of lines, arcs and splines is not a problem. It is just the computation of where to place the z up and Z down that is buggy.
Besides, even without splines, tabs are often incompleted if near a vertex joining a line and an arc. This is as well a limiting bug that in my opinion should be elevated to "to be fixed" status.
As is, the user is left to find workarounds (and yours is surely a valid one ) and having to look deep into how the profiles have been drawn, the position of tabs relative to vertexes etc. I have cutting files with more than 150 tabs in them .... How can one substitute himself to a software function that should be made to work?
You are right that QCAD/CAM should cope with this.
But the report on the forum is from the beginning of 2022 and not the first on this matter.
As it is proprietary code I must restrict myself to workarounds.
Set to severity Low or not considered to be an issue that affects most users.
TABs are indeed essential to hold down your piece(s).
A missing G-code segment may corrupt the output completely.
My CNC driver would stop all movements and terminate critically.
Regards,
CVH