- Status Assigned
- Percent Complete
- Task Type Feature Request
- Category QCAD/CAM
-
Assigned To
Andrew - Operating System All
- Severity Low
- Priority Very Low
- Reported Version 3.26.4
- Due in Version Undecided
-
Due Date
Undecided
-
Votes
2
- asicdruide (14.01.2023)
- CVH (10.11.2021)
- Private
FS#2307 - Tools to create dogbones or corner overcut
The inside corners of profile tool paths have rounded inside corners. This occurs because the rounded outside the bit cannot make it all the way into the corner of the feature. Think of tracing the inside wall of a cardboard box with a can of soup. The can makes direct contact with the box walls, but its
round shape is unable to completely fit into the tight corners— there’s always a gap.
In a dog-bone overcut (see the figure in attachment), the inside profile corner is enlarged into a semicircle, allowing the sharp edges of the mating piece to slide through without interference.
When a dog bone is applied to the inside corners, as shown in the second figure in the attachment, the joints fit together nicely!
The following website explains what should be implemented More elegant CNC dogbones
There are two ways to implement this tool. Either you modify the original design (as implemented in Fusion 360) or you can do it at the moment you define the tool path (Estlcam allows you to do this for example). See the feature Corner overcut, on Estlcam website
Screenshot from 2021-11-01 17...
I made a drawing to explain
Related to:
https://qcad.org/rsforum/viewtopic.php?f=74&t=8704
whenever you design for cnc milling, dogbones are really important for inner corners. A nice support there would be really helpful. The dxf format supports them natively. Just a nice interface would be needed.
asicdruide,
Please elaborate "The dxf format supports them natively"
IMHO there is nothing that is intended to support CAM details in dxf.
Regards,
CVH
Hello CVH,
in dxf it's named bulge and defines a circle-arc at the end of a line.
See e.g. here: https://ezdxf.mozman.at/docs/dxfentities/lwpolyline.html
Giving right parameters to them it's exactly what is needed for dogbones/corner overcuts.
I've already used that in script generated dxf-drawings for cnc milling.
In QCAD it could be implemented like the 'Abschrägen CH' or 'Abrunden RN' functionality.
Best regards,
asicduide
asicdruide,
True, Polylines can include bulging line segments beside straight edges.
Nothing new and true, we can exploit this to draw 'dogbone' shapes.
But there are some inconsistencies in your statement.
The bulging factor is how much the upcoming segment bulges out to left or right.
Zero for a straight edge and related to the arc sweep-angle: bulge = tan(sweep/4).
It can't be a circle because tan(360°/4) is an error.
If you set the last bulging factor of an open polyline nothing round will show there.
"At the end of a line" is not enough, you need at least two endpoints (nodes) to fully define the arc shape by the bulging factor and the arc chord what is the distance between the two nodes.
Remark here that the bulging factor is not related to an arc center point nor to an arc radius. For 'dogbone' shapes the cutter radius is also not accounted for.
Besides specific parameters for the arc shape the two adjacent segments must be altered ... trimmed.
So the dxf format supports arc segments natively but not 'dogbones' in direct.
This is all about the outline of the 'dogbone' shape .. The cutted area.
And not about CAM or the cutter trajectory.
The outline is of lesser use as long as QCAM doesn't support pocketing.
Indeed, it could be implemented as RN but the most simplistic slot has four corners.
Rather something automated instead of indicating 4 times a combination pair of entities or segments.
But there is more to it: Inside angles can vary from 90°, neighbors can be arc segments themselves. For common 'dogbones' and 'T-bones' the cutter trajectory exhibits various discontinuous motions especially a full stop and reversing for the overcut itself.
Some extra clearance, a perfect fit or hammer-tight ...
Working on it but don't hold your breath.
It won't be a part of the proprietary QCAM package mastered by Andrew.
For now neighboring arcs are still an issue, Bulging doesn't always transform perfectly into arcs and tangentially connected arcs don't always play nice.
This has a lot to do with the difference between endpoints and ending angles ... The maths are never perfect.
Regards,
CVH