Here I am, attaching tabs to a bunch of circle drawings so the resulting disks won't fall out of the workpiece being laser cut. One tab needs to be rotated so its fillets will ever-so-slightly intersect the circle, so I can remove the short arc remaining with "Divide." This has been working like a charm for the last dozen or so tabs ...
Suddenly, one tab that I've just patched into the circle refuses to be selected for one last "Rotate" operation, in spite of my "Snap" settings. Changing the "Snap" settings didn't help.
Instead, I chose to make the circle and its tab into a block. Then I selected "Create Block" in the "Block" menu at the top of the screen, turned the circle and its (incompletely) attached tab into a block, selected that block for edit, completed the editing of the block, and closed it ... Yippee ! There is my block/circle, sitting in the correct place in my drawing of umpteen circles, complete with attached tab and with the unwanted arc gone.
In several other instances, I found that a few circles and their properly attached tabs had to be rotated so as to make the tab project properly into the minimal space between surrounding circles so that the tab could perform its function of preventing loss of the nearly detached disk during laser cutting without making the later separation of the disk from the workpiece awkward.
I again used the "Create Block" function to turn the circle and its properly attached tab into a block, saved it, and then rotated the entire block as a complete entity. That allows the tab to be rotated and translated with the circle without separating the unwanted gap from the tab as the circle was rotated.
Very versatile, this LibreCAD program is !
Thanks to its developers.
During the process of attaching tabs to the circles, making blocks of some of them so as to re-orient the tabbed circle in order to locate the tabs of adjacent circles as far apart as possible, I came across one circle from which I could not remove the short arc separating the tab from the interior of the circle. "Divide" would not let me select that arc as the portion I wanted to remove. I even created another block from the circle and its attached tab, but even editing the block as a separate entity did not work. Eventually I found another circle of the same size, erased the reluctant circle and its attached tab from my drawing and then inserted the second circle (previously turned into a block of its own) and then re-oriented it to the correct position, and all was copacetic again.
What I had done to bring this awkward situation upon myself was this:
While creating the drawing I placed the required circles (mostly a number of different sizes, about half duplicates) and ended up with a trapezoidal pile. I then noticed that if I made that pile into a block of N dissimilar circles, I could reinsert that block into the upper half of my drawing, rotate the block 180 degrees, and then it would fit right in so as to complement the existing trapezoidal pile. I did have to stretch my workpiece square plate into a rectangular shape,
Following that move, I discovered in the process of inserting all the tabs of various orientations that I had to move some of them around in order to eliminate some overlaps. Midway in that process I discovered for myself what the term "Explode" means in LibreCAD: disconnect the various parts of the block into separate entities.
Late in this effort I found that there was one last tabbed circle within which I could not get "Divide" to function.
Then the light dawned (literally) once again, and I "Exploded" the reluctant circle (by now a block of its own) and discovered that "Divide" was at last functional again. I now must remind myself that the four main functions of mathematics are: to add, subtract, multiply, and "Divide."
Evidently, insofar as "Divide" was concerned, the entity to select was still part of the original, multi-circle block, and I wasn't "Selecting" in the right place; I kept getting an error message to the effect that the entity to select must be part of an arc, line, or other such element. "Somewhere-Else Block" isn't part of that elite group. "Exploding" that little block made those parts eligible again.
Which brings up a question, perhaps related:
Once I have managed to remove the unwanted arc from my tabbed circle, there are sometimes little attached "tails" of the tab's fillets that extend short distances inside the circle. When I try to cut them off with the "Trim" function, I am allowed to nominate the cutting entity, but then "Trim" won't let me select the desired portion of the fillet as the "Trimmed" entity, again telling me that it is not part of an arc, line, etc.
Will "Explode" release "Trim" from its bondage as part of the "Somewhere-Else Block" ?
I could not get "Explode" to change my drawn fillets into a "Trimable" configuration, but I found an avoidance mechanism and a (somewhat laborious) workaround/repair method.
Here's the progress to report:
1. It would have been much easier to create eight tab-blocks as pairs of short parallel lines in the eight compass directions, then import those blocks as appropriate and connect the fillets to the objects with the 3-point, "Draw Arc" function. The transitions from the two fillets to the object would then not have any over-runs, so long as I place cutting points on the object drawing beforehand and use the "Snap On End Points" setting.
2. What I did manage to achieve was to rotate the tabs whose fillets run inside the object so that a tiny section of the object's outline intersected the fillet in two places, allowing me to use "Divide" to remove that intersected portion of the outline without getting a significant undercut during the cutting process. That leaves a short piece of the fillet curve _outside_ the drawing outline where it will not remain as a "feature" in the part after the cut is complete.
My concern was never to leave a dead-end laser cut inside my objects, as it might act as a notch. Notches in the waste aren't going to bother anyone, although the cutting machine might try to follow those dead ends anyway.
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