Rotating tabs - inconsistencies

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Rotating tabs - inconsistencies

georgesbasement
Here I am, faced with a bunch of entities to cut out of a metal plate by either of two techniques: water jet cutting or laser cutting. In either situation the plate is held by the edges. If the process cuts all the way around any one object, it will fall out of the hole and down into what amounts to oblivion, that is, it will likely get lost.

Therefore, I have to leave an uncut tab on the periphery of every object so that it will remain attached to the plate.

So far, I have managed to create a series of blocks, each one depicting a tab pointing in a useful direction. This effort is not without its problems. The main one is that when I attempt to open and modify a tab and then create another named tab from it, thereby being given the opportunity to name the new tab, I find that after I have closed what I think is the new tab, I find that I have modified both tabs and now have two identical tabs with different names.

How to I turn the original tab back the way it was originally pointing ? I find that both "Move and Rotate" and "Mirror" produce unpredictable outcomes. Sometimes "Mirror" rotates my tab by an uneven multiple of ninety degrees. I don't know what is the meaning of "angle" in this context - on an absolute polar-coordinate system or just relative, applied to the object's desired motion.

What's worse, now I've discovered that four out of six versions of this tab have gone blank. They will have to be re-created ... but I have lost all confidence in how to accomplish that. I need six more positions on my compass, 45 degrees apart.

On top of that, I find that editing a tab (from the list of tabs) changes all instances of that tab that have been put in my drawing, so I have to create and finalize all the desired tabs before ever starting to use them in my drawing.

Best regards,
georgesbasement
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Re: Rotating tabs - inconsistencies

mad-hattter
Hello.
 
A block when saved is just a *.dxf drawing.
One way :-
Draw your 1st. tab with a useful origin and save it somewhere. (myTabName)
Now open your main drawing.
From the librecad menu – select file/import/block, select myTabName, you will then be prompted where to place it.
It will appear on you drawing and in in the block list.
Now repeat the import, position it, it will appear in you block list as myTabName1.
Repeat for as many tabs as you want.
Each tab is now an entity and can be edited/rotated/etc.  as you want without changing the others.
 
Regards
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Re: Rotating tabs - inconsistencies

grherr
In reply to this post by georgesbasement



On 08/09/2017 09:20 AM, georgesbasement [via LibreCAD] wrote:
Here I am, faced with a bunch of entities to cut out of a metal plate by either of two techniques: water jet cutting or laser cutting. In either situation the plate is held by the edges. If the process cuts all the way around any one object, it will fall out of the hole and down into what amounts to oblivion, that is, it will likely get lost.

Therefore, I have to leave an uncut tab on the periphery of every object so that it will remain attached to the plate.

So far, I have managed to create a series of blocks, each one depicting a tab pointing in a useful direction. This effort is not without its problems. The main one is that when I attempt to open and modify a tab and then create another named tab from it, thereby being given the opportunity to name the new tab, I find that after I have closed what I think is the new tab, I find that I have modified both tabs and now have two identical tabs with different names.
Did you just copy a block to another instance in the drawing (i.e. using ctrl-C, ctrl-V) and edit that pasted instance?
If so, that may be why all instances are being changed when one is edited. What I do is to save the active block to a different filename (block name). While in the "Block List" dialog, select the block you want to copy and edit from the list, then click on the floppy disk icon ("Save the active Block to a file") and in the dialog, select the directory and filename (block name) you want the new block to reside. Make sure the directory is where your library blocks are stored. You can determine that path with Options | Application Preferences and select the "Paths" tab. There you should have listed the paths LC looks in for items. The "Part Libraries" box should tell you where the blocks are stored. Keep in mind that this path is in addition to the LC default library path. Both will show up in the "Library Browser" listing. I have my own library path in this box and I still get the LC library in addition to mine in the browser. Once in the correct location, you should be able to instantiate the new block (file) with the Library Browser and edit it. The source block should not be affected, since it is a different name.

A note on block filenames: LibreCad postfixes a "-n" to each instance of the block you instantiate and it does not discriminate! If you end the file name with a number, LC will take over that number as an instance number. You can see the instances in the Block List. So, do not end your filename with "-1" for version one, or "-90" for 90-degree, etc. I have blocks that have "-45" for a 45-degree version, and LC used the "-45" as the first instance and "-46" for the second, etc. I found that if I postfix an underscore, then LC will not take over my number. For example, "-45_" will become "-45_-1" etc. It's a kludge, but it works.

How to I turn the original tab back the way it was originally pointing ? I find that both "Move and Rotate" and "Mirror" produce unpredictable outcomes. Sometimes "Mirror" rotates my tab by an uneven multiple of ninety degrees. I don't know what is the meaning of "angle" in this context - on an absolute polar-coordinate system or just relative, applied to the object's desired motion.
Have you tried "Undo" (ctrl-z) to restore stuff that didn't work as expected?
Just remember undo is useless if you exit LC or close the document. All is forgotten then.

It sounds like you might be using the command line to rotate and mirror objects, entering the point and reference values as numbers. I use the mouse, and for mirroring, I select one reference point and a second reference point shows on the screen as the end of a line. That line emulates a mirror, with the selected entity to rotate ghosted in as a reflection in that "mirror". If I don't click the second point and I move the line end around with the mouse, the ghost also moves around, representing the result when I clicked the second point. Selecting a second point orthogonally opposite the first point, produces a 180 degree mirror. It works for me every time. The mirror points do not have to be in a specific location from the object, just on the side you want the mirror to occur.

The Rotation process is different. I select Tools | Modify | Rotate, and a big cross shows up to select the entity to rotate. I click on the entity and "Enter" to stop the selection. At the bottom of the window, a prompt shows to "Specify rotation center". I click on the entity's center of rotation and it then prompts to "Specify reference point". I usually click the same point as the rotation center, but I am sure there may be some reason to separate them. Grid Snap is your friend. Then a dialog comes up with the rotation angle box, a selection to delete or keep the original (I usually delete the original) or make multiple copies, and whether to use the current attributes or current layer. I keep both of the latter unchecked and it seems to work. Remember that the rotation angle is counter-clockwise from the current position. The little arrow on the dialog icon reminds you of this. Clicking on "Okay" should produce the correct results.

What's worse, now I've discovered that four out of six versions of this tab have gone blank. They will have to be re-created ... but I have lost all confidence in how to accomplish that. I need six more positions on my compass, 45 degrees apart.

Ahhh! I see that bug when I copy-paste an area containing blocks to another drawing (sheet). All of  the pasted blocks appear at first, but then some later disappear! Usually, it happens after I have done something, like move something, not necessarily something in this pasted area. I have not discovered a work-around for this and I have not yet posted this problem to this forum to see if anyone has a workaround. It is frustrating. Maybe LC 2.2.x will have fixed this too.
On top of that, I find that editing a tab (from the list of tabs) changes all instances of that tab that have been put in my drawing, so I have to create and finalize all the desired tabs before ever starting to use them in my drawing.
Yes. See the procedure above. You need to create a separate block for each difference, not edit an existing instance of a block. That is, if you don't want to do separate rotations as in your case. You should be able to rotate one instance without affecting the other instances of the same block. But if you want a "canned" version that can be instantiated without modification, then you need to create a separate block file for each version.

Best regards,
georgesbasement


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NAML
HTH.
Girvin Herr

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Re: Rotating tabs - inconsistencies

georgesbasement
Neither of the previous two sets of suggestions works for my drawing, which consists of almost seventy discrete objects; plus another drawing also in the works, and three candidate vendors waiting for updated files ...

I appears that what I will have to do is create Tab-A, save it in my Blocks folder; close it; close LibreCAD; reopen LibreCAD, create another tab, rotate that new another position, save that under a new name, etc, etc. until I have eight such tabs. Then I should be able to import each tab, apply it as many times as needed, save the main drawing under a new name, proceed to Tab-B, etc., etc. with as many overlooked positions as remain to fill in until every object has a tab and they all stay put.

If "Rotate" were a separate menu item, this might be easier, but that is for a later version. The developers probably had an entirely different application in mind when they wrote this code, and I cannot fault them for that.

Best regards,
georgesbasement
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Re: Rotating tabs - inconsistencies

georgesbasement
Getting past all the various inconsistencies, I have managed to create eight differently oriented tabs, angularly spaced around the compass, but I've put them into their own "Blocks" folder within my "Drawings" folder.

I can import one such block into my main drawing, but when I try that from the next block in my list, LibreCAD puts it in with the first one along with several opaquely named copies, some of which are blank, and renames most of what's there. When I ascertain which ones I want to keep and delete the rest, I find that all but one of the remainder are now blank. If I were to leave well enough alone, I would end up with umpteen copies, blank files, etc. from which I would have to again ascertain which ones are useful and make up my own scorecard in order reliably to pick them out for later insertion at the appropriate places in my drawing.

Is there a less tedious way of doing this "tabulation" of my drawing ?

Best regards,
georgesbasement
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Re: Rotating tabs - inconsistencies

georgesbasement
Plunging ahead, I imported each of eight tabs into my drawing, edited each appropriately so I could be sure that each possesses a reference point, I find that only one of the blocks can be pasted into the drawing. All the rest both fail to indicate their reference point or basic shape, but also fail the import procedure, with blank result - my drawing has no newly imported tab.

Dead in the water,
Best regards,
georgesbasement
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Re: Rotating tabs - inconsistencies

georgesbasement
In reply to this post by georgesbasement
Correction: There is indeed a "Rotate" menu item, and it is faster & easier to use than "Rotate, Move."

My apology to the developers.
Best regards,
georgesbasement
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Re: Rotating tabs - inconsistencies

dellus
In reply to this post by georgesbasement
If the the overall drawing isn't too complex, it might be easier to dispense with using blocks and doing the rotation and editing / adapting of the single tabs simply in that main drawing. Later then you can isolate  / copy these single tabs into extra drawings (files) for each one to send to the cutting service.

By the way, as you where talking of that sleepy eye icon with eyelashes, it seems you are not using the latest stable version, which is 2.1.3. Some bugs annoying you may have been fixed.

If you provide a drawing file of what you already have achieved and a sketch of what you want in the end (a scan or photo) I could help you with the drawing.
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Re: Rotating tabs - inconsistencies

georgesbasement
Thanks to dellus for mentioning that there is a later stable version of LC than mine. I have been checking Trisquel's software update & upgrade functions, but that branch of Linux, which is based on Ubuntu, but from which every shred of proprietary (non-free, per the Free Software Foundation) software has been removed, hasn't yet caught up. In the meantime, I'm not aware of any troublesome bugs ... just slow learning on my part.

In the morning today, having recovered a little from my case of sleepy eye, I went back a little and studied one of my earlier posts and re-learned the procedure for creating blocks. What has been successful for my most recent drawing (various brackets and links) for the same project is that I opened each of my (not-yet-block) blocks (those of the eight compass orientations) for edit, selected the "Create Block" icon from the left-side toolbar, then used "Select All" from the upper-edge toolbar, picked a reference point, and then saved the newly created _real_ block with a (slightly) new block name.  Once I did all eight blocks, I could then select them one-at-a-time and use the "Import Block" item from the "Block" menu to poke the selected block into appropriate places on the drawing. I could then adjust the positions of the resulting tabs to be closer to the outlines of the selected objects. Putting the block/tabs onto all of the objects in the drawing took less than ten minutes. Adjusting them will take a little longer. These are destined for laser cutting from a sheet of quarter-inch-thick steel flat stock.

Thanks again,
Best regards,
georgesbasement
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Re: Rotating tabs - inconsistencies

georgesbasement
Continuing to a successful conclusion, I became more familiar with the "Snap" functions, "Rotate", "Rotate & Move", etc. and the importance of "Save." Even "Copy" and "Paste." The latter became necessary when LC quietly (off my expanded view of the drawing !) deleted major portions of the end curves on a couple of my objects. "Undo" was past "do" so I found I could draw an arc with three points on top of another example of the same curve and then select it (right on top of the original curve !) and move it with copy and past to repair the damage without affecting the original curve.

Rotating, moving, and patching in the tabs was fraught with inconsistencies because the transitions could never be perfect, and so I had to connect the fillets at each side of the tab with straight lines between points placed on the fillets and on the curve or straight side of the object.  All eight of the different orientations behaved OK, but I found one object which flat out refused to let me delete the unwanted curve between the two fillet curves & their extra patch-in lines, so I just deleted it from the object and put another tab at a different position.

Sometimes, "Divide" worked great: I'd select the command, click on the unwanted portion between the two fillets, etc., and then select the two intersections at the ends of the unwanted portions, whereupon the unwanted portion would disappear ... or at least turn blue, waiting for me to use "Select Entity" and "Delete" to get rid of it.

Sometimes, this procedure would cause part of the main object to become unselected, and in those instances I found that I could sometimes use "Trim" on the not-unselected portion of the object with one of those added-in straight lines as the cutting entity. Then, clicking on the not-unselected portion of the object would cause the unwanted section between the fillets to become deletable. Sometimes this attempt would crash LC, and I not-quickly-enough learned to save after each successful step, or I'd be faced with the tabular guessing game again.

"Trim 2" was most likely of all to cause crashes, and I don't remember getting any positive result with it. Plenty of other tools did work, however.

I now have a completed .DXF drawing with 32 objects and their quite shapely tabs sticking out in all directions; there are a half-dozen tiny gaps remaining in some of the transitions between arcs and straight lines, but those are easily fixable in the morning after a good night's sleep.

Thanks for all your very useful help & advice.
Best regards,
gergesbasement
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