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Mirrored component non concentric in 2011SP3/SP4 (ok in SP2)

Question asked by joel Dwyer on Jul 29, 2011
Latest reply on Oct 28, 2011 by Wayne Tiffany

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This is driving me nuts. I created an assembly in 2010. Time goes by no issue. Fast foward to 2011 SP3 and my mirrored part is now nonconcentric. If i open in SP2 and save all is ok. If i open in SP3 or 4 and save it goes non concentric. My reseller tells me it is because SW uses center of gravity to mirror. Im not satisfied with this answer for the obvious reasons. Ive got lots of time into an assembly that i cant use anymore. Reseller says they will alert me of SR status.

Please help. Im getting frustrated with my resellers confidence in themselves.

Wayne Tiffany Aug 4, 2011 8:39 AM

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This is a good response - someone at SW that says they will personally put an eyeball on this.

I just ran into this again yesterday. One of our guys called me over to show me this weird thing that SW was doing. He mirrored a part in an assy and then changed the config of it to one that had an edge cut off for clearance on that end of the assy. When he changed the config, the part moved. The mounting face that was mated should have stayed in the same location, but the "COG" movement pushed the part into the mating part. Not good.

Hopefully this will be resolved as the way it is makes the mirror functionality less usefull and possibly creating errors that will bite people if they don't catch the fact that the mirrored part is off a bit.

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Wayne Tiffany Jul 29, 2011 1:51 PM
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Edit the mirror feature and choose mirror 2, not 1. It appears that the holes are maybe not quite symmetrical or something. Why you see a change between SP2 & 4 I don't know - it would be worth turning that in to see if SW has that answer.

The thought of mirroring about the CG doesn't make any sense to me when you specifically tell it to mirror about the plane.

WT
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- joel Dwyer @ Wayne Tiffany on Jul 29, 2011 2:16 PM
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  OK, so if you supress any nonsymetrical features in this parts it goes concentric. Once you reintroduce them it goes nonconcentric. It does seem to be affected by COG however counterintuitive it may seem. Also the fact that this only happens it SP3/4 is indicative of something fishy.
  
  This is the only data i can find on how mirror centers work. Now according to this diagram the COG is the defining position relative to the mirror plane. Is it also the definig position relative to other planes? It does seem so, i think this is an error
  
  SW has not responded to my SR yet, but again my reseller seems to think all is ok which is frustrating the crap out of me.
  
  LOCATED HERE
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  - Kelvin Lamport @ joel Dwyer on Jul 29, 2011 3:25 PM
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    This is just plain wrong!
    
    When a part is designed it is designed around the origin, the COG is what it is. I usually don't give a damn about the COG. If I mirror a part (regardless of orientation) I expect that part to be based on how the part was designed, i.e. the origin, not some arbitrary COG which could change whenever the design changes.
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    - Wayne Tiffany @ Kelvin Lamport on Jul 29, 2011 5:25 PM
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      Absolutely! Since we are allowed to change the config of the mirrored part, which is a good feature, then the mirrored part may have all kinds of stuff that changes and its position should be relative to the origin. I'm pretty sure it used to work this way.
      
      WT
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Bill Hamze Jul 29, 2011 7:41 PM
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Interesting topic. I've never experienced this myself so I decided to experiment. The problem seems to be isolated in the assembly level. When mirroring in the part level the body's remain concentric, regardless of any nonsymmetrical features (at least with my testing). In the assembly, we could dissolve the mirror feature and use mates to make the parts concentric. I'm sure there are other methods/fixes but we shouldn't have to go that far. I'm not sure if SW uses the COG to define its mirror but I have to agree with Kelvin..."the mirror should be based on how it was designed". Let see what other members come up with.
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- joel Dwyer @ Bill Hamze on Aug 1, 2011 10:06 AM
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  My Reseller insists this is ok and will not submit to SW. What do you guys think? And how would i subvert my reseller and go directly to SW. Can i do that?
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  - Kelvin Lamport @ joel Dwyer on Aug 1, 2011 10:21 AM
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    You already have by starting this thread.
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Patrick O'Hern Aug 1, 2011 10:25 AM

I've noticed this same thing recently and it was bugging the crap out of me too. As a workaround, I created an axis along my mirror plane and did a circular pattern with two parts @ 180 degrees. I didn't contact my VAR about it, but that's mainly because I'm stuck in 2010 for now and was hopeing it was something 2011 would have fixed already...

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joel Dwyer @ Patrick O'Hern on Aug 1, 2011 10:28 AM

Knowledge base info related i think? This is not very clear to me:

Solution Id:	S-09957	Category:		FAQ

Question:	Why are mirrored components rotated to unexpected angles after using the mirror component command when the "left/right version" box is not checked?		Keyword:	Components

			Visible to Customer:	Yes

			Link:


Answer:	When using the mirror component, SolidWorks will place a component on the other side of the mirror plane as a mirror of itself if the component is symmetrical (i.e. the part can be rotated to appear as a mirror image of itself). If the user chooses to place a copy on the other side for components that are asymmetric (i.e. parts that cannot be a mirror of themselves), the orientation that SolidWorks determines could appear arbitrary as SolidWorks attempts to create a "best fit" by rotating the new instance of the component to a similar orientation as the original component. This orientation is computed based on the centroid and principal axes and may lead to unexpected orientation of components. Consider using pattern instead of mirror, to maintain the orientation of asymmetric components.

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Wayne Tiffany @ joel Dwyer on Aug 1, 2011 6:47 PM
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I think this means that the action you are seeing is intended. Therefore the option here is to generate an enhancement request and we will vote for it.

WT
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- joel Dwyer @ Wayne Tiffany on Aug 3, 2011 9:09 PM
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  SW Response Below. Seems to me this is the logical way for it to work, however it clearly does not work this way. If a bounding box center was indeed the reference point for all axis' then mirrored components would have no movement relative to each other when features are introduced that have no affect on the bounding box geometry, however this is not the case. I does seem to operate off COG.
  
  Thank you for your feedback. We apologize for the issues you are experiencing.
  
  There are inaccuracies in the help topic which, unfortunately, could not be corrected in time for inclusion the 2011 help. The following appears is the Release Notes for SolidWorks 2011:
  Orientation of Mirrored Instances
  The help topic "Example - Orientation of Mirrored Instances" contains some inaccuracies. It should state the following:
  For one orientation, the mirrored component is positioned based on the seed component's bounding box. That is, for both components, the center of the bounding box is the same distance from the mirror plane, and three virtual axes in the space (axes in the directions of components’ axes and with the origin at the bounding box center) are at mirrored positions. To achieve the other orientations, the software flips the mirrored instance about its bounding box center in the x, y, or both the x and y directions.
  I have pulled the topic out of the help for SW2012. I plan to add it back in after I thoroughly research it, confirm the functionality, and update the topic.
  
  I hope the above information helps to resolve your problem, or at least understand why it is happening. I will also bring your forum postings to the attention of our User Experience group.
  
  On behalf of the SolidWorks Documentation Team,
  Regards,
  Joan
  Joan Hurton
  Principal Technical Writer
  CSWP - Certified SolidWorks Professional
  
  Visit us at: www.solidworks.com
  DS SolidWorks Corp - 300 Baker Avenue - CONCORD, MA 01742, United States
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  - Wayne Tiffany @ joel Dwyer on Aug 4, 2011 8:39 AM
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    This is a good response - someone at SW that says they will personally put an eyeball on this.
    
    I just ran into this again yesterday. One of our guys called me over to show me this weird thing that SW was doing. He mirrored a part in an assy and then changed the config of it to one that had an edge cut off for clearance on that end of the assy. When he changed the config, the part moved. The mounting face that was mated should have stayed in the same location, but the "COG" movement pushed the part into the mating part. Not good.
    
    Hopefully this will be resolved as the way it is makes the mirror functionality less usefull and possibly creating errors that will bite people if they don't catch the fact that the mirrored part is off a bit.
    
    WT
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    - joel Dwyer @ Wayne Tiffany on Aug 4, 2011 8:44 AM
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      Seems for those more experienced the general rule is to stay away from the component mirror command. I was warned by an employee with more experience w/ SW when I started the project Im having the issue with now. This is clearly not news to users and SW alike (mirror issues).
      
      As for slightly off, the smaller the part is the more extreme COG movement will be. I have an assy off by more than 1/8" I have to keep a machine running with SW 2011 SP2. when im done working and before i submit to a customer i go to the machine, open the assy and dwg, rebuild and save...PITA
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      - Tom Drechsler @ joel Dwyer on Aug 10, 2011 12:01 PM
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        I am having the same issue in SWX10 SP2.0 Of two parts, the truly symmetric one has no issues & the apparently symmetric one with a skewed COG does.
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        Kelvin Lamport @ Tom Drechsler on Aug 10, 2011 12:17 PM
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        I guess the lesson to be learned here is to not use the Mirror function for anything other than for creating opposite hand versions.
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        joel Dwyer @ Kelvin Lamport on Oct 27, 2011 9:00 AM
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        Solidworks response to this issue in 2012:
        Remove page in help menu that shows mirror instance selection working correctly. This still does not work properly in 2012. I am stuck on 2011 SP2 and VAR wants to know if we will renew our subscription....This stinks. No response from solidworks either other than a technical writer telling me she will look into it 6 months ago.
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        joel Dwyer @ joel Dwyer on Oct 28, 2011 1:44 PM
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        A satisfactory answer...finally:
        
        Hi Joel,
        
        Joan forwarded your question to me, and I have researched the history on this.   I apologize for the confusion on this subject; it was not communicated properly.    Below, I’ll explain what I have found. I expect you will still be unsatisfied, but I hope the explanation will help bring this to resolution.
        
        The behavior you see in SolidWorks 2011 SP3 and SP4 is the same behavior we had back in SolidWorks 2010. The component is located about the mirror plane using Center of Mass and then rotated through 4 possible alignments. That method has problems, as you and others have noted on the forums. So, in SW2011, SP0, we implemented a solution – to use the center of the bounding box of the model instead. This solved some of the problems, and it works better for your example. Unfortunately, it created other problems that caused regressions at other customers. To see one simplified example of that, please see the attached. In SW2011 SP2, a Control+Q will cause the mirror to fly away from the seed. In SW2011 Sp4, it is maintained as it was defined in SW2010.
        
        Because of regressions like this, the difficult decision was made in SW2011 SP3 to revert back to the SW2010 behavior. That was the majority case because of the adoption rate of all service packs of SW2010 compared with SP0,1, and 2 of SW 2011. As you found in your investigation, the documentation lagged, and that further confused the issue.
        
        The original problem remains, so there is still an open SPR to review the behavior – SPR534601. I’ll add you to that SPR so that you will be notified when it is addressed. At this time, the issue is still open and a complete solution has not been found.
        
        If you encounter this often, then an alternate approach is to use the mirror to bring in the mirrored component and then dissolve it. Once you do, you can use mates, including the symmetry mate, to position the components using logic you control completely.   I hope this explains the events and gives you guidance on how to proceed.
        
        Best regards,
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        Wayne Tiffany @ joel Dwyer on Oct 28, 2011 2:09 PM
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        So I still wonder why the mirror is not happening relative to the origin of the part being mirrored. Seems to me that the system planes of the part would be the most stable, repeatable, and satisfactory. Mirroring about the CG is about the worst thing I can think of as even small changes to the mirrored config will cause it to move.
        
        WT
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        joel Dwyer @ Wayne Tiffany on Oct 28, 2011 2:13 PM
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        Here is the attachment sent with the email above.
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        2010_sample.zip193.6 KB
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        Wayne Tiffany @ joel Dwyer on Oct 28, 2011 3:22 PM
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        I so applaud SW for making the mirroring an editable feature - it made the mirroring useable for the most part. But the mirroring as seen in the 2010_sample is hardly usable as the mirrored part isn't even close to a proper position. But if the mirroring happened per the origin, it would work just fine.
        
        WT
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        Glenn Schroeder @ Wayne Tiffany on Oct 28, 2011 2:17 PM
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        Wayne,
        
        You're right, it should use the Origin and not the cg. On the other hand I have to give the folks at SW credit for changing the Mirror Component function in SW2010 so that the mirrored components were fully defined and it was possible to go back and edit the function. That was a huge improvement over SW2009.
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Mirrored component non concentric in 2011SP3/SP4 (ok in SP2)

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