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Face Mirror vs. Face Pattern Behavior
Makoto_Nara
Member Posts: 2 ✭
Have an issue where a face mirror is failing to regenerate and I am a little confused as to why as attempting to do something similar with a face pattern works. Apologies in advance if this is a well known issue, a couple google searches and a search through the onshape forums did not yield a similar question (but I wasn't 100% sure what to search).
Here is a test part studio where I made an extremely simple example: https://cad.onshape.com/documents/6c23fbdbfd8ffc196040db6e/w/9a6ff10f8c362454572ed2f4/e/33f6e5669233f4db62550ae8
The issue is that this mirror fails when I try to mirror these three faces across the right plane, creating a symmetrical notch:
However, attempting the same process with a linear face pattern is successful. This is confusing as it indicates a problem with mirror rather than with the underlying feature/faces that I am trying to mirror. Does anyone have insight into why this might be a problem and what I should do differently? There are several workarounds (like the linear pattern) but the mirror is a lot cleaner, robust to changes, and thus preferred.
Here is a test part studio where I made an extremely simple example: https://cad.onshape.com/documents/6c23fbdbfd8ffc196040db6e/w/9a6ff10f8c362454572ed2f4/e/33f6e5669233f4db62550ae8
The issue is that this mirror fails when I try to mirror these three faces across the right plane, creating a symmetrical notch:
However, attempting the same process with a linear face pattern is successful. This is confusing as it indicates a problem with mirror rather than with the underlying feature/faces that I am trying to mirror. Does anyone have insight into why this might be a problem and what I should do differently? There are several workarounds (like the linear pattern) but the mirror is a lot cleaner, robust to changes, and thus preferred.
0
Answers
However, I made a really simple model of something similar and honestly I do not know why a Face Mirror fails. I wouldn't normally use one for something this simple - I would be more likely to do it in the sketch itself or just mirror an Extrude/Remove feature, not its faces. That said, part of the reason is that Face Mirrors are often very picky, and in this case it seems silly. What I can see is that face mirrors that don't break any edges of the existing topology - e.g. an internal round hole - will work. Mirror 1 is trying to mirror the 3 faces of the notch - it fails. Mirror 3 mirrors the cylindrical face of the hole. It works.
Here's the file in case any one wants to look at it:
https://cad.onshape.com/documents/5a99ec6b89b52bf574bfdb29/w/dabf50fe2c0eaecbcc27c974/e/33109e1727397a1a38c6a1dc
That's one workaround that is good to know for other use cases as well.
They are the quickest to compute but because of this aspect not very robust. One identity change upsteam and they fail.
so in this case, because the middle slot interupts the face at the top, the mirrored faces are interacting with a new top face, rather than the same one.
You could check this by reversing the order of the features and put the middle slot downstream of the mirrored slot in the feature tree. i'm betting it will work then.
a 'feature' mirror pattern is probably more robust. if you set it at 'reapply features' it will be slow but robust.
Nicks option is also very robust. set the original feature to "new" and mirror/pattern the new part and subtract there or later. Very robust but it does take more compute. (which may not be an issue at all for a simple part).