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Strange behavior in assembly linear pattern

Cris_BowersCris_Bowers Member Posts: 239 PRO
I was looking at an IR request for a centered option for an assembly linear pattern. I thought this was possible by just selecting opposing directions to pattern in. But when I tried it, I got unexpected results:
First by patterning a part with 2 instances in either direction, I end up with 3 instances in the patterned feature with an instance being recreated at the seed part location.

Next I tried 3 in one direction and 2 in the other. This time I end up with 5 instances in the pattern. 1 extra instance at the seed part location and another at the part above it. 

And finally I tried 3 instances in each direction and ended up with 8 instances in the pattern. Numbering the part positions in the graphical area from top to bottom as 1-6, the items listed from top to bottom in the tree are position 2, 4, 3, 1, 2, 6, 5, 3. As you can see the parts at position 2 and 3 have been repeated.

It only gets compounded if you choose a 3rd direction. I chose to pattern 2 instances away from from the face of the extrusion. If I counted the parts on my screen I only see 10, but 17 parts were listed in the tree. Solidworks gets around this strange behavior by adding an option and even throws up a warning to select "pattern seed only". This option ignores the rest of the instances in the pattern and only patterns the seed feature. So if I choose to pattern 2 instances north and 2 instances south, I would have 2 instances in the pattern, one above the seed and one below.

Comments

  • patrick_farleypatrick_farley Member Posts: 32
    I think Onshape calculate the seed as one. its fine until you go into your case

  • Cris_BowersCris_Bowers Member Posts: 239 PRO
    Yes, the seed is calculated as an instance. This is where I was commenting on how Solidworks handles patterning in parallel directions by warning the user to check the "pattern seed only" check box. The problem arises when the distances chosen are the same value because an instance will be created at the seed position and essentially be invisible.

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