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Importing model from Altium creates slight deviations in tolerances (.00001 or less)

Question asked by Shea Nelson on Jun 28, 2018
Latest reply on May 5, 2019 by Shea Nelson

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I am working on an integrated electromechanical system and when attempting to mount boards modeled in Altium by my EE contractor, I have found that the angular relations are very, very slightly off. I am talking about 89.9995˚ instead of 90˚. This is a huge issue because it makes it nearly impossible to create mates as Solidworks finds a solution with the parts hundreds of meters apart. The only workaround I know of is creating my own planes in the models I receive and mating using those. Is there anything that one of us is doing wrong, or just some small check that will fix this?

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Daniel MCGINN Oct 23, 2018 3:44 PM
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Have an idea for an enhancement request? Consider posting your idea in the SOLIDWORKS World 2019 Top Ten List in the category "CircuitWorks/Electrical/PCB."
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- Shea Nelson @ Daniel MCGINN on May 5, 2019 1:47 PM
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  Thank you, Daniel!
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Keith Carter May 1, 2019 5:02 PM
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Shea,
Have you had a resolution to this issue? We have lately been seeing the same angle accuracy error.
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- Shea Nelson @ Keith Carter on May 5, 2019 1:48 PM
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  Hello Keith,
  Unfortunately I have no found a resolution yet, but luckily have not had to use any new models yet so my old "fixes" have held up for now. Have you made any headway on the problem?
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Ian McLean May 1, 2019 11:51 PM
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Shea Nelson wrote:

I am working on an integrated electromechanical system and when attempting to mount boards modeled in Altium by my EE contractor, I have found that the angular relations are very, very slightly off. I am talking about 89.9995˚ instead of 90˚. This is a huge issue because it makes it nearly impossible to create mates as Solidworks finds a solution with the parts hundreds of meters apart. The only workaround I know of is creating my own planes in the models I receive and mating using those. Is there anything that one of us is doing wrong, or just some small check that will fix this?
I have come across the same issue, I generally mate concentric to a mounting hole edge, the bottom face of the PCB and a parallel mate to one of the PCBA planes of the imported step file to get around the issue. There also seem to be issues with linear accuracy also , so other holes are frequently misaligned by 0.00001mm or so
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- Shea Nelson @ Ian McLean on May 5, 2019 1:51 PM
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  Hello Ian,
  That's a good idea, I'll have to try that mating scheme. I used mostly "band-aid" solutions but next time I get a model I'll try your idea when starting fresh. I remember seeing some linear accuracy issues too, but to the point where I couldn't measure it until adjusting the precision of the measuring tape accordingly. Frustrating!
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Mark Jeffrey May 2, 2019 3:49 AM
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Hi Shea
This isn't something silly like importing an imperial model into a metric assembly. Could be rounding errors on the conversion.
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- Shea Nelson @ Mark Jeffrey on May 5, 2019 1:51 PM
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  Hi Mark,
  Good thought for sure but unfortunately I'm pretty sure it's metric to metric. I will run it by my contractor though as the issue could be starting on his end.
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Marek Petrzilka May 2, 2019 9:07 AM
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Hi Shea,
I would suggest you to ask your contractor to give you PCB's models as *.STEP.
In our company we use Solidworks for "plastic boxes" and Altium for PCBs, I always get the PCB's model as *.step and I've never had any problem with mates.
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- S. Casale @ Marek Petrzilka on May 2, 2019 10:18 AM
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  SolidWorks works best with Parasolid.
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- Ian McLean @ Marek Petrzilka on May 2, 2019 4:23 PM
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  Just to clarify, we get step export from Altium and see this problem.
  It does not happen all the time, I would guess 5-10% of files we see issues with.
  I have seen the same issue with step files from suppliers.
  As far as I know STEP is the only neutral file format exported by Altium.
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Erik Bilello May 2, 2019 11:12 PM
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I note that this is a few months old, and we haven't heard from the OP since the first post, so maybe he's found a solution.
But, without knowing anything about Altium, the first thing that I would ask the OP is whether he can verify that the original model is accurate. If he sees this in a consistent manner, is it possible that someone is using a bad template to create the Altium models? I've encountered more than a couple of "bad importing" problems that turned out to be cases of accurate import of a badly made model. I've seen plenty of SW users who were "too busy getting important stuff done to worry about trivial details", or in other words, "sloppy". I'm not aware of any rule out there that says only SW users can be sloppy.
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- Shea Nelson @ Erik Bilello on May 5, 2019 1:55 PM
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  Hello Erik,
  I haven't found a solution yet but fortunately haven't had to make any changes to the assemblies with the PCBs in a while, not looking forward to when I do though! I think you might be on to something with the template, or at least something occurring on the Altium side of things. Someone suggested rounding errors on a metric to imperial conversion. While I am pretty sure the models I get are metric, my contractor might be using badly converted ones on his end. Thanks for the input!
  -Shea
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Importing model from Altium creates slight deviations in tolerances (.00001 or less)

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