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Surface Profile - Iterate and Repierce function

Can someone give me a rundown of what the iterate and repierce function does? I turn it on and all of a sudden my surface profile improves significantly. Is that real?

On a similar topic, has anyone else had trouble with vector least square best fit causing a best fit error? I have had several parts now that had profile dimensions set to vector best fit, which runs fine offline, that have given me best fit errors at the end of the program. If I hunt down the offending dimension and change it to least squares the error goes away immediately. I have also had a similar problem if I set the iterate and repierce function with too small of a tolerance. I'm using an .039 (1mm) ruby and have found I need to set the repierce tolerance to at least .025 to reliably run through the program without any best fit errors. This seems to be related to features with very large radiuses of contour (almost flat, but not quite). My assumption is that the math runs out to too many decimal places and it can't handle it.

Thanks for any advice. I am inspecting a part that is just one giant contour, no flats at all, and need to have all of my ducks in a row around how all of the surface profile options work.
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  • Ok, I'm going to answer my own question here based on some experimentation and give myself, and anyone else who might come along later, some advice:

    What does it do?: It seems to work like a mini iterative alignment for your profile dimension. It will take your measured points and move them around on the CAD model within the tolerance zone you allow. It moves, pierces, iterates, re-pierces, and reiterates until it hits your maximum allowed iterations. Then it spits out the best answer it has found.

    Rules: You MUST specify a tolerance zone at least as big as the radius of your ruby. In practice it seems that you must go a bit bigger, ~.005", or it will occasionally throw a best fit error message and give you some crazy results.

    How well does it work? : At first it works great. It generally improved my profile numbers by ~.001-.002 in an .008 zone. In my opinion that is a very significant improvement.

    So what's the catch? : Only that it slowly and quietly chews away at the integrity of your programs' nominals and eventually something breaks and your program falls apart in a sudden and catastrophic failure. Other than that its great!

    Unsolicited advice: DO NOT turn this on in your master production program. If you do, make sure you have a very good collection of backups (I did, luckily). If you want to use this add in one of the auto save-as scripts that are in the code samples forum so you have a copy of each part inspection. Then, after making a backup, turn this feature on in the saved off file that contains your actual inspection data and it will run the iteration and, very likely, give you a better number for your profile dimension. This way it only gets run once and won't continuously overwrite the nominals in your master program.

    Also, probably best to check with your customer before providing data created with this feature. It is unclear to me whether this feature is truly compliant with the ASME standard.

    Hope this is helpful to someone.
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  • Ok, I'm going to answer my own question here based on some experimentation and give myself, and anyone else who might come along later, some advice:

    What does it do?: It seems to work like a mini iterative alignment for your profile dimension. It will take your measured points and move them around on the CAD model within the tolerance zone you allow. It moves, pierces, iterates, re-pierces, and reiterates until it hits your maximum allowed iterations. Then it spits out the best answer it has found.

    Rules: You MUST specify a tolerance zone at least as big as the radius of your ruby. In practice it seems that you must go a bit bigger, ~.005", or it will occasionally throw a best fit error message and give you some crazy results.

    How well does it work? : At first it works great. It generally improved my profile numbers by ~.001-.002 in an .008 zone. In my opinion that is a very significant improvement.

    So what's the catch? : Only that it slowly and quietly chews away at the integrity of your programs' nominals and eventually something breaks and your program falls apart in a sudden and catastrophic failure. Other than that its great!

    Unsolicited advice: DO NOT turn this on in your master production program. If you do, make sure you have a very good collection of backups (I did, luckily). If you want to use this add in one of the auto save-as scripts that are in the code samples forum so you have a copy of each part inspection. Then, after making a backup, turn this feature on in the saved off file that contains your actual inspection data and it will run the iteration and, very likely, give you a better number for your profile dimension. This way it only gets run once and won't continuously overwrite the nominals in your master program.

    Also, probably best to check with your customer before providing data created with this feature. It is unclear to me whether this feature is truly compliant with the ASME standard.

    Hope this is helpful to someone.
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