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Find out Tolerance used for step file

Creator
Creator

Hello,

 

when I imported a step file to NX, is it possible to find out the tolerance value which has been used for creating the step file?

Or can I see it from the step file itself, without using NX?

 

As the standard value in our Environment for NX11 is some inch value, which is not supposed to be used, I want to make sure that the step files which are created have the correct tolerance setting.

 

Thanks,

Ralph

11 REPLIES

Re: Find out Tolerance used for step file

Genius
Genius

as I remember, it should be    UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(xxx), ...

within the STEP file

 


 

As the standard value in our Environment for NX11 is some inch value


You mean that your precision is some inch ?   =8-|

Re: Find out Tolerance used for step file

Creator
Creator

Excellent, thank you very much!

Re: Find out Tolerance used for step file

Creator
Creator

Actually I just found out, that in a step file I just exported from NX11 I have several entries with different tolerance values, although I entered 0.01mm for B-apline Tolerance:

#70412=UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(0.1),#70421,
'DISTANCE_ACCURACY_VALUE','Maximum Tolerance applied to model');
#70413=UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(0.1),#70421,
'DISTANCE_ACCURACY_VALUE','Maximum Tolerance applied to model');
#70414=UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(0.0455226515310176),
#70421,'DISTANCE_ACCURACY_VALUE','Maximum Tolerance applied to model');
#70415=UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(2.E-5),#70421,
'DISTANCE_ACCURACY_VALUE','Maximum Tolerance applied to model');

 

That means NX is not using the value from the field B-spline Tolerance for all features but choosing a random tolerance value?

How can I make sure, that the exported step file has the quality I want?

 

Thanks,

Ralph

Re: Find out Tolerance used for step file

Genius
Genius

I suppose this is the max. edge tolerance of your model.

Try Examine Geometry and check this value.

 

As for the 0.1, as I remember this is the max. range of the UNCERTAINTY_MEASURE_WITH_UNIT field

for exported model, which means that your edge tolerance in these models could be

higher.  If this is the case , this is a problem, and  you may want to check this with Examine Geometry.

 

Re: Find out Tolerance used for step file

Creator
Creator

I checked the maximum edge tolerance in my model with examine geometry and the maximum value is 0.0105mm, but the UNCERTAINTY_MEASURE_WITH_UNIT value in the step file says 0.0222979980665933mm.

 

I don't understand that.

Re: Find out Tolerance used for step file

Genius
Genius

if you can post your model we can have a look (and if you post a NX9 Parasolid users with NX9 like me can have a look as well)

 

 

Re: Find out Tolerance used for step file

Creator
Creator

Unfortunately I cannot provide the model, but I don't see that this is a model issue anyway.

 

When I can set a tolerance / accuracy when creating the step file, I expect the system that this is used and not a different random value. Otherwise I do not understand what this tolerance setting is for.

Re: Find out Tolerance used for step file

Genius
Genius

the B-spline Tolerance is just for refitting NX surfaces/curve that don't have a STEP equivalent (e.g. NX blend).

If you modeled your part with a loose tolerance you shouldn't expect NX to make it more precise, nor you

should want to, as NX (or whatever software) cannot know what you want exactly.

 

I checked the STEP format, and UNCERTAINTY_MEASURE_WITH_UNIT is defined as the "model closure tolerance",

that is the largest gap in your model.

If you managed to sew surfaces into a solid, that should be the gap prior sewing.  When you sew surfaces and there

is a gap, NX enlarges the edge tolerance of the first selected edge to touch the second edge, so I expect the

max. edge tolerance to be basically the same as the max. gap, but maybe this is not always the case.

This why it would be interesting to see even a small portion of your model, just the one which is more problematic for you.

Re: Find out Tolerance used for step file

Creator
Creator

Ok, thank you very much for your explanations.

 

My intention is, that the step files which are generated shall have a certain quality, e.g. a distance tolerance no larger than 0.01mm. This is our standard setting for all models. But apparently there is no option to influence the quality of a step file, besides the b-spline tolerance, which influences just a part of the model.

 

Thanks.