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NX4 Sketcher: How to control "Arc Length"?

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tooldeziner

tooldeziner

Aerospace
Oct 14, 2005
98
Looking through the available functions, it appears that the closest thing to Arc Length dimensional constraint is Perimeter. However, when I set the Perimeter value to 40mm, for instance, then measure the actual length of the resulting arc using "Analysis > Arc Length", the length is 13.33mm.
1. What does the Perimeter constraint actually do?
2. How can I control an arc length in sketcher?

Thanks,
'ziner
 
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It seems to work OK for me (I'm running UGS NX 4.0.4.2). One thing that you need to be careful of is that the 'Perimeter' constraint can be applied to a string of curves as well as just one. Make sure that when you applied the Perimeter constraint that you didn't select more curves than just the single arc.


John R. Baker, P.E.
Product 'Evangelist'
UGS NX Product Line
SIEMENS
UGS PLM Software
Cypress, CA
 
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As far as I know, it does relate to the curve length. Perimeter "should" work, it does in NX3 (kind of) and NX5. That obviously doesn't guarantee it works in NX4 however. Unfortunately I don't have NX4 (at the moment) to test.

Specialty Engineered Automation
 
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Thanks for your interest, guys.
Here is what I am doing:
The goal is to drive a sweep along an arc, controlling the arc length using an expression "S".
The geometry for the sweep extrusion and the arc is in separate sketches. The arc sketch was created solely for this purpose, no other geometry in there to cause conflict. The sweep is a trianglular shape, only 3 lines in the sketch, with one corner anchored coincident with the start point of the arc. The sketch plane of the sweep geometry is normal to the sketch plane of the arc. In the arc sketch I applied the Perimeter constraint. (Is it typical for that constraint not to show anywhere except in the "Tools > Expressions" list? Can't see it in the sketch.) I also added constraints to anchor the arc center and the start point, and a radius dimension on the arc. Fully constrained.
In the Expressions list, I created an expression "S", for arc length. The value of S is 20mm. Still in the expressions list, I edited the p value for Perimeter to become "p=S". The extrusion changed immediately. Eureka! I thought. However, when I analyze the actual length of the edge of the arc (Analysis > arc length) it is 6.66mm. This is the same length as the edge of the sweep that was driven by the arc. When I change the expression "S" to 40mm, both the arc sketch and the sweep update to reflect the change, but the true length is 13.33. I'm confused.
If you got this far, thanks again for your interest.
'ziner
 
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The arc radius is 28mm. I have also tried starting a new sketch for the arc, same result.
As for the constraint value of the Perimeter, I can't see any reference to the value or even the existence of the constraint while in the sketch. It doesn't appear in "Show/Remove Constraints". I have to leave the sketch altogether and go to "Tools>Expression" to see it. That could be very perplexing to anyone else trying to edit my sketch at a later date.

Thanks,
'ziner
 
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Actually, just select the 'Inferred Dimensions' icon and then the 'Sketch Dimensions Dialog' option and you will see all the dimensional constraints in the sketch including the perimeter constraints.

Note that I tried, from your description and values, recreating your sketch with the single arc and everything works OK for me. How are you measuring the length of the arc? Are you using Analysis -> Arc length...?


John R. Baker, P.E.
Product 'Evangelist'
UGS NX Product Line
SIEMENS
UGS PLM Software
Cypress, CA
 
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NX 4.0.4.2 was made available for download from GTAC on 17MAY07.

Tim Flater
Senior Designer
Enkei America, Inc.

Some people are like slinkies....they don't really have a purpose, but they still bring a smile to your face when you push them down the stairs.
 
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I think the version is NX 4.0.3. How can I confirm that?
Thanks,
'ziner
 
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I opened a new file and recreated the sketch, and it is ok. So I will just dump this one and say "oh well".

'ziner
 
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