Class A surface - Deviation limit

[mahtab_msa]

This question is not directly related to Pro Engineer but I think people using Pro E REX can help.

I need to know how much deviation is acceptable to create Class A surfaces for automobiles. I have read threads about Class A surface or G2 continuity, and I think I understand what it is. But Can some body provide some references/examples of deviation limits when creating surfaces from point cloud data, especially for automobiles.

I have recently got a job in a design firm and I am getting training on using ICEM surf to create Class A surfaces from point cloud data/data from 3D scanners. I have practiced on a model to achieve deviation within limit of 0.3 mm. I read in a thread that deviation of 0.1 mm is achieved to model mouse from point cloud data (james lynch said that, he works on similar stuff .. let me PM him

) .

 

[[-Skint-]]

0.1mm... jeez, the paint finish is probably 0.5mm and covers all the errors

 

[mahtab_msa]

well I am looking for some kind of standards in automotive sector ... i.e. what is the usual deviation limit ... and I have to tell my boss

.

 

[james.lynch]

]0.1mm... jeez, the paint finish is probably 0.5mm and covers all the errors

I wish!

I would hope that the paint would be consistant and essentially only offset all the errors! anyway - the paint thickness is actually between 15-50 microns (depending on how many layer paint it is).


As for the tol on matching scan data - well it depends on teh quality of the model in our case - if the model is right then generally -we can match most fo the surfacesto within 0.1mm (not REX surface). But often we do come off the scan data in areas -0.2, 0.3 or sometimes more.. but this deviation is ALWAYS done in colaboration with the designer.


I don't know what the tols are for the automotive industry unfortunately - but I would love to know!


Keep us posted!


James

 

[mahtab_msa]

well i cant find such info on internet

. I will post here when i get some information. Thanks for the info

 

[[-Skint-]]

Two friends of mine work for car companies, one Jaguar and the other Honda. I will drop them both an email to see if they can answer this question.Not promising anything, but watch this space.


mahtab, how quickly do you need the info ?

 

[design-engine]

you can't do a class surfaces in REX. Don't even try.

Any divination is not acceptable to meet A-Class surface.
Edited by: design-engine

 

[mahtab_msa]

Skint, let me know if you get some information. I will be getting class A surfacing training in ICEM surf soon, so any info before that will be helpful.

Bart, the deviation is not in terms of surface quality. It is between the original point cloud data/mesh and surface that is created. i.e when you compare surfaces with original data, you need to keep the surface within certain limits.

thanks everyone for reply.

 

[jeff4136]

[url]http://aliasdesign.autodesk.com/learning/tutorials/details/B uilding%20a%20Sportscar%20Exterior%20To%20Class-A%20surfacin g%20Standards%20Part%203_133095/ [/url]


The page isn't currently loading correctly for me but the text is coming up...


5.4 Evaluating the rebuild tolerance
"A common tolerance to rebuild a full scale size clay model of good quality is 0.25 mm."


... there's a little more discussion so read thru it.

 

[mahtab_msa]

hey Jeff

thanks a lot for the link

. Its loading properly here and I am reading it right now.

 

[mahtab_msa]

<h4>According to this document (section
5.4 Evaluating the rebuild tolerance), if point cloud data is obtained by
scanning a clay model, then a common deviation/tolerance range to achieve class
A quality surface for automobiles is 0.25 mm.
</h4><h4>This value is for a good quality
clay model. This tolerance value depends on the accuracy of clay model (or any
other model used to get scan), and client requirements.</h4>James pointed out the same thing that it depends on the quality of the model

thanks Jeff


<h4>
</h4>

 

[acad]

you can't do a class surfaces in REX. Don't even try.



Any divination is not acceptable to meet A-Class surface.

Could you explain please ?

Thank you

 

[design-engine]

The definition of an A-Class surface means it has no deviation.I could and probably already have defined A-Class surfacing on this board someplace. A-Class surfacing is about light reflections being very specific with certain continuities.

So when you ask rhetorical question "how much deviation is allowed to make for an a class surface". Anyone have an analogy.

Now if you use a point cloud data to rebuild a surface using non Bézier curves and surfaces then you are not talking about how far your new geometry veers from the point cloud data. Thats a different kind of deviation.
Edited by: design-engine