RE: little bit off topic (about inspection)

From: Tommy Tucker (
Date: Mon Mar 20 2000 - 19:44:23 EET


I thought your question was very interesting and was surprised not to see
more discussion. Scanners and three-dimensional measurement equipment have
been discussed a lot on this list, but this is a subject that rarely comes
up. Everyone thinks its great to inspect free-form shapes but doesn't say a
whole lot about what they mean by it.

The main advantage in free-form surface inspection using scanning/digitizing
technology has been the use of color mapping the errors from measured points
to CAD surfaces. You raise an interesting question as to whether this is
enough. Most of the other features you mentioned require a tolerance.
Free-form surfaces should to, but how are these spec'd out? Any input from
others on the list would be appreciated. My company is in a position to
provide real innovation in this area based on input received.

One area I have seen a tolerance used for free-form surfaces is turbine
blades. Generally, these are spec'd out by cross-sections along the blade's
length. This has always bothered me because it takes a 3D geometry and
simplifies it to 2D. With modern modeling systems, why can't a 3D
tolerancing scheme be imposed? In any event, you may want to look into
turbine blade inspection and how inspection planning is performed for these

Tommy Tucker
(vc) 408-855-4372
(fx) 408-855-4360

> -----Original Message-----
> From: []On Behalf
> Of Steve Pitt
> Sent: Friday, March 03, 2000 3:23 AM
> To:
> Subject: little bit off topic (about inspection)
> Hello List,
> I am Ph. D. student and my research topic is about inspection planning.
> I have a question about inspection.
> For inspection of freeform surface, what should be inspected?
> There exist a lot of inspection features such as plane, cylinder, etc.
> In that case, sampling several points is enough.
> But I think that freeform surfaces are different from the features.
> Just is it enough to see the difference between point data and
> the original
> surface?
> Or the surface which is reconstructed from point data must be
> compared with
> the original one?
> Which way is a CMM used for inspecting freeform surface?
> I respect the answer from anyone who has expriences for freeform surface
> inspection.
> Tnank you in advance.
> Steve Pitt
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