From: Philip Hewitt (
Date: Fri Mar 03 2000 - 18:53:08 EET


Further to your question about surface inspection, I can perhaps give you
some insight.

I work for Delcam PLC in the UK ( and we produce CAD/CAM and
inspection software. Our inspection package is called PowerINSPECT
( and it is designed to inspect free surfaces.

There is no simple answer to your question of 'what should be inspected?'
It is always important to bear in mind why you are inspecting the part.
Features of the part which must fit with other parts (e.g. location holes or
mounting lugs) must be examined more closely than featureless surfaces.

Inspection of this type is normally carried out on a co-ordinate measuring
machine. The University of Missouri-Rolla has a good brief introduction to
co-ordinate measuring machines at

The hardware can be divided into different categories. Co-ordinate
measuring machines are usually separated into CMMs as shown in the
presentation above, and articulating arms such as those made by Romer Inc
and Romer France (,

There are also other types of measuring machine and there is an excellent
introduction to these by a guy called Dimitri Papadopoulos at

The inspection hardware outputs co-ordinate and other data, and you need
software such as Delcam's PowerINSPECT to do something useful with this.
Normally the inspection software is on a PC which is connected to the
measuring machine either through a dedicated PC expansion card connection or
a serial port.

A very brief description of PowerINSPECT is as follows:

You get CAD data for the part as well as the physical part itself.
You align the physical part to the CAD data by probing a few points on the
part. The alignment may be produced in different ways- either by measuring
known features on the part, or by a free form fit.
Then you start inspecting the part for conformance to the CAD.

Among the features that we can measure are:

Geometric items (e.g. plane, cone, slot)
Surface inspection (points on the part surface are probed and compared with
the CAD- either there is too much material, or too little)
Edge inspection (similar to surface inspection- points along an edge are
measured for conformance to the CAD)

All of the measurements can be shown graphically on the screen, and have an
information sheet associated with them (e.g. a measured circle will be shown
on the screen against the CAD where it was measured; a separate tab allows
you to see the co-ordinates of the centre, the plane in which it was
measured, tolerances used, and the actual points probed). This information
can then be reported in a number of ways.

The point of inspection software such as ours is to make the whole process
of surface inspection as quick and easy as possible- particularly for
occasional users who do not use inspection equipment full time. If you are
not familiar with these products I suggest that you have a quick look at our

I hope that this is a helpful general answer to your question. I would not
like to give a more specific answer without knowing a bit more about what
you are trying to measure and why. Feel free to contact me if you have
further questions.


Philip Hewitt

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