Re: digitizing

From: Steve_Farentinos (
Date: Tue Jun 04 1996 - 15:25:37 EEST

Pierre Bertrand wrote:
> Have you had experience with both CMM and lasers? How did time and costs compare? Were
> there more problems with creating the model with either? We are considering buying a
> laser and are not currently using a CMM.
> Pierre Bertrand
> Kaiplast Inc.
> Montreal


We have been using CMM's and occasionally lasers for digitizing/reverse engineering for
about 10 years. I can easily say that for most parts I would choose the CMM. Here are
the pros and cons of each as I see it:

The CMM is better because:
1) the CMM is very good at setting up part coordinate systems according to a datum
structure. This allows you to easily digitize in stages, i.e., move or turn the part and
re-establish the previous coordinate system.

2) The CMM is more accurate than the laser

3) The CMM can acquire point data and measure features on top, on the side and even
underneath a part.

4) The CMM can measure features of position and form in the same set-up as the digitizing
is done. For example, you might want to digitize a contoured surface then measure the
position os several mounting bosses on that surface. It is far more useful to get exact
numbers for the size and location of these bosses than it is to have a number of points on

5) The CMM allows you to control the point density during digitizing: more points in
convoluted areas and fewer in flatter areas. An obviously planar area can be digitized
with exactly three points.

6) Since the CMM can measure size and location of primitives, it is better suited to
working with feature-based solid modelers.

The Laser is better because:
1) the laser can digitize hundreds of times faster. This is very useful for creating
surface models of parts that must be built as "free form" surfaces (for example, a human
hand). If this is the type of work you're doing, I highly recommend a good software tool
for dealing with the thousands of points the laser will provide.

2) The laser provides point data that are ON the surface of the part being digitized.
This is not the case with the CMM, where the points represent the center of the ball
stylus and a later offset operation has to be performed to compensate. This is like
creating the cutter path for a ball-end mill, but in reverse.

3) Some laser systems can go directly to an STL file after digitizing a part.

As you can see, you choice depends on the type of parts you will be digitizing.

I hope this helps.


Steve Farentinos
PML, Inc.
201 W. Beach Ave.
Inglewood, CA  90302
310 671-4345
310 671-0858 Fax
310 671-1862 BBS

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