GRID DIGITIZING TIPS
Digitizing is, by its nature, a slow, precise process. The time it takes to digitize a part is effected by
four factors: feedrate, step size, detail density and over-all shape of the object.
The feedrate settings in parameters 14 and 15, (the fast and slow probing rates). As a general rule of
thumb parameter 14 should be set to 20 or 30ipm for digitizing and probing. This setting will not affect
the accuracy of the digitizing data, but will speed up the approach cycles during the digitizing run and
there by reduce the time the run takes. Parameter 15 however does have a direct effect on the accuracy
of the digitizing data and should be adjusted to match the tolerances you are calling out for the finished
part. Typically setting this parameter slower will yield more accuracy and faster less accuracy.
The accuracy achieved on vertical surfaces is also dependent on stylus length and related PTV (pre-
travel variation) for the probe being used. If vertical surface accuracy greater than the PTV value is
needed then a probe with appropriate PTV is required such as the DP-7.
If your part does not require very close tolerances then adjusting these probing rates could save you a
significant amount of time, but if you set the feedrate too high the results you get may not meet your
requirements and you will just be wasting time. So start off cautiously, it is better to take a little longer
when you are first starting out. Once you have several digitizing runs under your belt, you will have a
much better feel for where these parameters need to be set to achieve the results to meet your job
requirements.
The X, Y, and Z stepover – The smaller the stepover distance, the longer the digitizing run. For
instance the typical time it takes to digitize a 1” by 1” grid with a step over of .010” in X, and .010” in
Y, (with parameters 14 and 15 set to 30ipm and 5ipm respectively), is 45 minutes with 10,000 data
points being recorded. By changing the X stepover to 0.005” and the Y stepover to 0.005” the time
increases to 3 hours with the number of data points recorded increasing to 40,000. The trade off with
time, is surface finish and detail. The finer the stepover amount in the digitizing run the better the
surface finish is going to be in the final part and the more fine detail you will be able to capture. As the
end user, it is up to you to find the settings that give you the finish, and detail level you are looking for
in the final part.
Remember, the Centroid control can digitize unattended, 24 hours a day, 7 days a week, if you really
need the detail and finish, (just remember to fill the automatic oiler tank!).
The third factor that affects the time it takes to digitize a part is the density and height of the surface
detail. The more vertical walls the probe stylus must climb, up and down over, the longer the digitizing
will take. This is not a factor you have much control over, except for adjusting your Z stepup distance,
but in general this will have little effect.
Finally, if the piece is odd shaped, you may want to patch several small digitizing runs together and
there by eliminate the wasted time that would be spent moving over areas that are not pertinent to the
data you want to collect.
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