Appendix C Elevation Studies & 3-D Dipstick Topo Maps
C-1
1. Why do it?
The Dipstick
will enable you to collect elevation data that is much more precise than that available from a Rod and
Level. If you need to know exactly how a surface looks in 3-D, or if you need very precise elevations of points on the
surface, you can make a 3-D elevation study on your own. Some examples of reasons for doing an elevation study
include:
checking drainage patterns, such as checking for "birdbaths" where water might collect on a nominally flat
surface;
determining exact elevations of critical locations such as mounting pads for a machine that must be mounted
exactly level;
determining exact elevations for a system that interfaces with the surface;
checking the results of corrective grinding, and other reasons.
2. What is the Difference between an Elevation Study and a 3-D Map?
A 3-D Map requires much more data than an Elevation Study. That's the fundamental difference. For an Elevation
Study, you can collect a limited amount of data, and you can collect it where you need the data. To make a 3-D Map,
you need to collect the data at regular intervals over the entire surface of interest.
3. What Do You Need?
To make an Elevation Study of a surface, all you will need for a basic study is your Dipstick
. This will
allow you to graph lines (one at a time or many at once) and calculate elevations of each of the points on any of
the lines.
To make a 3-D plot of a surface, you will also need a 3-D plotting or graphing software program such as
Microsoft Excel
or Perspective Jr.
or a specialized graphing program like Harvard Graphics
. These
programs take the data and present it as a 3-D plot. What you need to do to make this work will be explained
below. We'll demonstrate how to do it in MS Excel
, which most people have access to.
Whichever method you want to use, you need to decide the data location and spacing before you start collecting data.
4. Dirt or Grit on the Surface
If the surface is excessively dirty, have it swept to remove the dirt/grit that you would otherwise walk over. (A light coat
of dust is OK, but not piles of dirt or grit.) This can be important, depending on the desired accuracy of the result,
because the Dipstick
can measure to .001 inch, or 1/10 mm. The cleaner the surface, the better your data will be.
When you compute the Surface Roughness Bias from the data you collect, check to ensure that it is less than .002"/step.
Anything more indicates a problem.
3. Marking the surface
You need to collect the data in lines that are precisely located. You should mark straight lines so you won't wander
around while collecting data. There isn't any point in collecting very accurate data that isn't in a regular grid, because
the graphing program will place it in a regular grid. Starting at a convenient point near one corner of the surface to be
measured, mark this starting point with chalk, crayon, or a dot of paint. Lay out the lines where you will collect data,
spacing the lines evenly if you are doing a 3-D Map.
Paint is much better than chalk or crayon, if you need a permanent reference, because when you get the results calculated
and graphed, you will be able to go right to the key spots on the surface. As a minimum, mark the 4 corners of the area
to be measured. It's best to also mark the measurement lines with a chalk line or similar method. We like to spray paint
clear lacquer over the chalk line so it will last for a while, but a temporary method is OK, so long as you can find these
lines later from the paint spots at the corners.
5. Three Ways to Collect Data
You should collect the data in closed loops, in any of these three methods:
"Out-and-back" lines
A "Comb" pattern, or
A series of "boxes," either overlapping, or tied together by one or more "base" lines.
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