Why you should avoid monuments with dowel pin holes instead of 3 point contact
We have noticed that some of our customers are still using monuments with dowel pin holes in them instead of a 3 point nest. We strongly recommend against this practice! Why?
- Some of these monuments are in “cup” configuration, meaning that debris falls to the bottom of the cup which you must try to wipe clear somehow. Did you get all the chips out? Hard to see. Hard to know if you were successful.
- Dowel monuments mean you are now carrying around handfuls of nests to insert into the monuments.
- When you insert a nest it can sometimes “piston” and lift up your nest slightly, giving you a bit of error.
- Some of the cup monuments have inadequate clearance so you can’t get your fingers around your nest to pull it out…so you need a tool to pull your nest free. Time consuming.
- Under the best circumstances you are adding a nest (with a tolerance) to a monument (with a tolerance). Eliminate one of those stacks by going to a 3-point nest design.
There are plenty of negatives for the dowel pin style monument…and we can’t think of a single upside. Don’t use them!
How many monuments do I need and how do I lay them out?
All other things being equal, we like to throw down a 10’ square grid. This is denser than you will generally need for most applications,
but typically most points will not be visible from any given setup and you will be glad of a good selection of points.
We usually do LOS (line of sight) checks in CAD to critical tracker locations. Very often something gets added to the system after the
fact blocking LOS to certain points, so we need to add another point or two later. Choosing a sensible naming scheme makes this easier
(consult us for advice on this).
Metrology Software
- Polyworks
- Spatial Analyzer
- Verisurf
- Operation Commander (Task Execution Software)