I have been chasing scanning work at Stennis Space Center here in Mississippi for some time now. There is lots of work being done to the old test stands and I have been trying to educate several of the private contractors who have that work as to the advantages of laser scanning for those structures. I'm making a little progress in that we will be allowed to come in behind another surveying firm to scan two rails that will be installed on the 7th level of one of the old stands. The rails will be for some kind of moving platform. The other firm will be surveying it conventionally and the contractor wants to compare time, cost, deliverables, etc. An engineer just informed me that the government specs for the rail tolerances were 0.0008'. I told him that was way out of my league and that I didn't see how anyone could measure anything that tight especially 7 floors up on a steel girder structure. I need to be educated on this type of surveying. Do any of you guys do commercial measurements with very tight tolerances? And if so, what instruments and/or procedures do you use and what is the upper limit of the tolerances you can certify?
Thanks
I would first make sure that the engineer wasn't pulling numbers out of thin air. Does this engineer work for the company you're going in behind? Is he trying to scare you off? Not make his company look bad?
I don't know of any survey grade equipment that can measure to that tolerance. I don't gap my spark plugs that precise.
4x greater than 1 mm accuracy?:-S
and of course, they couldn't even build it that close.
> 4x greater than 1 mm accuracy?:-S
In a controlled environment, a properly calibrated laser tracker will repeat measurements to 0.015mm
That is getting into another side of surveying, precision machine alignment.
It is similar to blue printing an engine with the micrometers and dial tolerance meters.
0.02
Sounds like a specification that was pulled out of something completely unrelated and used because "it sounded pretty good." I have run into that a number of times, and it takes some diplomacy to get the Specifying Engineer onto the right track.
> An engineer just informed me that the government specs for the rail tolerances were 0.0008'.
That's metrology, not surveying. There are people who specialize in this sort of ultra high precision work. Its for laying out, setting up, and aligning industrial equipment.
.0008m = .003':-S
But that still seems kinda tight.
> An engineer just informed me that the government specs for the rail tolerances were 0.0008'.
LOL!!!
Stennis Space Center is a very large government facility with multi-agency and private industry within it’s boundary.
A lot of action is NASA because that is where they conduct the tests for rocket engines. Huge buffer zone area surrounds the site and when they do a test, it is bigger than the 4th of July for excitement. There is a myth that when a Saturn rocket fires that a women who is watching close by can have a orgasm. :-X
SSC was created by LBJ for his senatorial ally from MS…John C. Stennis.
The management is contracted out to one of the few mega- engineering entities in the US and they change hats of the contractor for Stennis Space Services every 4 years or so. Employees usually rollover to the new management and continue their work. All the big boys have been there and revolve. I think Jacobs may be there now.
A very good friend of mine has been the structural C.E. for the test stands for 20 years or so. Before that he worked at the Savannah River Site in Aiken, SC on the containment structures for radioactive waste. He commutes from New Orleans. He has been trying to retire for the last few years but they offer him employment packages that he can’t refuse. BTW, he is a former student of Prof. Clif when he was at UNO in the early 8o’s 😉
I have done some sub-contracting for another firm for site surveys through the years. I have tried to get on the contractor list but the contracting process was a real mess created by the paper shufflers so I finally gave it up.
About 2 years ago, I was asked to consult about locating anchor bolts on an old test stand that was being refurbished. I did suggest that laser scanning was in their near future for this work. I told them that I was not able to accomplish the criteria that they wanted the survey to be performed but I could get them close. I am only comfortable doing site plan topos out there. Most of the in-house survey folk are engineers who rely on the kindness of survey contractors some of which are low ballers, I might add…
since it is government work. There is a lot going on out there. Rolls Royce and other private space rocket firms do their tests out there. NOAA has a big presence out there with the Natl. Buoy Center. A lot of research university and private firms are there and the Navy Seals use it for survival training because it is surrounded by the Honey Island Swamp which is very severe swamp terrain. If you want to be a Seal, you are going to spend a lot of time in the swamp there with the gators, snakes and bugs chewing on you.
Alan,
Maybe we should get together for that lunch in Slidell.
I suggest...
http://www.lapinescafe.com/Weekly%20Lunch%20Specials/wls.htm
A former coworker has spent years as an engineer on various corps construction projects. He told me of one project where they were using a laser level, and some paper pusher came out and shut the project down. She had read in the safety specs about the procedures and precautions when using lasers and saw that none of that was in place for this project.
I can believe the tolerance on the rails was .0008. My bet is that was their 'machine part' tolerance during their manufacture.
I can also believe an engineer with a government job letting the clutch out on his mouth before he put his brain in gear.
Not merely a biased opinion, mind you. Just a factual observation over a period of time as a government employee.
Right on, Paden.
Had some similar conversations with Engineers with General Dynamics on a project a few years ago. They sometimes don't see the various tolerances along stages of a project. Since the parabolic surface of the 10 meter dish antenna has to be built to a tolerance of a couple of thousandths, therefore the dirt work under the antenna needs to be to the same specification.
A telecommunications company had a specification for a alignment line 10ft long to the hundredth of a second. I don't sign any contract that has unattainable specs.
No pun intended, right?
Wonder what their tolerances for construction were? .0008'... whose going to prove you wrong?
Robert, I will give you a call soon. I am going to lunch with the engineer I have been talking to out there on Friday so after than I could fill you in on it better. The engineer is a good guy and was reading to me right off the specifications. After looking at that Faro Laser Tracker, I have to admit that it's pretty cool stuff and theoretically could meet their standards. I don't believe it myself but hey.... I'm a cynical old surveyor. I did manage to meet CH2M Hill's criteria to be a survey vendor out there and we completed a topo around the control building for Test Stand B. Their vendor application once filled out was close to 140 pages.
Thanks for the responses. After looking at Laser Trackers it would seem that the specifications for the equipment meets or exceeds their criteria. I don't believe they can build it that close but... what can we say.
There is a guy that used to post here frequently that does this type of Industrial Surveying/Metrology. Falk PLI