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2oldfarts (the rockhounders)

Unusual Marks On A Disk

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We found this benchmark A 51 near Moapa, Nv. It is a standard bronze disk but it has 'dimples' on the face of it. We are curious as to what purpose these would serve. Here is a picture of the disk.

 

74172_100.jpg

 

We thought the 'dimples' would be considered defacing the disk. Any opinions would be appreciated.

 

Thank you John & Shirley

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It looks to me like someone whacked it a few times with a ball-peen hammer. Dimples like that would serve no purpose in surveying that I'm aware of.

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I worked summers for a surveyor years ago. Those marks you saw could have been from the plumb-bob older surveyors used to center their instruments over the benchmark. they needed to get it real close and sometimes the heavy'bobs' would slip and drop , creating what youy saw in the soft metal marker. Hope this helps answer your question.

 

Lafrog

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I'll have to second the ball peen hammer theory. There is no plumb bob that I now of that would make a mark that blunt or deep.. The biggest plumb bob I've evr used in 25 years is 36oz and a brass disk is a bit sturdier than that. Also for the record instruments are almost never set over a benchmark only level rods go on BMs, instruments are placed over horizontal control stations. I say almost never because I'm sure someone will say that they extended vertical control via trig using a theodolite.

 

Cheers.

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I vote for 'shots fired'. It looks like what a .22 caliber or similar sized, fairly low-powered round would do to a disk. I've seen several around my neck of the woods that have been shot and exhibit similar marks.

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Plumb bobs have a very precise pointed tip. On most of them, the tips are replaceable and made of a soft non-ferrous alloy - softer than a brasscap anyway. Unless the plumb bob was dropped from a few hundred feet, it would do little to no damage to the mark.

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I have found several with the same type markings.

 

I thought(Assumed) that it was marked (by Surveyors),the Exact point of their plumb bob,after the completion of the work.

 

And I have read that the Station is occupied during the Survey,not another spot,that is where the rodman comes in.

 

The book says for: Triangulation Stations,that is ,where the instrument is set up to measure angles of the main system.

In most Triangulation systems,secondary control is established by observation to stations in the vicinity of the Major Station,but these secondary statons,called minor stations,are not used in the extension of the main system of triangles.

 

In the work of ordinary precision,the average error of closure of the Triangles should not exceed 5"

 

The Instrument is set up at each Major Station

 

In addition to the monuments for Horizontal control,a system of Benchmarks for vertical control has been established throughout the Country.

 

To make use of the State System for a local survey,the surveyor set up his transit at a nearby STATION of the Triangulation System,orients it on the line of known plane azimuth,and runs the survey(by traversing or triangulation) the area under consideration.

 

The coordinates of any point in the local survey can then be conveniently computed in terms of the State System by the ordinary methods of plane surveying

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Not a gunshot or center punch, looks to be random impacts from a tool such as a welders' slag hammer. Could some one have broken ice from the surface? Not a ball peen hammer, craterization to small.

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Just a little observation, if anyone's noticed, the benchmarking page's logo has a picture of a benchmark with these same dimples.

 

surveymarker.jpg

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Hail storm??

 

Or could be from having a bunch of the disks in a pail. They often get mared up just riding in the truck for years, the metal is soft.

 

Here is another, this one along the shore of Lake Superior

 

AC6018_909_9039_E-3.JPG

 

And here is another with a lot of marks (its in area where cars park)

TY7767_WEST_BLUFF_2-3.JPG

Edited by elcamino

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Refering to the original post:

Not plumb bob,

Not hammer, neither ball peen or rock,

Not bullets

Not hail.

 

The dimples were made with a round punch (sorry damfyno). I've seen and made enough of them in my long ago surveying days.

 

I've just never been able to figure out why anyone ever made one, let alone multiple, dimples in a USCGS benchmark.

 

It was set as a benchmark (elevation reference), not as a horizontal control monument, though it could have been used later for that purpose. The comical thing is that it may never have been offically used by the for anything, as it never had the measured elevation stamped on it, was effectively destroyed and moved at some indeterminate time, and has not been recovered since 1941.

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Well I think I found the answer to the marks in the New book I just got.

 

Manual Of Triangulation page 87.

Case IV.-The Station mark only is moved.

If the station is to be moved,it is generaly practicable to establish a new mark in the new locaction,and when is done the old mark is completely destroyed.

 

it goes on and then states

if the old mark and disc are to be re-used,the original date shall be effaced by light tapping with the rounded end of a ball-peen hammer and the disc restamped with the new year.

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Yea I went back and looked again too...The one with the initials drilled in it looks more like it has ben peened,then some one drilled their initials.

 

If we ever come across one now we will know in some cases when re-set it was peened.

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Blindleader, I was making the same assumption you were. But the original link to A51 really goes to I1. If you find A51, last logged in 1982, you will agree that the stamping is correct, the elevation (GPS) is only off 8+ feet and the coordinates (GPS) are +/- 1 second. I too have seen many dimples like these but never think about their origin. My 16oz PB wouldn't begin to make a dimple (a steeper pin hole maybe).

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Well I think I found the answer to the marks in the New book I just got.

 

Manual Of Triangulation page 87.

Case IV.-The Station mark only is moved.

If the station is to be moved,it is generaly practicable to establish a new mark in the new locaction,and when is done the old mark is completely destroyed.

 

it goes on and then states

if the old mark and disc are to be re-used,the original date shall be effaced by light tapping with the rounded end of a ball-peen hammer and the disc restamped with the new year.

I think I located a picture of the type of marking you refer to.

 

64381_400.jpg

 

PID# is FZ1197.

 

Thanks for your input.

 

John

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Thanks for the picture I have found some myself but can not remember which one out of the several 100, I have to go back through.

 

I will keep better track on unusual marks found on a disc.

 

I did not even know that until I started reading the Manual.That is there were some that were reset and peened.

 

The one in particular I remember after peening the disc, it is almost flat looking with lotsa dimmples.

I could really tell something was diffrent..................Hey I think I remember will get back to yall.

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Blindleader, I was making the same assumption you were. But the original link to A51 really goes to I1. If you find A51, last logged in 1982, you will agree that the stamping is correct, the elevation (GPS) is only off 8+ feet and the coordinates (GPS) are +/- 1 second. I too have seen many dimples like these but never think about their origin. My 16oz PB wouldn't begin to make a dimple (a steeper pin hole maybe).

Sorry, I just looked at the link that John had put in & you are correct.. it took you to another benchmark page that was very special too, but, for other reasons. This link should be correct...sorry for any confusion that this may have caused. There was one person (Imapackrat) that also took a picture & it also shows the marks fairly well.

 

~Shirley~

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Some similar markings are found on: JB1220 that I found a while back. I don't see any reason for repeating the elevation tho.... Someone with too much time on their hands?

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Anyone think of contacting the Geodetice Survey people and asking them about the marks?

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I am 100% sure they are nothing more than defects in the disk, either from rolling around in a truck or storage container or from someone vandalizing it. There is no logical survey reason for them.

 

When you see info stamped like JB1220 its an indication that they did not have any stamps with them. I once found a USG disk that was completely stamped out with dots.

 

Here is another, seems they were missing some dies.

 

AC5814_TT3L-3.JPG

Edited by elcamino

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I am 100% sure they are nothing more than defects (snip)

 

When you see info stamped like JB1220 its an indication that they did not have any stamps with them. I once found a USG disk that was completely stamped out with dots.

 

(snip)

Yes there is a reason,

Which I stated above,I gave the reference material on it and the book and page.

On a reset a ball peen hammer is used to peen out all the old stampings to be replaced by the new stamping.

 

Yes on the One disc it is vandalism by JB.

 

The others are still???? as to what exactly they are for,but I have found this on several hundred of the discs,the # of dimples differ from 1 to several,and now the more I look the more I find....so there could not have been that many rolling around the back of the truck,or elsewhere.

 

Especially when the area is so diverse,the same crew's did not put them all in.

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Well its a mystery that will never be solved for sure. btw-I was not saying the punched ones were vandalized. As for peened, I have never ran across one like that but I did once do that to one BM when the construction inspector thought he was saving a new disk by reusing the old one in a new bridge abutment.

 

I know of several Triangulation disks around here that actually have holes thru the disk, about 1/8-inch dia. and off-center. One we found was destroyed, so I took a sledge hammer and removed the disk. What I found on the under side amazed me. It was the USGS legends. Top side was US Coast And Geodetic Survey and the bottom side was U.S. Geological Survey. A brass stem was solder onto the disk. These were set in the 1954 time span and the disk are more flat than most others. I sent it to the NGS state advisor 'cause he had never seen such a thing. I wish now I still had it.

 

I will try to find one and take a photo to show the hole in the disks. I check all my images and I don't have one to share now.

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We recently recovered benchmark ROAD and all 4 disks had a single hole drilled in them. The triangulation disk, both RMs, and the azimuth mark had the hole near the center of the disk. The azimuth disk's hole has filled in with dirt.

 

Curiouser and curiouser. ;):D

 

John

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John

 

That is the hole I saw in the same style disk. It is the same time frame to, 1953-54.

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John

 

That is the hole I saw in the same style disk.  It is the same time frame to,  1953-54.

 

It's to bad we cannot see what is on the other side of these marks. We wonder if they too, have the USGS atamp on the underside.

 

Anyone out there have one of those tiny snake cameras like they use for going through arteries?? That is the only way I think we will ever know for sure....

 

Shirley~

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These holes that are off center were pre-drilled by the agency setting them. They had a theory for awhile where the disks would set better into the wet concrete by letting out air as they were installed.

The problem came about when some of these were used as Horizontal marks and there is confusion as to the centering point. The procedure was abandoned with time.

 

Regards

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