Ok. So maybe the thread title is a little extreme. But not by much. For years I've observed that some objects are detectable with magnetic locators and some are not. Recently I've been testing magnetic locators for a project and I've taken 5 rebar from the same bundle and each rebar produced a significantly different signal strength. The claims that an object of this size or that is detectable at this depth or that is somewhat misleading as there are plenty of examples of such objects that have no polarity or a weak polarity. It may be that you can detect a 1 inch bar from a depth of 5 feet. It may be that another 1 inch iron bar cannot be detected from a depth of an inch. Another issue is the direction of polarity, negative or positive. This affects the received signal strength. I don't pretend to know all I would like to know about magnetic fields, but observation during my 20+ years of surveying has demonstrated that you cannot know that an object is not there simply because there is no signal from the locator.
I provide sales and support for some very advanced equipment. I use that equipment daily in my own business and it is what allows me to be productive as a solo operator. Having said that, I have said and continue to believe that the most important tool in a surveyor's truck is the shovel. The second most important tool is the hammer. We are called upon to find or leave as set monuments that define the boundaries of real property. It's the basis of what we do. The shovel, in many instances is the finder and the hammer is the setter. Both are important, but for retracement the shovel is king.
I recently took a small job (or what should have been a small job) finding the corners of a lot and staking one line. The lot is a simple four corner lot in town, 60'x170'. I found the first corner in a shared asphalt driveway fairly easily. I then worked my way down the street line. I was unable to find my other front corner and continued down the street, finding two more monuments that fit with the first. I always try to do this because it is possible that the first stake was not correct. I've even seen two front stakes be right with each other and wrong with the subdivision, so it's good practice to tie in an adjoiner both ways if possible.
I then went to the back. I found one stake with old flagging on it, but it wasn't the same character as the rest. It was an old carriage bolt with a 1/2" diameter shank. The normal material for this subdivision is 5/8" sucker rod (a smooth sided steel rod). I tied it in, but in my mind placed an asterisk beside it. I was unable to find the other back corner. I proceeded to other back corners. The next back corner was a 5/8" sucker rod, but it was sticking up about a foot. This seemed uncharacteristic, so I collected it, but also placed an asterisk by it in my mind. I continued on and finally found a corner that had the right feel to it. I went the other way and found a back corner in the other direction that matched my expectations. The distance between them was within a couple of tenths of record. The carriage bolt was off by about 2 feet from the record, holding these two back monuments. I then used these to rear monuments and staked where I suspected the corner should be. Sure enough I found a 5/8" sucker rod very close to record call. I then went to my other back corner and confirmed that it was gone by digging a hole. It was right beside a drainage inlet and was very likely removed when the box was constructed so I set a new monument.
Back to the front, I was now ready to set the front corner that I was unable to find. However before setting the stake, I navigated to the calculated position. I didn't see any reason for this monument to be missing and the original surveyor clearly had marked the lots originally. So I dug the point also. Sure enough, only a couple of inches below the surface I found the 5/8" sucker rod in place.
The only way to know for certain that a monument isn't there is to dig. Now the question - how deep should a surveyor dig? I don't have a definitive answer for this. There is a matter of practicality. Not just for the effort involved, but also a point where a deep, deep monument doesn't offer much to property owners to know where the boundary is. Typically, I will dig a foot, use the locator and see if there is a signal. I also look at the soil to see if it appears to obviously be fill (coloration and debris).
Another thought about this job... I'm going to tell on myself. I gave a lump sum fee of $250 to do this. The lot owner thought it to be too high! In all, I spent about 5 hours in the field on this job - way more than anticipated. I don't think that this entitles a surveyor to provide a less than excellent service. Even when you start seeing that you are down to minimum wage, you still dig the holes and you still set the stakes.
Let me ask... did you try any other brands of metal detectors on this? Did you try searching, AFTER you found it, and did this Sucker Rod have any signature?
I have not yet found one that had ZERO signature.... But, I have found them quite weak, and you had to get within an inch of their tops, to get anything.
I have a magnet I carry on the ATV. I set the magnet on the tops, of these "Low signature monuments", for a second. Now, these low signature mons give nice loud signal.
N
I hate it when I can not find a corner, I know it is not true, but I believe in my heart that the previous Survey set or found every corner on the tract. I do the same thing Shawn find enough corners that are the same type and size for me to feel comfortable to calculate stake points, then look and dig a little before I set the new rods. I will look 3 or 4 times before I convince myself the rod it not there.
I hate it when in an area that as not had anything built, and the corner is not there, It was to much trouble to cut line, or walk area to set it. but the other corners are in.
Nate The Surveyor, post: 391358, member: 291 wrote: Let me ask... did you try any other brands of metal detectors on this? Did you try searching, AFTER you found it, and did this Sucker Rod have any signature?
I have not yet found one that had ZERO signature.... But, I have found them quite weak, and you had to get within an inch of their tops, to get anything.
I have a magnet I carry on the ATV. I set the magnet on the tops, of these "Low signature monuments", for a second. Now, these low signature mons give nice loud signal.
N
I didn't try another detector on this one. I did try my detector on this a second time and it was still no signal. Some weak signal stakes are just as you say. Within an inch, they give a signal. Often I see that the signal beside these rods is stronger than above it. I suspect is the field direction that causes this, but I don't know for sure.
I've done the same with a magnet. One thing I want to see, but have not tested, is whether this re-polarizing of the rod lasts or if it loses the polarization again after some short period of time. Have you ever returned to one that you re-polarized to see if the signal remains strong?
I use this GA-72 but the brown military version. On the 3 setting if it reads 6.01 I turn it down to the 2 setting, if it reads 0.36 I know I found the corner of a 5/8 or 1/2 rod, the 3/8 is around 0.31. I still dig on other hits, but it does help to eliminate junk metal in the area.
Scott Ellis, post: 391360, member: 7154 wrote: I hate it when I can not find a corner, I know it is not true, but I believe in my heart that the previous Survey set or found every corner on the tract. I do the same thing Shawn find enough corners that are the same type and size for me to feel comfortable to calculate stake points, then look and dig a little before I set the new rods. I will look 3 or 4 times before I convince myself the rod it not there.
I hate it when in an area that as not had anything built, and the corner is not there, It was to much trouble to cut line, or walk area to set it. but the other corners are in.
Exactly right, Scott. I hate with a passion looking for stakes that should have been set in recent some recent survey but that you know were not set. For example, it's a boundary with 7-8 corners that were supposed to be set and you've looked for 4 already without a trace and you still have 3-4 to go. You still have to do your due diligence to make sure it wasn't set, and then, once you are convinced, then you have to actually go in and set it. It easily triples the field work regarding reconstruction.
My gather on this is that the DEFAULT or "Resting place" setting for a monument is to have the primary signature come out the ends. However, various factors, can upset this, and make the primary signature come out the sides. Welders have told me that you can smack metal VERY hard, with a hammer, and re-align this signature. (IF when trying to weld 2 pcs together, and the signature is wrong, the melted welding metal just runs off, and won't stick) So, their solution is to smack them. From all the conversations I have had with them, my take on this is that they PREFER to be coming off the ends... but can be made to come off the sides. So, I ASSUME that after touching it with a magnet, that it stays that way... Based on all I know, I'm pretty sure that's true..
What upsets this polarity in first place is HARD POUNDING. My experience bears this out too. ALL the bad polarity monuments I have ever seen, were in very hard soil.
Thanks for asking.
N
I think certain things could change the polarity of the monument or reduce the magnetism to null, although I can't prove it. Think about lightning strikes, I would imagine if lighting strikes close to a monument that the magnetism is going to change.
I dont know anything about polarity, or any of that, but I am glad to see others sometimes have rods that a metal detector won't sing off at. I have had arguments with know it alls that it is impossible for metal to not set off a metal locator. I am also very thankful to have read the OP's post this afternoon, giving me faith in surveyors doing it the right way. let's just say I have been doing some unnecessary work today because someone couldn't do more than the bare minimum, and shaved away from that a tad too.
Sometimes you need to dig in the spot where the detector goes quiet instead of where it squeals. Many times that dead spot holds what you were seeking.
Holy Cow, post: 391376, member: 50 wrote: Sometimes you need to dig in the spot where the detector goes quiet instead of where it squeals. Many times that dead spot holds what you were seeking.
I experienced that last week. Unfortunately it ended up being a large portion of some ancient machinery...
I searched for a section corner that was recently set by another surveyor. I looked and looked with a metal detector, and even dug without the benefit of a ring and just couldn't find it. We had coordinates on where it should be and navigated to it with GPS. I finally gave up and later called that surveyor. We set a time and met at the site. We walked out with a metal detector and found the ring immediately. I was pretty embarrassed.
It was clear ring and pinpointed the monument at the same place we were looking before. I was pretty sure we used the same locator and it had the same batteries. The only difference was that the first time it was a very cold day. (but I've found pins on cold days too.)
Found the polarity on any to be opposite with my hound dog locator
Do you like the hound dog?
Yes, for nothing else but the light weight and the packability. My speaker went out so I shipped it back. The whole polarity thing is a trust but verify, like everything else we do.
It seems to me that the only colleagues we have, that are practically interested in ferrous metal polarity, and magnetism, are the welders. On this note, I'm sure there is information available, on this subject, in welders books, or the professional pipeline welders books.
It sure is an area of liability, no matter how you slice it.
Nate
The sweet spot will move as you dig.
I know of a few r5s that you can set a schonstedt on and not get a signal. Recently I found 2 r4s that I set and could not find with a locator. I did not know about the magnet trick. I will have to get one soon. Thanks.
I love my magnetic detector but there are drawbacks like wire fences and steel guard posts. A few times I've pulled the tee post to locate the rebar. Then there is junk and then the favorite in my area is rocks that zing it off. Although I actually found a 1/4 stone down about 18 inches in a farmed that set off the detector. Thought the corner was lost. When I got there decided to see what else may have been set and something buzzed off about a foot and a half from proportional distance. Dug down and found a nice marked stone along with remnants of fence posts against it. Seems the field had been leveled up a bit and the corner was in a low spot covered up deep enough never got whacked by the plow. A shovel and a mag detector ARE important surveying tools.
We went to a 10+ acres today that was part of a division made in the late 70s by a company I had worked for and knew what to look for.
Witness trees were called for and all except two were long gone pines with no stumphole in sight.
The two remaining witness trees were blackgum displaying multi colored green and yellow to red leaves.
At 4 of the locations there were tpost only at first observation.
Our first find was a 6in cutoff end of a tpost, the second was a 1in cable that lead off into the roots of the dynamic forest to the west. Dynamic forest = grown over non value growth of shrubs, persimmon, sweetgum, etc where nothing of value was planted and everything there is by chance, only benefit is that the ground will not erode.
Found tpost at 4 out of 4 offroad monuments. Took pulling each tpost out to locate the 3/8in cold steel smooth rods that the tpost were driven down touching the rods.
I can not count the number of rebars that I've found that were rusted to tposts driven down touching them.
Cold steel smooth rods hold their form and rarely make a rust ball around here.
One reference rod in the margin of a county road was touching a 10in creosote post (former power pole) in a newer service line that had taken out the witness tree.
The other road corner reference was taken out by the installation of a corrugated culvert where there had been a rut in a native dirt road in late 70s for the water to pass from the higher side of the road to the natural downslope, no creek involved.
I've noticed that identical rods, nails or other monuments or hubs will have a different degree of signal after they have been in the ground.
The more an object has bonded to the ground by way of developing a rust ball bond with the ground the higher the signal.
In the late 70s with my first Schonstedt I found an 18yr old 60d nail with a rust ball the size of a grapefruit and it was easy to find in comparison to ones that had not developed a rust ball.
In comparison, the less affected the material by the ground the less of a signal.
Some 60d nails are very hard to find unless the locator is directly atop them.
Ancient tempered and cold steel items always sound out with excellent strength as well as iron pipe joints and the ends of high grade fence wire.
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