FRUSTRATED

I bought some 2-section rods(CST), years ago and as always, one of the first things I do is to set it on my "jig", which is a small hole in concrete, underneath a plumbed id cap for rod-top.

I set one rod on . . . about a hundreth off.

Others . . . not so good

The worse was about 4 hundreths off.

I eventually got most of them to set within a hundreth or so . . . couldn't get them any better, but even then, each top section had to be "matched", to the correct bottom section to work.

One rod, I could never get to plumb properly, no matter how hard I tried.

Never had such problems with the graphites or the Crain rods

I had the same experience with a SECO pole. I'm pretty sure the bubble glass was deformed, because it would not stay set. Infact, you'd often see the bubble suddenly move for not reason while in our jig. We have 8 SECO 2m poles, and only one had this problem. We evenutally got a new bubble.

Going back to the OP, when you get a new rod, you have to check and adjust the bubble. Your boss did the right thing, in theory. Maybe he did it wrong, or maybe the bubble is loose or bad, but you should check and adjust your bubble before you use the equipment, and regularly there after...

I concur with the checking of the new gear.
-some rod bubbles "wont" stay adjusted and need to be replced, unfortunately, this information becomes apparent over the course of time and frustrating days.

I'd advise against getting on public message boards and going off to often...

So why did you have to wait 'til you got back to the office to check your backsights? Whenever I shoot my backsight, right after setting 0°, I measure the backsight distance, looking for things just like that. After the first couple,you'd know something was wrong. BTW, what's the minimum allowable closure in your state? 1:11,900 used to be OK in a lot of places: not great, but legal.

Traversing, turning sets and using a rod as a foresight?
jud

If your closure is legal, and you know you had a consistent offset in the rod, can't you compensate each leg for that offset before doing an overall traverse adjustment?

If that consistent offset is the major contributor to the errors, then compensating for it should give you a better closure even before doing a closed-traverse adjustment.

It'll take a little time, but less than re-shooting everything.

Bi pod

> Traversing, turning sets and using a rod as a foresight?
> jud

Almost like using a tape without a plumb bob...

😉

I think that everyone has had those results at one time or another.

That is the reason I use tripod, tribrac and prism target for backsite and foresite.

Prism poles are for sideshots mainly.

Mini prism setup first or a prism pole second for setting monuments.

I do not like using a prism pole for control points.

Check and adjust every tool regularly.

It will pay off in the end.

0.02

Yeah I spoke with him. He said he didn't have his glasses on when he did it. 1 in 10000 is legal, but we aren't going to let loose control like that slide. I'm pretty sure what they will do is take the back sight distances and cook the front sights to match since we know the back sights were good. I fixed the pole, and can't wait till the next one because the angles were great. It worked out to like 2 seconds per.

Our software tells us the differences on the back sight every time. My I man didn't bother to look/let me know they were consistently off. I may keep the collector with me at the pole from now on.

:good: :good:

> > Traversing, turning sets and using a rod as a foresight?
> > jud
>
> Almost like using a tape without a plumb bob...
>
> 😉

measure 3x with a micrometer, mark it with chalk and cut it with an axe.....

While not the...

greatest closure, its twice as good as it needs to be here in CT.

0.02' Out

Assuming by your comment on the backsight differences that you know it is just consistently long or short, not side to side. That is the foresight rod man always had the bubble facing him and the prism facing away.

A 36 acre perimeter traverse is on the order of 1 mile. Unless you had tremendously unbalanced legs 0.02' per leg is just going to give you a scaling error. Having readjusted it your self, you now have no way to give some dimension or direction to the error per sight. i.e. you have destroyed the evidence.

As a simple check adjust all foresights with that 0.02' and recheck the closure. I suggest it will not vary significantly from the field value. Why did you have to process data to know if you had a good closure. A proper field procedure should have given you 1 redundant angle and 2 redundant distances. checking into the first point back is never enough, you have to occupy that point and check into the next one. The difference if those 2 checks is your first check on precision. Then you compare your intitial back and fore bearings against your final back and fore bearings. The worst difference is your initial angular precision.

Your best check at this point is to occupy at least 4 points at or near the corners with precision GPS.

Use this as a learning experience for you, your boss and your crews. There is no single guilty party, all are to blame. Getting something positive out of it and move on.

I assume you have now put both rods on the same points for comparison purposes and as a check on possible offset differences. But then I could be assuming too much.

How many legs and how much spread in them among other questions I want to ask?

Any other field checks such as observing a monument from 2 different stations?

Any cross or corner diagonal tie shots?

Paul in PA

Dear FRUSTRATED, Prism Pole Tripod Needed

>It can't be the brand new rod that came with the instrument...it's brand new. I check it anyway, and sure enough it's out of plumb about two hundredths!

You know, a permanent fix is to buy a good quality prism pole TRIPOD that enables the bubble to be checked at every set up. If you order a pole with a more sensitive level vial on it, you should expect to be able to center the prism/target (at HT = 5 ft.) over the ground mark with an uncertainty of less than 0.5mm if the pole hasn't been abused and the point is sharp.

The other piece of equipment to carry is, of course, an Allen wrench to adjust the vial at the station if it is found to need it. Would recommend both.

In case it isn't obvious how to adjust the vial, you just plumb the pole to a position where the bubble position is a mirror image of the bubble position when the pole is rotated 180 degrees. Do this in all four quadrants and adjust the level vial so that the bubble is centered. Check by reversing the bubble position and repeat if necessary.

If using the prism pole (leica 360 prism on 1.3m pole) for control point measurement I always do the following:

• Measure two faces
• After first face rotate pole (and yourself) 180 degrees, and record the second face reading
• make sure that the flat edge of 360 prism is perpendicular to the instrument

If you like you can review the measurement and compare the differences in slope distance as well as zenith and horizontal angles to make sure they are acceptable.

Using this two face pole method for both backsights and foresight, I've always achieved very good results. This is all done solo too, using the controller on the pole, and is a very fast and efficient way of doing surround surveys for boundary reinstatements.

This is why people have got to buy from reputable dealers. Not from online, garage-based stores or retail outlets that provide no service or support. Not saying it happened here but any reputable dealer would check out anything with a vial, optical plummet, etc.

There's nothing wrong with that closure. Yes it could be better, but it certainly isn't anything to lose sleep over.