What's the best way to check for rod runout?
Follow-up question: Who makes the truest rods, in a one-section rod that goes to 7 feet maximum?
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Laser Interferometer
What's the best way to check for rod runout?
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Roll it on a sheet of glass.
You might want to remove any bubble and separate it into sections.
If you have a GPSS with eBubble, you can set the pole vertically using a pole bubble, calibrate the eBubble, then spin the pole. If the eBubble changes you probably have a bent pole (often it the brass adjuster right at the top, which tend to bend if the pole is dropped)
Two instruments at 90?ø to pole?
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Am keen to see which pole is best too. Think Mark Silver posted a long time back he found it hard to find a perfectly plumb pole over its entire length, think it was under 3mm that was hard to get which from the poles I've used (Leica, seco) seems about right.
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Accurate work requires a peanut prism and working on your knees.
The other day I had a strange experience which might have nothing to do with rod runout, the bubble, gravitometrics, or anything. Put the LS-plus on the usual rod with the bipod and walked down the street to look for faintest of marks like lead and tacks. Looked back and I'm thinking, that rod ain't plumb! So I went and used my oldest junior rodman sense of "plumb" while ignoring the bubble and shot it again. Huge difference. Then I turned the rod 180 because I just read about that on Surveyorconnect and shot it again. Way huge difference. Like half a foot. So at 180 I did the same "never mind the bubble, do your hands tell you it is plumb" rock the rod and shot it again. By this time the party chief was P.O. and said box it and get out the total station but the boss said average it and see what happens. Solo is hard when you have to supply all the dialogue. The averages were tight enough to use the coordinates for a resection and move on but I came home to check the bubble and it's hardly out a quarter bubble. Leaves me thinking the bubble is worn in its casing and got bumped out and bumped back or the Santa Cruz Mystery Spot was translocated to Seattle that day. I'm sure there is an explanation and a fix but I am resisting the urge to throw that rod as far as I can and get a new one.
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It's called "Care of equipment".
Our rod always travel in a padded bag AND within that each has its own protective plastic tube (as used for plumbing - (the other sort, that uses water!). The only knocks they can get is when the surveyor falls over.
In the office we have a plate on the floor with a centre hole and a 5/8" nut fixed up on a wall bracket, set by theodolite to be exactly plumb. Screw top of rod into nut, extend so point goes into floor hole, adjust bubble if necessary.
And I'd agree, the "feel" of the rod always tells me if there is a plumb problem. The bubble is just there to get in the way when you need to be hard up to something.
@chris-mills there are moments when I think the bubble is only a fiction and the only true rod would be one without any asymmetrical weights to confuse the rodman.
Set the rod on a mag nail?ÿ dimple about 4-5m away from the leveled total station. Level the rod with the bipod, keeping the bouble along the pole-instrument line. Center the crosshair on the tip of the pole and set the Hz angle to 0, then sight the centre of the nodal prism you have on top of the pole. Check Hz angle to be 0, if not, adjust it to 0. Adjust the pole bouble left-right away until the prism center coincides with the crosshair and measure the Hz distance. Turn the pole 180 deg, level and measure the Hz dist. again. Adjust the pole bouble back-forward?ÿ until you read the average Hz distance. Repeat the whole process until you measure the same distance in any position of the pole ( every 90 deg) and the crosshair matches the prism center while Hz angle reads 0. This process should be repeated for different pole heights. I have an over 20 years old 5' long Sokkia pole that I still use with a Leica adapter on top and a Leica circular prism (the nodal one) and I managed to get the runout at the prism level (pole not extended) to about 0.5mm using an 8' bouble on the pole.
My rods hang in fishing rod slings mounted on the topper.?ÿ Keeps them out of the way and the webbing absorbs any road vibrations.?ÿ Even on the bumpiest of roads they just swing back and forth.
https://youtube.com/shorts/z7oo36mYL8U?feature=share
I know if I have a bent rod with this method because I will chase the bubble all over when I rotate 90s and 180s. Also roll on flat surface???
@ramses How do you adjust the bubble for different rod heights? I'm under the impression the bubble indicates the same regardless of the rod height. If your rod is not straight, then you can only adjust the bubble to work at one specific height.
The bubble only relates to the rod section on which it is mounted. If the extended section is not true then perhaps you should get a different rod.
Would you use a levelling stave where there was a distance error at a joint?
@lurker I usually use my pole fully collapsed. If I need to extend it by 2', I can see a run-out of 3mm at the prism. I tried once to adjust the bouble with the rod extended and the best I could do was 1.5mm run-out. I do construction layout for a concrete forming contractor and in this type of work you can't really stand behind the pole and look at the instrument,?ÿ so a well adjusted pole bouble is a must, if you want to be within tolerances. The best way to cancel out the pole imperfections is to take a shot, rotate the pole 180 deg then take another shot and average rhe readings. I can never do that as I am always setup on the edge of hole, or the edge of a concrete form. I my experience there is no perfectly straight pole. To keep things under control I even sharpen the pole tip on my own lathe.
