I carry one when I am in the field. Here in the office, not so much.
I sometimes hand it to inquisitive neighbor's and challenge them to hold it steady over a point for ten seconds. Do the same with the prism pole. Not so easy you see. I once gave it to an attorney so he could check a view corridor from his deck and he fumbled it so badly that I almost peed.
Stay plumb my friends.
Surveyor Dean, post: 363197, member: 11367 wrote: Plumb Bob's are cool but an fixed object like a rod with point is easier for line of sight and in my opinion more accurate just for the simple reason you can sight the bottom of the rod with cross hairs and not judge line.
But there are many times that I've run into the issue where the lower half of the rod is not visible due to obstructions. So I can't look at the tip and give line/site the rod as easily. A plumb bob (in the hands of someone who knows how to use it) is very quick and reliable to give/read line above the actual point on the ground.
skwyd, post: 363480, member: 6874 wrote: But there are many times that I've run into the issue where the lower half of the rod is not visible due to obstructions. So I can't look at the tip and give line/site the rod as easily. A plumb bob (in the hands of someone who knows how to use it) is very quick and reliable to give/read line above the actual point on the ground.
Key being Someone who knows how to hold a plumb Bob string over your head to get a accurate line.
Richard, post: 363088, member: 833 wrote: I still carry mine, it's attached to my field bag.
12 oz, enough oomph to drive tacks, clouts.
I have about 2.4 metres string and it makes a fantastic Bolas for those times I need to pull garden shrubs aside and tie off when they interfere with line of site. Works very well.
Years ago I jumped into the F-250 my boss had who being a lead foot sank the throttle and launched us towards our next set up.
Unfortunately the plumb bob string was still outside the vehicle, wrapped around some gorse whilst the brass works was secured on my belt!
Thankfully it separated from the plumb bob without too much fuss. I can still remember the thwump as the cord left the vehicle.
"...enough oomph to drive tacks, clouts."
NOOO... Dad would have killed me for doing that!! Could be the first thing I ever learned...
Surveyor Dean, post: 363678, member: 11367 wrote: Key being Someone who knows how to hold a plumb Bob string over your head to get a accurate line.
Absolutely true. And I think that skill is something that isn't being perpetuated to new surveyors. That's unfortunate because it is a good skill to have.
A plumb bob and optical square. An inseparable and powerful combination and remarkably accurate.
Last week I used the string for my bearing to a very close point. Drag (extend) string across stn and object I'm measuring to, for line, and read. Book distance manually.
Yep, the skill was keeping the bob steady during a shot. Real steady if it is a short leg. Like shooting a rifle, establishing a stable body position depending on conditions is key. From steadiest to wobbliest as best I can remember:
If instrumentman can see the string, i.e. it's a short line so atmospherics are not a concern.:
- Point visible to instrumentman. With bob touching ground, point at tack center or disk dimple with tip with bob tip in IM's scope aperture. Prevents him mistakenly shooting your boot eyelet or oddly arranged forest duff.
- Point obscured at ground level. Sit cross legged with bob arm on one knee, exposing a few inches of string. Jack up knee as needed.
- 1-2 feet. Kneel on one leg, use other knee to rest arm on, other arm can stabilize loose knee a bit.
- Point obscured by 2+ feet. Crouch slightly with arm pressed against one thigh, only exposing a few inches of string.
- Obscured by 3-5 feet. Press arm against a hip, or rib cage, orienting to assuage wind problems.
- 6+ feet. Assume the angel's position, hands clasped together holding the bob, legs spread a bit, head bent down so you can see the mark, press an arm against a cheek or forehead if possible. Above your head, work on breathing control, etc., and pray. Good to only +-0.05' in my opinion.
If the line is so long the IM can't see the string, deploy yer Gammon Reel where he can see it, if air shimmer is present, may several feet higher. The lower the reel the better. Do not deploy the Gammon Reel if he/she can see the string! If the IM can't see the Gammon Reel, all bets are off and long distance targetry should be used.
I'm dismayed apparently modern optical survey crews have no clue concerning shooting a range pole (with huge phase error) or a poorly oriented fixed target or prism on a pole or tripod at very short distances is AOK, when a plumb bob string shot for angle is much more accurate.
Now, let's talk about wind and the actual observations. I believe that a plumb bob beats all other targets in short line terrestrial observations because it has no phase errors, tribrach problems, shooting a prism center or prism targets (if part of the assembly) misalignments, and accurately prevents centering errors which a forced centering traverse ignores, if the IM can see the string.
But, in plumbobery, tired people can degrade the observation. Let's go through an observation, tough shot where the foresight has to carry the string or Gammon Reel target high and it's windy and he's tired. It's solved by communication; the foresight guy continually yells (or uses comms) to say "good, good, bad" as he watches the plumb bob tip dance around the mark. Eventually the IM averages all the good calls into his actual observation, weak sauce, 0.00-0.06', you make the call.
The only downside of a plumb bob is wind, which has little effect on a fixed target on a pole or tripod. The problem can be ameliorated by protecting the string with a leg, or by placing the body upwind to provide a windbreak, using a lathe as a crutch, or a much heavier bob (mine surveyors use 20-50 pound bobs immersed in an oil bucket with steel wire to transfer angles between levels, they're real jumpy about air currents).
The loss of the plumb bob string as a short leg angle observation target has degraded traverse leg accuracy. But who cares these days, RTK GPS is good to 0.04-0.10' absolute so short leg angle observations now mean nothing, bad angles are fluff, *unless* you're shooting for +- 0.02' accuracy. It appears 0.1' is good enough for most land surveying (not engineering surveying when things have to be tight) so goodbye plumb bobs.
I still got mine with a Gammon Reel on it, for the odd short shots using a total station and a steel tape.
I couldn't tell you the last time I carried on a regular basis. At least ten years. I work alone, so there isn't anyone to give line to with a bob.
I always carry a plumb bob. I use it to drive in nails, make sure I can see between trees on traverse, and mark line. I used a little 12 ouncer today to stake a property line. Set two points with the gun and then had to set about four with the plumb bob eye balling the remaining four, perfect if I do say so. Also, was going to attempt to flag 400' line yesterday in thick cover by eyeballing it. I felt pretty confident when I went past two marked trees on the correct sides. Worked out pretty well.
Norm Larson, post: 363006, member: 7899 wrote: Our crews are in the field and the schedule guy forgot that we had an appointment to punch some monuments. That is bad, but, isn't the point. These are in hand wells (cases) so we had to find a plumb bob in the office and I know that there are plenty, but, we couldn't find a one. Yes, Plumb Barbara is one the job today... After 20 years of being a decoration. Hellofa Friday so far
I have an 18 oz that never leaves my vest. We use it at least once or twice a week. Sometimes more.
what's a plumb bob and why is bob out of plumb?
I couldn't even find one of the 64oz bob's that I own. I bought one because I had an entrance to a building that was several floors high and I wanted to place a bed of sand, hang the bob from up high and watch the changes. I had one on my desk set up that way and we had an earthquake. The patterns from the quake in the sand were very cool and I wanted a bigger one. Never set it up though.
The crews had bob's on them and had some of our office bob's as well. My vest and belt are long pillaged though and have been bob free for years.
I don't think that Claudine Gammon would appreciate being compared to a slab of pork 🙂 She's (?) listed as the inventor.
Patents by Assignee Gammon Reel, Inc.
Construction string reel
Patent number: 4662078
Abstract: Disclosed herewith is an improved reel assembly for surveyors and other construction trades wherein the resilient member that retrieves the plumb line or string is entirely enclosed in the spool assembly that is contained within the housing of the reel assembly. The spool assembly is formed so that it is difficult to obtain access to the resilient member thereby precluding inadvertent release of the spring assembly.
Type: Grant
Filed: June 2, 1986
Date of Patent: May 5, 1987
Assignee: Gammon Reel, Inc.
Inventors: Norman P. Gammon, Phillip R. Gammon
I guess that Claudine did something in 2000, but it wasn't inventing the reel, I've used it since the early 80's. I stand corrected!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Surveyor reel housingPatent number: D446733
Type: Grant
Filed: November 8, 2000
Date of Patent: August 21, 2001
Assignee: Gammon Reel, Inc.
Inventor: Claudine Gammon
James Vianna, post: 363787, member: 120 wrote: what's a plumb bob and why is bob out of plumb?
Everyone knows what I Plumb Bob is, but what I can't figure out is....I found that cap on top and could tell that was where a triple-A batter would go, but when I unscrew it, the dang battery doesn't fit. So just how to you get the battery installed? The guy @ batteries plus was no help at all.
Tom Adams, post: 363808, member: 7285 wrote: Everyone knows what I Plumb Bob is, but what I can't figure out is....I found that cap on top and could tell that was where a triple-A batter would go, but when I unscrew it, the dang battery doesn't fit. So just how to you get the battery installed? The guy @ batteries plus was no help at all.
Battery? You must have an exotic Bob.
Mine are female because inside the cap is a baby Bob..........
:woot:
Tom Adams, post: 363808, member: 7285 wrote: Everyone knows what I Plumb Bob is, but what I can't figure out is....I found that cap on top and could tell that was where a triple-A batter would go, but when I unscrew it, the dang battery doesn't fit. So just how to you get the battery installed? The guy @ batteries plus was no help at all.
Once you install the battery, be sure the bob is properly adjusted before use.
C Billingsley, post: 363818, member: 1965 wrote: Once you install the battery, be sure the bob is properly adjusted before use.
Yep, you gotta calibrate it so it points to the correct "down" in your local zone!
