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chris mills
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August 12, 2017 5:54 am  

This thread prompted me to dig in the store - quite a collection so I'll make several posts.

We had a viaduct to survey for new bearer pads. The client wanted the exact positions and levels of each beam, both ends. Several sizes of beam and the height from ground varied between 2 and 7 metres high. About a dozen beams on each span and 15 spans.

This little device, with lots of extension rods on the bottom, enables the prism to be held a given distance from the cross beam face. The prongs are adjusted to suit the width of the beam to be measured and then it self centres. The cross bar is a known height above the prism. We could get scaffold access because there were roads and a railroad under most of the spans.


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chris mills
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August 12, 2017 6:00 am  

Another thing held in the air. We needed to monitor a number of houses with (rapidly) ongoing settlement, so exactly the same point was needed eqch time. This little device sits round the house corners, held at damp proof course at low level and the top butts up under the eaves board at high level. Again, used with extension rods to get the height. The targets are a fixed distance from the centre and top/bottom so a single instrument set-up can observe a number of houses.



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chris mills
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August 12, 2017 6:08 am  

Things to get where you cannot reach - these were used on various mechanical plant to get levels.
The yellow device has two scales reading from the base and can be pushed into gaps on the end of one or more extension rods. It has a stainless steel shim on the bottom to enable it to slide smoothly.
The white contraption was designed to get levels on the underside of some roller frames. The scale can rotate in the circular holder (plastic pipe) which sits over an close fitting piece of pipe. Guides inside hold the scale vertical. The top surface of the base has a 5mm wide indent against the holder, so that any burrs on the edge of the roller frames do not put the unit out of level. Again, this was a job where you could only just reach in to get at it.


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chris mills
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August 12, 2017 6:19 am  

Precision probing. This little device was designed to get at a precision bearing face, where the gap to get in was less than 2cm. (and at arms length). The bearing was about 90cm. diameter and the task was to set up an outer ring exactly (within 0,2mm) concentric, The outer ring was around 4 metres in diameter.

The device has a spring loaded pin on top, so that when the body is pushed against the bearing casting the pin touches the machined bearing edge first and pushes out under the spring. The body of the device keeps everything square and horizontal. At each location around the bearing (12 points in all) we set up a calibrated total station to look square in to the bearing and read the distance to the bearing. The device was then taken to the outer ring position and read again, the difference being the offset of the ring from the bearing. When all was complete shim sizes were calculated to set the outer ring truly concentric.

Fortunately, when all was done 500 ton of machinery rotated without the slightest sign of any vibration.


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chris mills
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August 12, 2017 6:30 am  

Last one!

This device enables verticality to be measured underwater to 1mm accuracy. It was designed for use in competition swimming pools.
One of the problems of putting the spirit level underwater to measure at the required 0.8 metres below water level is that any variation in tile fixing higher up can push the spirit level away from the wall. The orange blocks on this device offset the level by 10mm from the tile face, so it cannot catch on anything. The top target is set back by 10mm. so it represents the tile face position at the depth being measured..This also means that measurements can be taken with timing pads in place, without the frame of the pad catching on the spirit level.
The bottom plate has a plastic cage inside, which has been shimmed up to give the exact offset (third image).




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Richard Imrie
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August 12, 2017 11:34 am  

chris mills, post: 441643, member: 6244 wrote: cannot catch on anything. The top target is set back by 10mm. so it represents the tile face position at the depth being measured..This also means that measurements can be taken with timing pads in place, without the frame of the pad catching on the spirit level.

We "did" a pool recently, fortunately just before the pads were installed, to cut back the tiled ends to get within the 50m -0mm +30mm spec. (The photo below is just for show, we weren't actually surveying that bit - the RMT is on the spike again, which we used and the ends to mark out the cutting line).


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Brad Ott
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August 12, 2017 2:08 pm  

Richard Imrie, post: 441715, member: 11256 wrote: We "did" a pool recently, fortunately just before the pads were installed, to cut back the tiled ends to get within the 50m -0mm +30mm spec. (The photo below is just for show, we weren't actually surveying that bit - the RMT is on the spike again, which we used and the ends to mark out the cutting line).

The umbrella is obviously to help keep the solar panel from overheating.

Beer Leg dot com R O C K S ! !
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Richard Imrie
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August 12, 2017 3:38 pm  

Brad Ott, post: 441760, member: 197 wrote: The umbrella is obviously to help keep the solar panel from overheating.

Ironically, apparently solar panels work most efficiently when they are cool. We've actually ditched the panels and solar controllers - too much trouble with the low voltage cut out systems they have, turning our instruments off - now just direct hookup to a small car battery.


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squowse
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August 13, 2017 1:57 am  

jim.cox, post: 441255, member: 93 wrote: We had to locate 234 driven wooden piles for an as-built survey.

Height was not needed, just position. But still it was going to take quite some time to locate each centre, level the prism and measure.

So I knocked up a device to quickly and easily locate the pile centres.

It worked really well.

Yup - an inverted waste basket with an attached prism

(sorry about the poor photo - the autofocus on my cheap camera doesn't like the wire mesh)

The piles turned out to be bigger than expected ( 300mm vs 250mm ) and it did not fit over them as planned, but it was easy to get the centre just sitting it on the cut ends.

So what's the best qizmo you guys have made?

Is your waste paper basket back in use in the office yet?


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jim.cox
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August 13, 2017 10:22 am  

squowse, post: 441826, member: 7109 wrote: Is your waste paper basket back in use in the office yet?

Sure is

=mjc=
.


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chris mills
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August 14, 2017 1:34 am  

Richard Imrie, post: 441715, member: 11256 wrote: We "did" a pool recently, fortunately just before the pads were installed, to cut back the tiled ends to get within the 50m -0mm +30mm spec. (The photo below is just for show, we weren't actually surveying that bit - the RMT is on the spike again, which we used and the ends to mark out the cutting line).

I hope you weren't carrying out the survey from the side of the pool as any residual instrument/prism error will double when you add the two sets of coordinates together to get the length.

I would always use three tripods set more or less down the centreline of the pool. Firstly I measure all those distances, to determine the prism/instrument constant under the days observation conditions, set that in the instrument and then measure each end from the opposite end tripod. Then any very residual errors cancel out.

The critical dimension is the "-0mm" one - nobody ever gets in a fuss over the "+30mm" since it is easy to pack out a timing pad. Looking at the photo, the timing pads seem to be Swiss Timing/Omega pads. Beware of the pad frame. They are stated to be 10mm pads, but the frame is around 13mm. so they don't sit back flush on the wall.The pads themselves have a +/-2mm tolerance so even if the pool is just in tolerance, once the pads are fitted it can be too short.

For those with interest in these matters, (or who can't get to sleep at night) the following go into the problems in detail although things have moved on a little since they were written.

http://www.scssurvey.co.uk/downloads/go5a.pdf
http://www.scssurvey.co.uk/downloads/go6.pdf


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chris mills
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August 14, 2017 1:44 am  

Richard,

There was a New Zealand Surveyor, Mike Elliot, who I worked with on the London 2012 Olympic Pool. He would be able to give you all sorts of info on what can go wrong with pools.


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Richard Imrie
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August 14, 2017 1:57 am  

chris mills, post: 441974, member: 6244 wrote: I hope you weren't carrying out the survey from the side of the pool as any residual instrument/prism error will double when you add the two sets of coordinates together to get the length.

I would always use three tripods set more or less down the centreline of the pool. Firstly I measure all those distances, to determine the prism/instrument constant under the days observation conditions, set that in the instrument and then measure each end from the opposite end tripod. Then any very residual errors cancel out.

The critical dimension is the "-0mm" one - nobody ever gets in a fuss over the "+30mm" since it is easy to pack out a timing pad. Looking at the photo, the timing pads seem to be Swiss Timing/Omega pads. Beware of the pad frame. They are stated to be 10mm pads, but the frame is around 13mm. so they don't sit back flush on the wall.The pads themselves have a +/-2mm tolerance so even if the pool is just in tolerance, once the pads are fitted it can be too short.

For those with interest in these matters, (or who can't get to sleep at night) the following go into the problems in detail although things have moved on a little since they were written.

http://www.scssurvey.co.uk/downloads/go5a.pdf
http://www.scssurvey.co.uk/downloads/go6.pdf

The issue with this one was that the pool had been built maybe ten years ago, and at that time had been surveyed to spec (and our survey showed it probably had been surveyed/built pretty good) but in the interim, someone had tiled the ends, the net result being that the tiles "protruded" into the 50m and they were uneven horizontally and vertically. We surveyed it and plotted average lines to bring it back to over 50m including allowance for the pads - from memory there was another issue to accommodate there, that being the compression of the pads when they are triggered, which needs to be taken into account in the length measurement - and then marked those as cut lines on the structure. We had reflector targets on the wall opposite the instrument to check for any issues. We checked the pool dimensions after it was cut back and it was within the tolerances - I think we aimed for 50m +20mm to allow for the pads/compression. This was about 3 years ago. The pool remained filled throughout the surveys and construction work.


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chris mills
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August 14, 2017 2:40 am  

Richard Imrie, post: 441976, member: 11256 wrote: The issue with this one was that the pool had been built maybe ten years ago, and at that time had been surveyed to spec

I'm surprised they didn't empty the pool to carry out the tiling. Must have been interesting (and quite expensive - surely they didn't use the pool while the tiling was going on?)

There is a problem with older pools generally, in that many of them were surveyed before too much thought had been put into the overall interaction of wall tolerance, pad tolerance (and boom tolerance, if you are unfortunate to have one). Now when these are looked at more closely they are often found to be not quite what they were certified as.

Retiling is a common problem, as the original grout doesn't always get cut fully off, so the tiles then protrude. The most common cause of a pool failing on the length is the top nosing tiles, which always seem to ride forward as they are laid. This is more of a problem when there is an end gutter at water level with an upstand for the timing pad extending above. The lower nosings ride forward and then the whole of the upstand tiling is plumbed from that line


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rfc
 rfc
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August 14, 2017 5:03 am  

Astro backsight with 5/8-11/tribrach capability.


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