The photos of my brace stick that I posted in May 2012 didn't make the transition to the new site, and I've been asked about them, so I'm appending to this thread.?ÿ The stick began life as a 4-foot length of 1/4"x1-1/2" aluminum bar.
Overall view:
Graduation detail.?ÿ I hand-marked the increments using a regular tape measure, then used a custom-made bit mounted in an arbor press to cut the lines:
Originally I threaded (a little off-center, by accident) a plumb bob point into the end of the bar (that I tapered with a hacksaw).?ÿ This worked fine until a few years ago, but this stick gets a lot of abuse -- e.g., jamming down into drain inlets to measure inverts, stabbing into the ground to free up a hand, digging around for monuments when I forget to bring another tool -- and one day the point snapped off.?ÿ More about that later, but here's what it looked like originally:
I stuck a vinyl tube cap on the top end for comfort.?ÿ It was a little oversize, so I padded the sides out with some strips of rubber.?ÿ It works well:
I had planned on sticking a company label on it so that I might get it returned in the event that I absent-mindedly left it somewhere, but decided to try engraving instead.?ÿ I ground the tip of an old screwdriver into an engraving tool, traced the lettering on, and hacked away.?ÿ The result is a bid crude, but it worked:
Now, about that tip repair.?ÿ The broken-off plumb bob point was too hard to drill out, so I had to cut off the end of the bar.?ÿ That meant that simply drilling and tapping for another plumb bob tip would throw all the graduations off, and the bob tip had proved itself to be vulnerable anyway, so I needed a fix that would be more robust and allow me to retain accurate graduations.?ÿ And I needed it fast.?ÿ I played around with a couple of ideas, and the first one I tried involved the flat blade of a carbide-tipped tile scorer?ÿ However, the blade proved to be too soft and it bent after a day or two of use.?ÿ Going back to the drawing board, I next tried a solution that's been working for some years now:?ÿ I bought a 1/4" carbide-tipped masonry bit, filed a groove for it in the end of the bar and a similar groove in a companion piece of bar, and used a couple of machine screws to clamp everything together.?ÿ It's kind of kludgy and definitely ugly, but I don't worry about breaking the end.?ÿ I was concerned at first that the additional thickness would prevent the end from fitting between drain inlet bars (I dip a lot of DIs), but that hasn't been a problem.?ÿ So far so good!
"I would also, if possible, try to get the backsight closer to you. 400 feet is quite a distance. I don't know the constraints of your site, and it might not be possible, but I think you'll get a better reflected signal, and also perhaps better angle measurements, from a prism that is closer to you. "
Can you explain why??ÿ I think the longer the backsight, the better, within reason.?ÿ His Leica 1203 EDM has a single prism range of 6,000' even in hazy atmospheric conditions?ÿ so surely a 400' shot is getting a "very good" reflected signal.?ÿ Concerning pointing accuracy, as long as the target is larger than the crosshair, the instrument's accuracy is 3-5", and atmospherics aren't in play, further away is better.?ÿ?ÿ
A thought experiment:?ÿ Consider two backsights, prisms on tripods, one is 100' distant and the other is a mile distant. A mule rubs on the backsight tripods and knocks them laterally 0.05'.?ÿ The 100' backsight's azimuth is now off by about 1 3/4 minute, the mile backsight is off by 2"+-, (about the instrument's pointing precision).?ÿ Turn the angle to set a precise location onsite that's 500' distant and the short backsight sets it wrong by?ÿ 0.25', using the long backsight it's off by 0.01' theoretically, given budget errors more like 0.03'+- real world.
Long ago I did bridge construction surveys where tolerances are critical (prestressed beam & steel) and always set a tight control network which included several centerline alignment control stations far from the worksite (a thousand feet out of the construction zone up on the hillsides) precisely so if day to day site control went to sh*t because of earthwork, lousy unstable formwork and/or mother nature I'd always have a solid foundation to prove my work.?ÿ The beancounters hated it but one time a pier was 0.50' out of alignment and the lawsuit lawyers came out in force claiming bad construction staking and I was able to prove through fieldnotes that the pier control stakes were spot on during concrete placement (destroyed by the contractor soon after the forms began distorting) thanks to my backsights 1,000 feet offsite.
Geodetic surveying, meh, a lot of tricky deflection of the vertical, geoidal undulations, orthometric corrections, GPS considerations, a mind twister.?ÿ But, when delivering precise construction deliverables who cares about precise LAT-LON, true vertical datum, etc.?ÿ When building an expensive big thing it's all local coordinates, and you'd better have your ducks in a row down to +-0.05' site wide *and* have the indestructible monuments offsite to prove all your onsite staking.
