I was reading in my book from Lowes. "The Ultimate Guide to Barns, Sheds, and Outbuildings" that you can use a transit to get all 4 corners perfectly squared. Sounds pretty quick and easy. Haven't read anything on here about using the transit though. Anyone use this method?
Been thinking about how I'd use my transit to set the corner posts square and I guess I could do it. But I'd still double check by measuiring diagonals or using a 3x4x5 setup. The only measurement I'd trust is a good tape. What was the transit method outlined in the book?
To lay out four cornders of a building, attach a plumb bob under the tripod head, and set the transit directly over where you have set your first corner. Sight the transit along a string (after unlocking the vertical pivot screw) until the string is lined up in the scope's crosshairs. Set the horizontal scale to 0, and then rotate the scope to exactly 90 degrees. Have a helper place a batter board along where you've sighted, and mark exactly on the board where crosshairs line up. This creates a line at an exact right angle to the string line you first sighted. From this perfect corner, you can lay out the remaining two sides of the building by measuring them. In the end, all four angles will be exactly 90 degrees.
I would also double check with the 3,4,5 also. Sounds like using the transit would be quick though. I have never used on though so you tell me if doing this method would be fast.
I'd do it a little different cause you want remote points so you can reestablish the exact corner.
Assuming one has knowledge one how to operate a transit. [I've forgotten]
Start on site by measuring the proper distance and setting in pins or reference points. Call them point A and B
Set up on B, backsight on A and turn 90 degrees and measure distance to the next corner called C. Have board set up well behind C and make the 90 degree angle.
Set up on C, backsite on B, turn 90 degrees , measure the distance A to B from point C and set point D. Mark board well behind D.
Set up on D, backsite on C, turn 90 degrees and measure distance A to B. It should fall on the point A. Mark point on a board well behind A.
Continue till you have two boards well behind each corner that are marked. Later, when points A,B,C,D are lost just run string lines from the marked points on the boards and they will intersect over the four corners. [img]/forums/images/icons/grin.gif[/img]
If you want to get fussy turn 90 degrees and mark. Then turn 270 degrees and mark. If the points do not coincide check transit level etc and repeat. If they still do not coincide split the difference or get another transit or sit in the shade and enjoy a cool drink till they are close enough! [img]/forums/images/icons/grin.gif[/img]
Or turn 90 degrees and mark, invert transit and turn 90 degrees again. Points should coincide. If not split difference. [img]/forums/images/icons/grin.gif[/img]
Yeah, that would give you a square corner to "some tolerance". The term "exactly 90 degrees" is the caveat. Using that method, I've used my transit to determine a survey stake location that had been moved by a neighbor (long story). I then had it verified by a licensed surveyor and I was within a couple of inches of where they set it. I've also laid out rough building corners on batter boards for sitework using a transit (similar technique as you and Egon describe). When checking against diagonals, invariably 1 (or 2) of the strings must be moved on the batter boards by a small amount. As Egon indicates, it's an iterative process.
Variability comes from the resolution of the transit (expensive vs cheap) and how well you can set them as opposed to someone else, (operator variation) and the distance over which the measurement is taken (1% error at a longer distance may be significant to your project).
But, to answer your question, yeah, it's pretty fast and I would certainly have mine setup when erecting the framework of a building, then check as previously described. I'm a big proponent of "measure twice, cut once" so I tend to double-check & triple-check everything.
(It's better than using a carpenter's square to check the 90 degree angle. A 1/16" error along the 2' length of a carpenter's square will extrapolate to an error of 1.25" error along a 40 ft wall.)
Also, I only trust a 3x4x5 for "final" verification on "hard" surfaces (like a roof or floor) where the legs of the measurement don't move (i.e. string) and you can make solid clean marks. But it's ok to determine where to set the batter boards using string.
Well there are other methods. [img]/forums/images/icons/smile.gif[/img]
Just stand on pin at right angles to the other pin. Point one hand at the pin, point the other hand exactly opposite and then bring your hands together pointing straight in front of you. Have someone set the pin and then measure for distance and off you go to the new pin. [img]/forums/images/icons/crazy.gif[/img] and repeat the procedure.
That system should get you an accuracy of a degree or so. [img]/forums/images/icons/grin.gif[/img]
No sense overdoing things and try for tenths of a second! [img]/forums/images/icons/wink.gif[/img]
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