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Bill Stanley
Joined: 15 Apr 2004
Posts: 315
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 Posted: Wed Jul 28, 2004 9:07 pm Post subject: Accuracy |
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Accuracy
The great pyramids were built on ground that was prepared to an accuracy of 1 inch in 750 feet.
What precision (Matt likes the alternate word) does your surveyor/landscape preparation crew with their sophisticated laser equipment provide? Why are we not more accurate than construction crews of 4,500 years ago?
The excavator Bubba tells me that he can get the site to within plus or minus one brogan in 100 feet. Bubba is a nice guy but he is blowing smoke up everyone’s dress.
I like accuracy
Bill Stanley |
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Derek
Joined: 13 Apr 2004
Posts: 568
Location: Melbourne, Australia
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| Posted: Thu Jul 29, 2004 1:29 am Post subject: Re: Accuracy |
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| Bill Stanley wrote: | Accuracy...
Why are we not more accurate than construction crews of 4,500 years ago? |
It's all Darwin's fault. He devised the notion that the genes of the weak are naturally weeded out of the gene pool of a species.
The construction managers working for the Pharos didn't believe the process was 'natural' and they took an active role in making the process work:- it was death for anyone that got it wrong.
Today we all sit back in the belief that the ones that get it wrong will be weeded out and therefore the bad practice will not be perpetuated. The reality: too many people just don't care and the sh#t keeps floating to the surface. All hale Pharos Bubba.
D. |
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CJH
Joined: 24 Apr 2004
Posts: 323
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| Posted: Thu Jul 29, 2004 10:00 am Post subject: |
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For most construction, plus or minus 1/4" is about as good as it can be. This is due to any given material is difficult to get better than 1/8" accuracy, and at any given point in a building two inaccuracies may add up.
Foundation slabs are very hard to screed to less than plus or minus 1/8".
Cutting wood to length is always plus or minus 1/16"-saw blade thickness.
So there is the 1/4" minimum. Even if built perfectly, wood floor members can shrink up to 1/4" in 12", and then deflection of beams and joists of 1/4" in 10' is considered acceptable.
Of course, drawing is different. With on Cadd things need to scale within 1/8". |
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JohnMorse
Joined: 14 Apr 2004
Posts: 294
Location: Birmingham, AL
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| Posted: Thu Jul 29, 2004 12:30 pm Post subject: |
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Also, sometimes inaccuracies are in danger of being multiplied many times in one direction. Bad practice, but easy to accomplish in a CAD world of linear multiples, etc.
In our office we always endeavor to draw as accurately as possible to avoid mounting error. Then we try not to dimension to less than 1/4" unless some special condition makes it absolutely necessary.
Of course the man in the field (usually named Mike or Rick for some reason) is going to be using backhoes and variable-width lumber and that old measuring tape with the banged up end cap and half the numbers worn off - but at least we're not TELLING him to do it wrong. |
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