permaculture

["Gene Monaco" <efmonaco@comcast.net>]

This one got me thinking.
A typical engineers scale of 20, 30, 40, 50 or 60 divisions to the inch can
be thought of like this.  Take the 20 scale for example.  
This is typically used as 1 inch = 20 feet.  
Since there are 12 inches to the foot that would be: 

  1/12 foot = 20 feet.  

Multiply both sides of the equation by 12 and you get:

  1 foot = 20 x 12 = 240 feet

This is a ratio of 1:240

For any of the other standard engineering scales simply multiply the scale
divisions by 12 to get the ratio of the scale:

10 scale = 10 x 12 = 120 ==> 1:120
20 scale = 20 x 12 = 240 ==> 1:240
30 scale = 30 x 12 = 360 ==> 1:360
40 scale = 40 x 12 = 480 ==> 1:480
50 scale = 50 x 12 = 600 ==> 1:600
60 scale = 60 x 12 = 720 ==> 1:720

The bad news is that none of these is in the ratios of 1:100, 1:125, 1:250
and 1:500 that Rafter was looking for.  The same thing holds with architects
scales:

    3" scale:     3" = 1'0 ==>  1/3 x 12  ==> 1:4
1-1/2" scale: 1-1/2" = 1'0 ==>  3/2 x 12  ==> 1:8

  3/4" scale:   3/4" = 1'0 ==>  4/3 x 12  ==> 1:16
  3/8" scale:   3/8" = 1'0 ==>  8/3 x 12  ==> 1:32

  1/2" scale:   1/2" = 1'0 ==>    2 x 12  ==> 1:24
  1/4" scale:   1/4" = 1'0 ==>    4 x 12  ==> 1:48

  1/8" scale:   1/8" = 1'0 ==>    8 x 12  ==> 1:96
 1/16" scale:  1/16" = 1'  ==>   16 x 12  ==> 1:192

One thing good about all this is that if you are ever using USGS Quad
sheets, the scale is 1:24,000, which means 1'=24,000' or 1"= 24,000" or 1
meter = 24,000 meters.  Whatever you want.
So you can use either the 1/2" Architects scale or the Engineers 20 scale
because they are in the ratio of 1:240 and then add the right number of
zeros like you did when they explained the slide rule in 5th grade (if
you're my age). 

However, with Architects scales, if you think only in inches, then a 1/4
scale has 4 divisions per inch, which is a ratio of 1:4 which is equivalent
to 0.25:1.  Multiply your 0.25 x 1000 and voila, you have 250.
So if you wanted to lay out 1000 feet on a drawing at a scale of 1:250, you
could use the 1/4" scale.  Draw a line 4 inches long and think of it as 1
inch = 250 feet.  For the others use 1/8" scale for the 1:125; 1/2" scale
for 1:500; and 1" for 1:100.

Yes, this is convoluted as hell and nobody would ever do it that way, so
from this I would have to conclude that Robyn must be right; however, I do
not see any of these scales in metric on the draftingsteals.com website, so
Vint, what am I missing?

Gene Monaco

--------------------------------

>From: Robyn Francis <erda@nor.com.au>
Subject: Re: [permaculture] four-bevel surveyor's scale - anyone?

The scale ruler recommended is a metric scale ruler.
I think in the US the standard engineering scale ruler is 1/10th inch. From
there it gets too complicated for me to explain simply by email...
Ciao
Robyn



On 4/12/09 7:26 AM, "rafter sass" <rafter@liberationecology.org> wrote:

> Hey folks,
> 
> Does anyone know a source for a  4-bevel flat surveyor's scale?
> I'm following up on one of Darren Doherty's recommendations for a 
> field kit:
> 
> Scale Ruler - Flat Four Scale - 1:100, 1:125, 1:250, 1:500
> 
> I've searched high and low, and the scales I find that have anything 
> like those scale ratios are triangular (and therefore a pain to carry 
> around in the field), while the flat four-bevel scales that I find are 
> for engineers and/or architects - not surveyors - and thus have 
> different scale ratio systems.
> 
> Darren? Anybody?
> 
> Thanks!
> 
> Best,
> Rafter
>