Measure Round With A Straight Ruler
By Benjamen Johnson
Sure, you can use a calculator or even your head to find the circumference of a round duct by measuring its diameter, but with the Cooper Tool Tinner’s Circumference Rule all you need to measure is the diameter — the ruler will read the circumference.
The tempered medium-weight steel rule measures in inches by 1/16″ on the top edge and circumference inches by 1/8″ on the bottom edge. The black markings are easy to read, and on the reverse side Cooper has printed relevant formulas and tables for easy reference.
The rulers come in 3′ and 4′ lengths — both rulers measure 1-1/4″ wide and 1/16″ thick. At $60 on the bottom end these circumference rulers aren’t cheap, so practicing your arithmetic might be a little more cost effective.
Tinner’s Circumference Rule [Cooper Tools]
Street Pricing [Google Products]
Via Amazon [What’s This?]
October 12th, 2009 at 11:37 am
Or you can just get a seamstress tape measure. You can find them for under $10. Luckily my mom has been sowing before I was every born so she had quite a few I could ‘barrow’.
http://www.google.com/products?q=seamstress+tape+measure&hl=en&lnk=pruser&price1=&price2=10
October 12th, 2009 at 12:09 pm
yeah, this is silly.
October 12th, 2009 at 12:09 pm
or use a thread or shoelace, even a strip of paper. yeesh.
October 12th, 2009 at 12:39 pm
2pi*R it’s not that hard i always have a calculator around
October 12th, 2009 at 1:28 pm
Can’t we just use (3 * Dia) and add a little? It is not like you can accurately get down to the 1/8″ when you have a straight ruler measuring a round surface.
(What’s the difference between an engineer and a scientist? To a scientist, pi is 3.14159….. To an engineer, pi is 3.)
October 12th, 2009 at 1:45 pm
ha “(What’s the difference between an engineer and a scientist? To a scientist, pi is 3.14159….. To an engineer, pi is 3.)”
i just use the pi button on my calculator
October 12th, 2009 at 3:56 pm
On a prior ost - I noted:
Wheeler Rex makes a pipe diameter tape:
http://www.wheelerrex.com/catalog/Wheeler_Rex_2009_Catalog_55.htm
My pipe supplier use to give these away as gifts
October 13th, 2009 at 4:21 am
WOW is Pi really that hard
October 13th, 2009 at 6:53 am
i know, it’s completely irrational! lol
October 13th, 2009 at 7:28 am
“i know, it’s completely irrational! lol”
A+!!!!
October 13th, 2009 at 2:08 pm
Fred is apparently the only one of you folks who’s used a pi tape. They’re everywhere in the OCTG world.
http://snipurl.com/shwzu
October 13th, 2009 at 4:05 pm
When I was a lad we just used 22/7, and it’s a pretty useful back-of-the-envelope estimator. I don’t see this kind of ruler as very useful for measuring a duct to determine its circumference– you’d have to have a duct that’s nearly perfectly round, and I see a lot of ductwork that isn’t like that.
If the relationship between the two sets of numbers were reversed, with the circumference marks at full length and the diameter marks at C/pi, you could use the ruler directly to mark a piece of metal for making a cylinder or duct of a given diameter. You’d really only need the C/pi marks. When I used to use a 45 degree ruler a lot, everybody else I knew would pinch the ruler and turn it over to see what the conversion was but I’d just double the offset length I wanted and read the measurement directly off of the offset length side. I always thought they’d be easier for people to use if the relationship between those numbers was reversed, too.
I don’t think I know any engineers that would agree with that “pi is 3″ comment.
October 15th, 2009 at 8:15 am
Actually, every engineer I know would beat you about the head for that “pi is 3″ comment.