Math Is Fun Forum
You are not logged in.
- Topics: Active | Unanswered
#101 2013-11-28 17:51:43
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,879
Re: Measure length without bend ?
Hi SuperLynx,
It looks to me like you've drawn a circle whose diameter (15.85) is simply the straight-line distance between the inner ends of the two red lines, and if so, we're still missing some vital info for calculating the pipe length.
AFAICWOFWIRATOTI, the length of a pipe with a single bend is the sum of the lengths of the two straight sections either side of the bend, plus the length of the arc along the pipe's centreline that joins the two straight sections...and the diameter measurement in your drawing isn't the right one for working out that arc length.
Are you trying to use the circle idea that I described in my posts #92 and #93, in which I show how to find the length of the arc? If so, then I think you've misinterpreted what I said. My method in those posts is adapted from information that I obtained from several websites to do with pipe-bending, and, provided that I interpreted their drawings and notes correctly, you'll need to follow the instructions in my posts exactly in order to find a solution to your problem with my method.
I think that the simplest method for you, with reasonable accuracy (but possibly not as accurate as you need), may be the one in post #97.
Last edited by phrontister (2013-11-29 13:34:56)
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#102 2013-11-30 00:34:05
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,879
Re: Measure length without bend ?
I've just had a thought: that the formula and drawing in my posts #92 & #93 only work for a circular arc (ie, one with a consistent radius) but not for something else (eg, an elliptical arc or a compound arc, both of which have multiple radii)...and we don't know the exact form of the bend.
The method in post #97 doesn't require a radius measurement and will work for various shapes, and so I used it in a practical test on a 3/4" pipe in which I incorporated an elliptical bend, with the following results:
Original straight length = 1000mm
Then I bent the pipe...
Length of inner-curve face ("I") = 984mm
Length of outer-curve face ("O") = 1016mm
Pipe length = Centreline length = (I+O)/2 = (984+1016)/2 = 1000mm
That looks like a good accurate result, but it's only a rounded-integer one, which is about as accurate as I could get with my tape measure.
I also used the fluid-measuring idea on the bent pipe, and got a straight-length measurement of 998mm. 
Last edited by phrontister (2013-11-30 14:39:31)
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline
#103 2014-01-30 14:00:19
Re: Measure length without bend ?
I also used the fluid-measuring idea on the bent pipe, and got a straight-length measurement of 998mm.
Where did you get such a pipe from?
'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'
'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'
I'm not crazy, my mother had me tested.
Offline
#104 2014-01-30 14:17:08
- phrontister
- Real Member
- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,879
Re: Measure length without bend ?
Where did you get such a pipe from?
It was a bit of spare pipe I had laying around in the shed at home, doing nothing but waiting for just such a use as this.
"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson
Offline