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.

]]>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?

]]>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.

]]>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.

]]>I hope this helps !]]>

This can be made to work well by using a suitable jig.

I still like my fluid-measuring idea, though (see post #73)......which I've left open as a puzzle to try.

]]>The pipe is bent and will be forever, and for me, atleast, it is very hard to imagine it without a bent

]]>For my technical drawing program I used M$Word. I'd still be drawing it if I tried it in CAD...in which my skills are zero.

bob bundy wrote:

Mrs B wrote:Get a tape measure and measure it.

Bob

That's the best idea yet!

So, measure the whole length of pipe - following the curves - along the line of the inner face of the bend and then along the line of the outer face of the bend, add the two measurements together and divide by two to get the centreline length...which, assuming no compression or stretching occurred along the centreline during the bending process, should be the original pipe length.

The tape must remain in contact with the pipe for the entire length of both measurements, of course.

]]>Wunderbar!

]]>Wow! that's a beautiful diagram. Haven't seen one of that quality since doing A level technical drawing.

So we have a mathematical answer; the practical blacksmith solution and now my wife has offered her solution:

Mrs B wrote:

Get a tape measure and measure it.

Bob

]]>]]>Wunderbar!

Any solution will be imprecise because of the physical measuring required, but the following method may give an answer that is close enough.

The length of the pipe is the length of its centreline, which in the case of a pipe that has one bend comprises three components: the two straight

bits, which are easy and boring to work out, and the curved bit, which is much more interesting and exciting to find.

That centreline arc length can be calculated like this:

r = the radius of the circle that fits in the inner curve of the bend.

d = the pipe's outer diameter.

CLR = r + d/2 (the distance from the circle's centre to the pipe's centreline arc is known in the pipe-bending industry as the 'centreline radius', or 'CLR')

a = the bend angle (ie, the number of degrees by which the two straight sections deviate from each other).

The idea now is to:

- use the CLR to work out the circumference of the full circle that uses the centreline arc;

- then divide that by 360 to obtain the length per degree;

- and then multiply the result by the number of degrees ('a') in the bend angle to find the total length of the centreline arc.

Add the result to the lengths of the two straight sections (s1 and s2) either side of the bend, and we're done.

So, putting all that together into a formula:

]]>You are having LaTeX problems because of '}. See my previous post.

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