18" sonotube actually 19" in diameter???

Discussion in 'Archived Threads 2001-2004' started by Mike Dr, Feb 25, 2002.

1. Mike Dr Stunt Coordinator

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I just got the sonotube (finally).. the place didn't have 20" so I went with 18" ... in any case, I just measured it and it seems the outside diameter is 19" and the inside diameter is about 18 5/8" .. anyone else see this trend?

the tube brand is "easy-pour"

thanks

2. Harry Lincoln Stunt Coordinator

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Mike, the tubes are usually measured by their inside diameter, you'll probably find that the tube was slightly out of round when you took the 18 5/8" measurement, if you were to take another measurement 90 degrees from the first i'm guessing that you would get about 17 3/8". When the endcaps are added the tube should be perfectly round.

Harry.

3. Dustin B Producer

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That is what I found with my 18" sonotube as well. The inner radius was 9 6/16".

Without some method to determine the exact centre and keep the tube perfectly round I wouldn't try and directly measure the diameter. I used the following method:

First I used the method on Patrick Sun's web site to square up one of the ends of the tube. I place this square edge on a flat surface. I take something like a nylon tie down strap (the kind that are like a ribbon that is just under an inch wide) and wrap it tightly around the tube and push it down so that it is touching the flat surface all the way around. I mark this distance on the strap. Then I straighten out the strap and get my circumfrence measurement.

Then I use C/2pi = r to get the radius. This is the outer radius whether the tube is a perfect circle or not. Then I take some callipers and measure how thick the tube is. Take this off the radius you got from C and you have the inner radius.

Even with this, I still made my first cut to the endcap too big, and slowly cut it down until it fit.

4. Mike Dr Stunt Coordinator

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Well, just to be sure, I just measured it from all sides and took some pics. Take a look. All the measurements are within 1/4" of each other.

edit:
I just used Dustin's method and I come up with 18.9" as the inside diameter (60.25" circumference, average .17" thickness)

5. Brian E Screenwriter

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Never mind.

6. Mike Dr Stunt Coordinator

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?????

7. Kevin Liedtke Agent

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The sonotub that I got was not perfectly round when I did initial measurements and I cut them to what the tape said. But when it came time for the placement, they were approximately an inch off. But if you are in doubt, cut it big, it is much cheaper to trim down than to have make new circles.