Large Diameter Pi Tapes

I am wondering if anyone knows where I can find a Pi tape that can measure a 18' diameter and also 16'-3" diameter. Any help is appreciated.

Thanks

Bah, just use a piece of banding strap and a little math. If you're producing the same diameters, then you can put a mark at nominal and two marks on either side of your tolerance for fast, mistake free QA.

A measuring tape and any el cheapo $2 calculator.

- Leigh

Why, from Pitape.com!

http://www.pitape.com/products-extendedrange.htm

It looks like the .001 stop at 12' diameter. For 12'-18' they only read to .010.

Pi tapes and large diameters

"For 12'-18' they only read to .010"

thats because a pi tape that big stretches and is also hard to hold it square. if held at a slight angle it will read a larger diameter than it is actually.

pi tapes are rated to dimension with a certain pull or tension at a rated temperature (usually 20 degrees Celsius)

When doing large scale straight measurement with metal tapes you often need 4 people.
1) to hold one end
1) to pull with a spring scale
1) to use magnifying glass on zero end of tape measure
1) to use magnifying glass (or headband magnifier or microscope/telescope) to read tape measure
verbal communication that zero end is "good", spring scale is "good" then reading is recorded. also the tape measure support that is continuous or 2 or 3 or 4 point support will give different readings. We use a calibrated tape measure that came with a 100 page computer printout showing how tape measure will change reading depending how it is supported.

Large scale measurement repeatability is not as easy as it appears.

Pi tapes are pretty much self-centering if you slip it sideways each direction a few times while holdng teension. I used to tape it to the work at several points around the circumference for support with bandaids so the tape was free to move under the gauze part.

I have a whole set of pi tapes from 2 ft to 12 ft somewhere in my stuff.