Pi Tape

[rake60]

When I was operating a large vertical boring mill at work, it wasn't uncommon
to machine parts up that were over 100" in diameter. To accurately measure
machined fits on parts of that size we used Pi Tapes.
They work just as well and accurately on small parts.

The tape is wrapped around the OD of the part and as it overlaps it's self
scribed lines on the tape are lined up and read just as a scale on a vernier caliper,
converting a circumference measurement into a diameter measurement.

This is a picture of one of my .75 to 7" tapes measuring the OD of a piece of
1-3/4" brass stock.

While the 1" mark is not visible in the picture the 7 graduations and vernier scale
are clearly visible. The 0 on the vernier scale is lined up perfectly with the second
mark on the tape. Each graduation on the tape is .025" SO the tape is reading the
diameter as 1.750"

OK I don't know how well I explained all that, but a Pi Tape is an accurate item that
can replace a set of micrometers for OD measuring. The .75 to 7" version that I own
can be found on Enco's web site at Pi Tape

Rick

 

[Hexbasher]

eeek those are a bit pricey

i think i'd rather deal with nightmare that is known as micing with the 18inch multi anvil mic


then again, i'd only use that tape to use with a mic to double check (currently, for over 12 dia, i use both the shops 24in vernier and the appropriate mic.) 80% of what i turn at work has a 0.0005 tol somewhere,which that tape doesn't help me with...and does nothing for measuring out of rough

neat though

 

[rake60]

tattooed-machinist

If the shop you work for owns a Pi Tape give it a try some day.
I'm sure you will be impressed with it's accuracy when compairing it to mics.
I have been using them for 18 years at the shop I work for and have never
doubted a reading.

As for their price, I bought the two I have at home from an eBay auction for
a total price of $27 including shipping.

Rick

 

[ed miles]

Rick, we have a use for this on diameters 12" to 25" which does not justify the purchase of outside micrometers since they only check about twenty per year. This system would be perfect for the application. What brand name do you have these tools so we can get a price on a new tool. The application is industrial so we do not want to spend time on EBay to find one.

Ed

 

[rake60]

Ed
Most industrial suppliers carry Pi Tapes.

My small .75 to 7" is kind of an oddity to them, as most go in 12" increments.
ie: 12 to 24", 24 to 36" ect.

MSC carries all of them. Here a link to the 12 to 24" Pi Tape

Rick

 

[wareagle]

That is a handy looking item to have in the arsenal. I may have to keep my eye out for one as they look pricey at MSC.

 

[greenie]

Yep, they work a treat allright, but don't do what I did, it caused the boss to have a dummy spit.

Using the tape as the work piece in the chuck was rather large, I had to stand up on the edge of the lathe bed to get the tape around the item, took the reading and released the tape, stepped back down from the lathe bed and right onto the tape which was laying on the floor. It just so happened to be edge UP and my great clod hopper, just snapped it like a small branch.
Ah well, now had two tapes, a real short one and a bloody long useless one.

Lesson learned, look behind before stepping back ! ! !

regards radish

 

[ed miles]

Rick, they used to use a Pi tape to match new railway wheels on an axle at one time. The wheels are turned on a vertical lathe, measured, marked and then stored by the wheel press for assembly onto the axle. That was back in the 60's, so that may have changed by now. Forgot about that one since it was so long ago. Thanks for the reminder. We will try one out in the New Year to see how it works for us and let you know the results.

Have a Merry Christmas & a Happy New Year

Ed

 

[bob ward]

A small version of the Pi tape was standard equipment for most garages, going back a few years. It was used to check piston ring sizes.

 

[rake60]

The Pi Tape as we know it today was invented just after WW2

I know I'm a little odd here, but I enjoy tool history. LOL
Here's a link to the Pi Tape web site: A Brief History of Pi Tape

I have no affiliation with the company. Just a very satisfied user of
their product.

Rick