Author Topic: Pretty accurate long tape rule  (Read 214 times)

Offline PekkaNF

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Pretty accurate long tape rule
« on: October 04, 2018, 03:26:34 PM »
Long story short: Need some information about 15 m long tape rule that is very much more accurate than the ones used in building industry.

Least 20 years ago the crew has left the project and we had to check some alligments. No theodolite or such, one old hand had a german tape tule that needed 50 N weight to stetch with correct force and I think we used it to measure pretty small difference in 15 mm loop (or circumfrence).

Now we have some customers that don't have access to optical measurement system and they wold like to use tape and/or lines to identify problem to some extent without resorting to outsourcing the measuremet (with couple of days to wait and serious money).

My concern is not absolute accuracy, but comparision and repeatibility. Would like to measure realiably 1-2 mm difference in half an hour time span, make multiple measurement and notice a difference that might be close to uncertainty of the tape properties.

Only document I could find was about survey. Sort of right stuff, but wrong scale.

Any ideas where to find info an maybe to find a tape just to try out and satisfy my curiocity.

Also if there is manufacturer for modern accurate steel tapes that can be used to check alingments mechanical parts, when optical measurements are not an option.

Thank you,

Offline hanermo

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Re: Pretty accurate long tape rule
« Reply #1 on: October 15, 2018, 11:37:19 AM »
Pekka .. if a comparison / reference is the main concern, any steel tape measure should serve.
So should a dti on a rigid rod, or ladder, etc.
As long as the temp is similar, the accuracy in repeatability must be there.

Google pi tape.

A port crane lifting containers, 70 m long, twists about 15 cm in x due to sunlight.

About 3C/micron/inch in D in steel iirc.
So about 40 microns error / m in length for 3C temp difference.

The better consumer laser length measuring tools are about 3 mm iirc in accuracy on 15 m construction-type sizes.
But they might repeat to a lot better.
And they are under 100.

You could rent one from a tool rental place maybe ?
Insert playing cards as shims and watch results ?
Does it repeat if a deck of cards is used as a gage ?

No idea, but in theory they should be very consistent.

The chicom cheap 1u micrometers for 20 are crap.
I tried 4.
The good ones are excellent, around 50 retail.
Similar should apply to the laser rangefinders.

The proper ones using interferometrics used to be 30k$ or so a few years back.
I suspect the prices on these will collapse similar to servo/stepper drivers and gps chips.

Offline PekkaNF

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Re: Pretty accurate long tape rule
« Reply #2 on: October 15, 2018, 01:13:09 PM »
Thank you.

This is exactly what I was lookng for, but least 10m long, ideal is about 15 m. I ahve seen one german made and one american made. Can't rememeber brand though. Like this, but longer:

This is a little special...lets't say there are many rolls like in a web processing machine and there are many rolls that only few are in a straight line of sight.

Obivious choice would be the use of tacheometer or theodolite and prism and and all sorts of stcks to bring the reference to line of sight.

Not everybody has the equipment and personnel to use optical measurement and stick micrometer bends badly around concrete and steel beams. But because material web makes it trought the mace, tape would be pretty intitive and to go same route.