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Tape measure
- Thread starter ksulogan
- Start date
- Replies 27
- Views 3,772
Ken hosford
Cast Iron
- Joined
- Oct 29, 2005
- Location
- dexter mich
Not surprised I feel I can read a 1/16" tape to well better than 1/32" A 1/32" is half way between the 1/16" marks even with my 62 year old eyes that's no big deal the marks are close to 1/64" wide on 50 ft your sag in the tape is going to be a bigger issues than the resolution .
cellardoor7
Cast Iron
- Joined
- May 23, 2010
- Location
- NY USA
On a 50' tape, the 1/16th marks are a waste of ink.
Gordon Heaton
Titanium
- Joined
- Feb 19, 2007
- Location
- St. George, Utah
When you get to the end you want to read, just hold a small scale in line with the relevant 'inch' on the tape and read finer grads on the scale.
Jim Williams
Stainless
- Joined
- Oct 3, 2002
- Location
- Grant, Florida
Cellardoor7 is telling it like it is. Look up the coefficient of expansion of steel and calculate the change in tape length per degree of temperature change. You can not measure to that kind of absolute accuracy with the tape wandering all over the place. Bridges have significant expansion gaps built in to handle he problem of thermal expansion. You could determine at what temperature the tape is fifty feet and calculate where it is at your using temperature. You could then use a correction factor to apply to your 1/32 readings and maybe get a little closer. If you wanted to refine your measurement, you could calculate the amount of tape stretch at the tension you are using. I admit to being a bit tongue in cheek with this discussion. I wanted to demonstrate how materials move around under physical influences. The manufacturers do not use 1/32 marks on a 50 foot tape because it is fantasy to consider using such a marking effectively.
dgfoster
Diamond
- Joined
- Jun 14, 2008
- Location
- Bellingham, WA
The 50 foot tape changes length by .0036 per degree F change. IF the tapes were accurately printed at a controlled 72 degree temp and carefully compensated for temperature, thermal expansion itself is not a deal breaker. But your average 50 foot tape is probably loosely printed at whatever temp the plant was that day....
Denis
steve-l
Titanium
- Joined
- Mar 2, 2012
- Location
- Geilenkirchen, Germany
If you need that kind of accuracy over that distance, you're using the wrong tool........get a laser.
Gordon Heaton
Titanium
- Joined
- Feb 19, 2007
- Location
- St. George, Utah
It doesn't matter much how accurate the tape is if the same tape is used to measure & fabricate all the stuff that goes together.
wheels17
Stainless
- Joined
- May 10, 2012
- Location
- Pittsford, NY
The laser is a good suggestion. I just had a survey done Wednesday, and the surveyor was using a laser that was at least 10 years old. That one has resolution specifications of about 2 arc seconds in rotation about the horizontal and vertical axis, and 1/1000 of a foot (.012 inches) for distances up to 1000 feet. I'me sure the current generations are even better.
I have a 7 year old Leica Disto 330i laser measuring instrument that's rated +/- 1mm over 100 meters and it really seems to deliver that accuracy. Ken H's comment about the sag is very true.
The new $99 list disto D1 is rated at +/- 2mm at 120' under "favorable" conditions.
$200 gets you 1.5mm out to 100m
$329 gets you 1mm out to 150m
Not associated with Leica, just like the product.
I have a 7 year old Leica Disto 330i laser measuring instrument that's rated +/- 1mm over 100 meters and it really seems to deliver that accuracy. Ken H's comment about the sag is very true.
The new $99 list disto D1 is rated at +/- 2mm at 120' under "favorable" conditions.
$200 gets you 1.5mm out to 100m
$329 gets you 1mm out to 150m
Not associated with Leica, just like the product.
I'm using this in an applications where I'm measuring from a shaft (diameter) to another one to square one piece of equipment up with another and getting it within 1/32 of square
I would love to be able to use a laser for the application im using this for, but its not going to accurate. I'm measure squaring two shafts up to on another over a 12 foot distance. So I'm wrapping the tape around one shaft and back around the other and getting them under a 1/32 of squareness to on another.
Rob F.
Diamond
- Joined
- Aug 5, 2012
- Location
- California, Central Coast
Sounds like you are getting shafts parallel, not square.
My brain feels fuzzy now. You are "wrapping" a Measuring tape "around" shafts? And you are expecting to be accurate, or at least comparable within 1/32", with this method?
I think you need a 50' Tailors measuring tape
, or anything that will give you a comparable measurement, it doesn't even need to be a measuring tool. Were it me, I might use a Steel Pi tape?DMF_TomB
Diamond
- Joined
- Dec 13, 2008
- Location
- Rochester, NY, USA
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i used to use a Invar metal tape measure in 1/1000 of a foot or .0125" increments.
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$30,000 invar tape measure and guaranteed to not change length with temperature at least in extremely small amounts. came with NIST calibration report based of how supported
held on ends
held on 3 points
hold on 4 points
continuous support
the error compensation table would list reading to adjust the tape read measurement with tape stretched with 10 lbs tension
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takes 4 guys to use, 1 to hold one end and adjust left or right, 2nd to pull with 10lbs scale, 3rd guy read zero end with magnifying glass or glasses, 4th guy looking through optical transit or theodolite at 30x magnification. usually got repeatable readings to about .010" seen with transit BUT
BUT
.....the problem with a tape measure that does not change length with temperature is most things you measure like steel and concrete DO change length with temperature. thus if building is experiencing temperature changes you could easily read .020" or more difference in the afternoon compared to the morning.
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it actually gives more repeatable reading using a steel tape measure not a invar tape measure but still need 4 guys, a spring scale, magnifying glass and a optical transit or magnifing glass for the other end and must support tape measure the same way each time measured with same spring tension force
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by the way laser inferometer to measure length needs stable air temperature. if you ever looked through a optical level at target 50 feet away with a heater in the area you often can see the target appear to move with the air shimmering . like looking down a highway on a hot day. i have seen laser level readings change easily over 0.25" just by turning a heater off.
Ron Hofer
Hot Rolled
- Joined
- Jul 7, 2007
- Location
- Brookfield, WI
I agree with RobF, sounds like making them parallel to me. Why not just make a "stick" gage of the right length to stick between the two shafts? Could be a piece of aluminum extrusion, of size to match up to the shaft diameters, cut it to the length needed, and just move it back and forth while tapping the shafts (or motors, or whatever it is) into parallel relationship. Maybe a piece of aluminum bar about 1/2' x 1" on edge. Might require a helper.
The slick way to align them dead-nuts would be with an alignment telescope and appropriate right-angle mirrors to clamp on the shafts.
Rob F.
Diamond
- Joined
- Aug 5, 2012
- Location
- California, Central Coast
Good idea, I would even add a dial indicator to one end.
If you need that kind of accuracy a stick micrometer is what you need, not a tape, I have a mitutoyo that with extra sticks (350 mm is the size I have but they come in bigger sizes) can reach 12’, when going longer I use a length of hydraulic tube and stick the mic in, usually your comparing the distance at several points anyway,
Mark
Mark
DMF_TomB
Diamond
- Joined
- Dec 13, 2008
- Location
- Rochester, NY, USA
tape measure often used for floor points on a big machine alignment. basically a hex bolt head sanded smooth epoxied into hole in concrete hole 50 feet apart with a center punch mark on it.
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sure 50 foot trammel gage can be used but not practical at those distances. a needle sitting in center punch mark is seen with optical equipment for alignment purposes.
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2 rows or lines of floor points 50 feet apart. measured to confirm parallel or equal distances apart
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sure 50 foot trammel gage can be used but not practical at those distances. a needle sitting in center punch mark is seen with optical equipment for alignment purposes.
.
2 rows or lines of floor points 50 feet apart. measured to confirm parallel or equal distances apart
