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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.
I'm looking for a 50' steel measuring tape with 1/32" increments. I've looked all over online for one but I'm unable to find one. Has anyone had any luck with finding something similar to what I'm looking for?
If you need that kind of accuracy over that distance, you're using the wrong tool........get a laser.
Sounds like you are getting shafts parallel, not 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.
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.
.I'm looking for a 50' steel measuring tape with 1/32" increments. I've looked all over online for one but I'm unable to find one. Has anyone had any luck with finding something similar to what I'm looking for?
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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.
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.
Good idea, I would even add a dial indicator to one end.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.
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