what's with all the cheap measuring tapes?

[wagin]

Originally Posted by patrickp

if i'm working with specified dimensions then i use a steel rule to get accurate results. otherwise i use the same tape measure through the whole project. and as you stated, if it's not accurate then depending on what your doing you just compound the problem and the results will be way off.

Agreed, I use a steel rule for projects 2' or under. And again, I have encountered discrepancies between cheaper rules. What about projects 2' and longer?

[lugweld]

Having come from managing a farm with research related work involved, and having to have our measuring equipment certified, differences in tape measures may vary as much as 10 percent depending upon temperatures. A hot tape will measure longer than a cold. A cold tape may actually measure shorter than the true length. All certifications must be done at equal and controlled conditions. A tape measure worn on a warm hip, under a jacket or in the pocket will measure different than one left outside in a cold tool box.

[denrep]

Originally Posted by lugweld

...differences in tape measures may vary as much as 10 percent depending upon temperatures. A hot tape will measure longer than a cold. A cold tape may actually measure shorter than the true length....

10 percent? Even with a high quality tape?
Attachment 25888
No wonder I have so much trouble getting it right!

[lugweld]

Vic's Secret ehh? Sounds like you tape may only have 42 inches or so.Those things are never right. Just ask the sixty percent of women who are wearing the wrong (too small) size. Maybe its because 60 percent of women can't read a tape, and just as many men can't either.

[Sandy]

Originally Posted by denrep

10 percent? Even with a high quality tape?

No wonder I have so much trouble getting it right!

We need more info before giving usefull answer.

1) what you were measuring, was it hot or cold?

2) were your hands (and the tape) hot or cold?

3) what you were ordering, who was going to wear it, you or another person??

[denrep]

Originally Posted by Sandy

We need more info before giving usefull answer.

1) what you were measuring, was it hot or cold?

2) were your hands (and the tape) hot or cold? ...

Sandy, So what you're saying is that it would be best to equalize all temperatures before measuring?

[Static-XJ]

Originally Posted by lugweld

Having come from managing a farm with research related work involved, and having to have our measuring equipment certified, differences in tape measures may vary as much as 10 percent depending upon temperatures. A hot tape will measure longer than a cold. A cold tape may actually measure shorter than the true length. All certifications must be done at equal and controlled conditions. A tape measure worn on a warm hip, under a jacket or in the pocket will measure different than one left outside in a cold tool box.

10% is an awful lot. Two and a half feet of variance in a 25' tape at different temps?

[Sandy]

Originally Posted by denrep

Sandy, So what you're saying is that it would be best to equalize all temperatures before measuring?

Definitely!!!

[steve45]

We used 100' temperature compensated steel tapes where I used to work. We would use these to place megnetic marks on wireline cable, which was used to make measurements in oil wells. The magnetic marks were place at 100' intervals, and cable rolled over a calibrated wheel to measure how deep we were in a well. Every 100 feet, we would correct the readings from the wheel and the magnetic marks to insure accuracy. Cables were re-marked every month to correct for stretch, and after every use for the first 6-8 times a new cable was used. We claimed 1 foot in 10,000 accuracy.

Once, I had to go out and run tests on a well that had previously been logged down to 14,000 feet. The customer wouldn't let me see the original test in order to 'get on depth' with it, he made me go with my 'raw' measurement to check our accuracy. I was within 6" with the original run at 14,000'. Even I was impressed.

By the way, the temperature compensated tape had several zero marks on it, for various temperatures. Of course, the correction only applied to a full 100 feet of measurement.

[duaneb55]

Originally Posted by steve45

We used 100' temperature compensated steel tapes where I used to work. We would use these to place megnetic marks on wireline cable, which was used to make measurements in oil wells. The magnetic marks were place at 100' intervals, and cable rolled over a calibrated wheel to measure how deep we were in a well. Every 100 feet, we would correct the readings from the wheel and the magnetic marks to insure accuracy. Cables were re-marked every month to correct for stretch, and after every use for the first 6-8 times a new cable was used. We claimed 1 foot in 10,000 accuracy.

Once, I had to go out and run tests on a well that had previously been logged down to 14,000 feet. The customer wouldn't let me see the original test in order to 'get on depth' with it, he made me go with my 'raw' measurement to check our accuracy. I was within 6" with the original run at 14,000'. Even I was impressed.

By the way, the temperature compensated tape had several zero marks on it, for various temperatures. Of course, the correction only applied to a full 100 feet of measurement.

Wow. Cool stuff. Whoda thunk?

[TSOR]

Originally Posted by lugweld

Having come from managing a farm with research related work involved, and having to have our measuring equipment certified, differences in tape measures may vary as much as 10 percent depending upon temperatures. A hot tape will measure longer than a cold. A cold tape may actually measure shorter than the true length. All certifications must be done at equal and controlled conditions. A tape measure worn on a warm hip, under a jacket or in the pocket will measure different than one left outside in a cold tool box.

10% !!!


I am calling BS on that one.

Maybe 1% in 100ft for fiberglass tapes. Likely closer to .1% in 100ft for steel.

In my experience, not enough to really matter for most things you would measure with a tape.

[lugweld]

According to the manufacturer's certification. Not mine.

[farmersamm]

Tried tellin' her it was 10% longer on a really hot day

[awright]

The linear coefficient of thermal expansion for steel is 10.8x 10^--6/degree Kelvin at 20 degrees Celsius (room temp). (Degrees Kelvin are identical to degrees Celsius except the reference level is absolute zero, or −273.15° Celsius, which is immaterial to this calculation.

For, say, a 40 degree F (67degrees F to 107 degrees F) temperature change, a 100 foot steel tape will expand 100X12X40X(5/9)X10.8X10^-6, or 0.288 inches.

It's up to you to decide whethar that makes any difference in whatever you are fabricating on a hot day.

awright

[steve45]

Originally Posted by lugweld

A hot tape will measure longer than a cold. A cold tape may actually measure shorter than the true length.

Nope, that's backwards. A hot tape will be longer than standard, but the measurement you read from it will be shorter. Likewise, a cold tape will be shorter than standard, resulting in a longer measurement.

[pilebuck]

If im working over the water I use a kinda ****ty tape, in the water a really ****ty disposable tape. Same thing in mud, cleaning em w/ wd40 really doesnt work that well. For fab work most of the time I just carry a 10 or 12' stanley because they fit nice in a pocket and I hate wearing bags. For I beams and cans a self retracting loggers tape is handy. But as long as the same tape is used for layout as for measuring the whatever It dosent matter. For critical stuff over big distances I make the surveyors do there job, set up a transit or a total station. I did a job one time where the surveyors used a gps device instead of line of sight equipment. I had them give me the same point a couple of times and varied by as much as 3/4". Gps for carpentry sucks.

[JeffB]

I have a generic version of the flourescent green one William McCormick linked to. Forgot the brand name but got it at Wal-Mart. Self locking is nice. Just have to keep an eye on the guys in the shop who are too lazy to make a mark, just leave the tape on it and start cutting with the torch. Of course, 1/4 inch off won't hurt much with what we do.

[scubaholic]

when i worked in the fab shop they supplied starret 16 ft tape measures and thats all u were to use no matter what

[HGHS-Corp]

Please... use your logic sense...a tape that is 8meters(315") will maybe expand 3-6mm(0.12-0.24") on the total 8meters, while going from 5C(41F) to 30C(86F).

And i don't know what the maths says, but it is logic sense.
Otherwise buy a measuring tape that is ANSI certified.

[William McCormick Jr]

Originally Posted by HGHS-Corp

Please... use your logic sense...a tape that is 8meters(315") will maybe expand 3-6mm(0.12-0.24") on the total 8meters, while going from 5C(41F) to 30C(86F).

And i don't know what the maths says, but it is logic sense.
Otherwise buy a measuring tape that is ANSI certified.

General Motors claims that their cars grow 1/8" on a hot day compared to a cold day.

Perhaps the other fellow meant that the change is over 10% of an inch. Or 10% of an increment.

Sincerely,


William McCormick

[steve45]

OK, the thermal expansion coefficient for steel is: 0.00000645in/in/deg °F.

A 100' steel tape would be 1200 inches, and it would expand/contract 0.00774 inches per °F.

A 50 °F temperature change would cause a change of 0.387 inch.

[Knotbored]

A hot steel tape will measure a cold aluminum part wrong-but a hot steel tape will measure a hot steel part right, and a cold steel tape will measure a cold steel part right.
The problem is only when the steel tape and the steel part are significantly different temperatures.
If you take a steel tape from your warm pocket and measure a critical part in Adak Alaska at Christmas you will get it wrong!

[Brianstick]

I've got top of the line Starrett tapes and I have tapes that I got from the Dollar Store. For what I do around here they both work fine. We're talking about tape measures, not micrometers.

[wagin]

Originally Posted by Brianstick

I've got top of the line Starrett tapes and I have tapes that I got from the Dollar Store. For what I do around here they both work fine. We're talking about tape measures, not micrometers.

OK, take your dollar tape and your Starrett tape, hook both to a common line, pull out 5ft, then 10ft, etc and see if the readings differ. I have seen cheap tape show .125 variations in less than 3 ft. Of course this false reading increases with distance. I have been required to produce sheet jobs with +/- .062 across several feet and I have pre-fabed jobs with 10" I-beams spanning 20+ ft. Even on large scale jobs, a .250 to .50 inch makes a great difference.

[Brianstick]

I tried tour your today up to 11ft. and guess what? There was no difference. I do see your point though. Maybe for someone like you it would be worth your while to stick with brand names. Personally I like the Stanley tapes, but when I go to the Dollar Store and see a basket of 16ft. tapes for a $1.00 each, I've got to grab a couple.