Tape Measure Accuracy

      Even before they get dropped on the shop floor, tape measures are unreliable. Calibrating your machinery instead might work better than relying on any tape. May 13, 2008

Question
I have been having big problems with tape measures. I have been using Craftsman, but have been having a lot of inconsistencies lately. If I pull 36" on 2 tapes and line them up together, I get a 1/16 difference. I have tried a few others like Stanley and get inconsistent measurements there also. It's been really causing a headache around the shop, especially when two men work on one project and the tapes don't match up. Things are getting out of square or cut short. What's the best out there?

Forum Responses
(Cabinetmaking Forum)
From contributor E:
I bring a 12" steel rule with me and go through several tapes with the push/pull test before I find a good one. Usually Stanley Powerlock.



From contributor S:
Have you looked at the tip of the tape measure to see if it is bent? I take them all and put the tip on the side of my table saw and tap it with a hammer. I know this never happens in a cabinet shop, but maybe someone dropped it on the floor. You should check any of the squares you use in your shop as well, because you might be surprised to find out they are not square either.


From contributor C:
Several guys in our shop swear by Starrett tape measures. 12 ft and 16 ft all metal cases. The rest of the guys use FastCap Green and White ones. The white one reads all the way across and the yellow reads both sides separately. Very durable. I think the FastCap 16 ft is a little bulky.


From contributor M:
The tapes that work the best for me are the Tajima G series. They have a black rubber case that protects the hook end on the tape from being bent when dropped. That, more than anything else, has led to inaccurate readings on my tapes. The only downside is that you have to grab the hook end and extend it to get it started rather than just hooking the tape itself. With as often as I drop tapes, it's a small price to pay. They come in English/metric combinations also, which I like to use. I haven't encountered a problem with any of their tapes not reading consistently from one to the other. That's all that's used in my shop.


From contributor D:
Fat Max Extreme 25'. Anything less is for decorators and seamstresses. Stop whining about heavy tapes; be a man.


From contributor B:
What are you using the tapes for? Measure, mark a line and cut? Doesn't work! Put measuring devices on your equipment, calibrate them, and use the pocket tape only for approximant evaluations. At that point you have a chance of repeatability.


From contributor V:
I like contributor B's idea.


From contributor J:
I, too, am with contributor B. I would add that I force myself to have only one tape in the shop at a time and do my level best to use just that one tape on all hand measurements in a given project. That way, if the tape is slightly off, all the parts are slightly off together.


From contributor P:
Contributor B has it right. All of our machinery is calibrated from a single steel rule. Tapes are resigned to checking general lengths and aren't counted on for layout, but we do have a master tape that we use if we need it. The master tape is the only one used on a job and it's babied to keep it from getting banged up. Most manufacturers offer sets of tapes that come from the factory calibrated to one another.


From contributor K:
I went through this 20 years ago. Called several of the tape manufacturers, Starrett, Stanley, etc. and got the same answer from all. Tape boxes are only accurate to + or - 1/16" and will vary from + to - over the length of the tape. I went to all digital from Accurate Technologies for all the critical machines and love it. They are accurate to + or -.002" every day of the year!


From contributor A:
I was watching a TV show the other day called "How It's Made" and one of the things they showed is making tape measures. At the end of the manufacturing process, they had a human checking the tapes' accuracy. Those that were within tolerance went into the good box and those that were out of tolerance went into the bad box. They never said what the tolerance was or where the "bad box" of tapes went. I assume the out of tolerance ones went to the cheap retailers and the others went to the well-known companies. Point is, with the speed that these things were printed, it's no wonder none of them match. I always have a folding rule with me for repeatable measurements, and they seem to be closer from one to the other than tape measures. Just wish the marks were finer. But no matter what kind of measuring stick you use, always use the same one for one job.


From contributor W:
The best way to check the accuracy of your tape measures is to make a master jig to check them. Take a 3" x 3" x 1" piece of Plastic UHWM or something that is stable and will not contract or expand, and run a 1" dado exactly down the middle of it about 1/2" deep. Now you have the perfect jig to test the tape measure with. You can pull the tape across the jig on the high point to see if it is 1" and then place the metal tab in the dado and push to see if it measures the 1" dado. The push/pull should be the same.


From contributor K:
The problem with tape measures, according to the info I got from Starrett and Stanley, is that it may read perfect at say 24", then at 48" be short of perfect up to 1/16". Then at 72" or 96" be 1/16" over perfect. The difference can drift to a + or - variation at any point over the length of the tape. This is what pushed me to digital rulers on four of my machines.


From contributor M:
Just out of curiosity, and to test my tape measures, I took an 8' strip of scrap plywood I had left over from a job and started cutting it to length in 1 foot increments using the digital crosscut fence on my saw and measuring after each cut to see how it compared with my tape measure. Starting at 95" and working down, I couldn't see any variation in my tape measure readings vs. the crosscut readings. I'm going to stick with my Tajima tape measures, although if I ever got a chance I would take a look at the Stabila tapes also.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
I used to be responsible for the Quality Assurance system of a 50 plus person shop. I gave up on letting people furnish their own tapes. We started furnishing Stanley 12' and 16' tapes to everyone. I had one master tape which was used for calibrating/checking new tapes. I would buy 10 at a time from McMaster. They were checked at 2', 4', 6' and 8'. If any were found to be off more than 1/32" at any point, they were used only in the rough mill. With adjustment of the hook end, very few did not meet the cut.



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