Tape-Measure Accuracy
Like everything else in life, tape measures are imperfect. But here are a couple of suggestions for improving accuracy. October 11, 2007
Question
We keep running into the same problem, accuracy or precision of measuring tapes used in the shop. We need a reasonable level of accuracy. Most measure tapes have lousy agreement between manufacturers and even between tapes from the same manufacturer. We're looking for a tolerance to within 1/64th. 1/32nd is causing problems. Am I asking for too much here? Who manufactures decently accurate measuring tools? Please help!
Forum Responses
(Architectural Woodworking Forum)
From contributor C:
This is a problem all the way around. We all use .7 or .9 mm pencils in the shop to at least keep a fine line to work to. A big key is getting each person to get to know their tape measure. Each machine has to be calibrated accurately so that the tape on the machine is exactly what it cuts. Being aware of the tolerance you're generating is the first step in tightening it up. You're on the right track. I think the White Fastcap tapes are the most liked around the shop and very reasonably priced. I think the best tape is from Starrett, not easy to find, but all metal. They're all good till they are dropped a few times.
From contributor J:
Regardless of which manufacturer you use, you need to have accurate tapes, and people who know how to use them. First rule is not to drop them or let the tape slam back into the housing when retracting. Of course it sounds like common sense but we all slip up at some time. Second rule is, when you have broken the first rule, you must recalibrate your tape. By simply bending slightly the hook at the end of the tape you can get your tape's accuracy back. With the exception that after bending very thin stock, i.e. laminates, may not read accurately. But they are usually oversized anyway. Lastly, even though I try to keep my tape right on the money, I still try to measure off the 1" mark whenever I can. Just becomes force of habit after awhile.
From the original questioner:
Just to keep things on track, I'm not just talking about the accuracy of the terminal end of the tape (which can be put out of adjustment if it's dropped). I'm talking about tapes that line up on the one inch mark and are off as much as 1/32 + at the 20" mark. What's up with that!
From contributor T:
Like others said, always a problem, almost never a solution. One thing I have done is pick a location in your shop that never changes (I use a tall cabinet) or make a board to hang in your shop, use a tape that you are sure is accurate as can be, hook your good tape on it and measure down whatever length you want. Mark a very thin line, I used a razor knife, at 24" or whatever. That is your new benchmark for everyone in the shop to go by. It takes 2 seconds to check and bend the tip to make it right. Whenever I drop my tape and think it may have hit the tip, I check it. Maybe not the best solution, but it works for me. I think I would pay $50.00 for a 16 ft. tape that stays accurate.
From contributor P:
They do make one but you have to unfold it. The Germans won't use anything else :-)
From contributor L:
I feel your pain. I went around with Stanley over their tape measures. We are in the cabinet/millwork/people door business and a 16 foot tape won't do; I use a 25 footer. But when I compared different sections of my tape to other tapes in the shop, I could find it up to a sixteenth off (any 5 foot section on the tape, like accurate from 0 to five feet, then off in the next couple feet, and back to accurate if you measured out to 15 feet. Stanley took it back, told me they didn't know how it could happen, their tapes are "checked by lasers." They made good by sending me two of the last ones made in the US (new ones are now made in China), but it does make me distrust my tapes.
From contributor Y:
I abandoned Stanley tape measures years ago when I found the ones made by Johnson, (1"x25' and 3/4"x16'.) Everything I disliked about the Stanley has been eliminated in the Johnson. If you've the patience to look it up, check out the specifics in my review at Amazon.com. I just did a side-by-side test of the three Johnson tapes I own (two brand new and one used), and if there was 1/128" discrepancy at any of the foot marks, it eluded me.
From contributor A:
For true accuracy every time on flat items, we had a piece of aluminum milled 12 feet long x 3 feet wide x 2' thick with self centering tapered grooves milled every 20mm across. At one end you have your datum stop and with a Mitutoyo dial indicator with +- accuracy of 0.001, $80, fitted to the groove insert push in fit. Total cost approximately $280.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor C:
I did a lot of research on tapes for our design office. You have to start with an accurate drawing before you cut something. The tape manufacturers print the tape with a roller that can slide a little bit as it prints. Thus they can say is accurate for the whole length but anywhere within the tape there might be an area where you are off quite a lot. Every tape varies and in our shop we have learned never trust the tape. If we have to match a BS we cut a test piece and do the feel test. We have also changed most bills to decimal measurements and have digital readouts on the machines. It really helps.
Comment from contributor S:
We have also encountered difficulties with tape measures. We found that by adjusting the end hook we can often address the problem. There is a tool available from Lixer Tools that can provide you with a standard to check your tape measures against so everyone on the same project can calibrate their tape measures. We really like this tool because it will check both the push and the pull measurements of the tape measure. Often people will check the pull, but neglect to verify the push measurement.
