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stanley tape measure accuracy

#260486 by Meeri » Fri Jun 14, 2019 3:23 am

Yesterday I needed to cut some 1 1/2 x 25 x 3/4 stiles. I pulled out my Stanley 16 ft tape measure and measured 25 inches and marked the wood from one end. Since I was going to be making a lot of these I wanted to be very sure that they were cut accurately so I checked it against two metal rulers and found that although both metal rulers (one an old carpenter's square and the other a new machinist's square) and found that although both agreed that 25 inches was 25 inches, neither agreed with the Stanley tape measure. The steel rules were consistently about 1/6 more than the tape measure. I then picked up another steel ruler, this one only 18 inches long and measured 18 inches plus 7 inches. This resulted in the same mark as the other metal rules.

Am I wrong in expect less than 1/16 accuracy over 25 inches of the Stanley tape measure? FWIW, I checked it with a 25 ft Stanley tape measure and it measured the same as the 16 ft tape measure.

I ended up using the mark from the metal rule and then cut all 16 of these stiles to the same length using a stop-block. It was more important that they all be the same than that they be exactly 25 inches. Yet, 1/16 in 25 inches means a lot when you are trying to join multiple pieces together squarely.

Any thoughts by other woodworkers? Is it just Stanley or was I expecting too much from a tape measure?

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Re: stanley tape measure accuracy

#260487 by GoNavy » Fri Jun 14, 2019 5:10 am

Almost all tape measures utilize the hook end to compensate for measurements inside/outside...meaning the end moves in when against a wall etc...and moves out when hooked over a board end. They are notorious for getting stuck and not moving, bent, or just plain old and more loose then they should be....usually I do the burn an inch method if accuracy is really needed, in other words I start at the one inch mark and just add the inch to the other end. The only problem with that is getting forgetful and forgetting to add that inch and cutting the stock too short...lol..it happens

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Re: stanley tape measure accuracy

#260488 by dusty » Fri Jun 14, 2019 5:22 am

Burn the inch as suggested by GoNavy and recheck your Stanleys. I'm betting on Stanley being as accurate as the steel rules.

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Re: stanley tape measure accuracy

#260489 by BuckeyeDennis » Fri Jun 14, 2019 7:01 am

I have a friend who works at the local Woodcraft store, and he told me that they once checked the accuracy of all the tape measures on their shelves. They were ALL off by at least 1/16”, although I don’t recall over what length.

So while tape measures are fine for rough carpentry, or for relative measurements if using the same tape measure, they aren’t suitable for high-precision absolute measurements.

I have a couple of American-made 24” heavy steel machinist’s rules (Starrett and Lufkin). These would cost a couple hundred dollars each new, and they agree with one another to within the resolution of my eyesight. I always check my other rulers against them. My Stanley tape measure is noticeably off, and it’s not just offset from the sliding hook. But my DeWalt is pretty accurate — at least over the first two feet.

Sadly, even Starrett’s (inexpensive made-in-China) steel adhesive tape measures have poor accuracy. I didn’t trust the reviews reporting this, so I bought a couple to test myself. Sure enough, the accuracy is inconsistent along the length of the tape. It’s as if feed rollers were slipping as the tape was fed through the printing machine.

I recently had need for a highly accurate 4’ / 1200 mm rigid ruler. I tried hard to find a good one for under $50, but everything I checked in that price range had accuracy problems. This was generally due to the sides and ends being sheared (and therefore not square and parallel) instead of machined or ground. I wound up paying about a hundred bucks for a Woodpeckers ruler. It’s really nice, although it still disagrees with my machinists rules by maybe 0.005”. But that’s good enough for my purposes, and I have no way to tell which is more accurate.

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Re: stanley tape measure accuracy

#260490 by dusty » Fri Jun 14, 2019 7:54 am

What level of accuracy is reasonable to expect of a ruler or tape measure that is marked in increments of 1/16" or even 1/32".

1/16" = .0625"

1/32" = .03125"

If expecting measurement accuracy at the .005" level I hope you are not marking the cut point with a lead pencil.

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"Making Sawdust Safely"
Dusty
Sent from my Dell XPS using Firefox.

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Re: stanley tape measure accuracy

#260491 by RFGuy » Fri Jun 14, 2019 8:09 am

Some excellent responses on this thread and I agree with all of them. Just to expand a little on BuckeyeDennis comments, it has been my impression that there are layout tools (like rulers) that are meant for rough carpentry and those that are meant for finish carpentry or more precision work, so you have to know when to reach for one versus the other. In my mind, a tape measure has always been for rough carpentry work (think house framing) where often being off by a 1/16" or even an 1/8" is "okay". I have a nice metal housing Lufkin tape measure (25') that I have had and used for 2 decades now. I use it often for rough cuts, but when I want a precise cut I would reach for a machinist ruler, if I had one, or use my folding carpenter ruler (pic below). I have had my carpenter ruler for decades and I have received very consistent results from it, though the newer ones seem to have bad reviews online so maybe they aren't built the same now. I know about the inside versus outside measurement difference on a tape measure end tip, but in addition to this as a tape measure wears the rivets that hold the tip on tend to wear and cause this end tip to move more side-to-side further upsetting the measurement. If you have a precision fixed ruler that is always best, but for long measurements, I reach for my carpenter ruler which has served me well. Bottomline, it is great that you are checking your measurements. Sources of error can creep in from many different directions, so we have to be vigilant to ferret them out.

Also glad that BuckeyeDennis pointed out the Starrett adhesive tape measure limitations...I had wondered about that as more equipment is made in sources of cheap labor. Related to this - I finally broke down and bought a Mitutoyo caliper for my shop. I have been wanting one for almost 3 decades now and finally purchased it. I was surprised how many counterfeits (knockoffs) are out there. The attention to detail in copying an instrument like this is amazing so you have to be very careful on these purchases, or you may not get the precision that you are looking for...Just Google counterfeit Mitutoyo caliper and check out the YouTube videos on the subject before purchasing (if you are in the market for one).


klein-tools-rulers-900-6-64_1000.jpg
klein-tools-rulers-900-6-64_1000.jpg (73.91 KiB) Viewed 6659 times

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Re: stanley tape measure accuracy

#260492 by Gene Howe » Fri Jun 14, 2019 8:51 am

As Ronnie said, " Trust but, verify." My tapes stay in the drawer, for the most part. 123 blocks, keyway stock, pinch rods and story sticks are my go to tools for measurement and, tool set ups. When a length is needed that exceeds the capacity of those tools, a metal folding rule used but, with the understanding that it'll still just be close. The numbers and graduation marks are just for reference, anyway.

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Re: stanley tape measure accuracy

#260493 by Ed in Tampa » Fri Jun 14, 2019 9:15 am

I do not believe tape measures were ever intended for precision work. They are carpenters tools and as such are perfect, a 1/16 of an inch is nothing in the construction of a house.

Also in almost every drop test, testers find that the hook is usually the first thing damaged on the tape measures. Again they were never intended for precision work.

Use steel rules, burn an inch or story sticks if you want closer than 1/16 precision work.

Also whatever you use, use it for every measure so if there is an error it will be the same always. You sure don't want to use one that measures short and one that measures long on the same job.
Last edited by Ed in Tampa on Fri Jun 14, 2019 9:20 am, edited 1 time in total.

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Re: stanley tape measure accuracy

#260494 by robinson46176 » Fri Jun 14, 2019 9:19 am

I did the "burn an inch" thing for many years (on critical stuff) but now I try not to. I now try to burn 10"...
10" keeps it simple but is far enough away from zero so that you are less likely to forget the inch. If you are cutting a piece 25" long and forget the inch you might not notice but if you are 10" short you will probably notice a 10" inch shortage... :)
I forget where I read about that.
I carry a smallish 10' steel tape at all times including weddings and funerals etc. :D
99.9% of the time a steel tape measured from the end hook is "close enough" for what I measure. I do have a couple of good "steel scales" for close work. Some stuff I measure requires even less accuracy than that (Think farming stuff). I keep a couple of sight levels, a transit, a surveyors "chain" tape and a large measuring wheel but if I'm fencing a temporary horse lot I might lay it out by saying "OK, from here (kicking my heel into the dirt) to over by that rock to just past that stump and then to that big weed over there"... :D :D
In the woodshop about the most relaxed I get measuring is that I have a batch of wooden yardsticks and keep some stationed at various spots around the shop. They are there mostly for things like grabbing a scrap piece and seeing if it is the right size to cut a needed part from or "will that scroll saw squeeze in this gap?"
I do have one other loose measuring device I use some. I have an 8' furring strip that I marked off in feet and I grab it to check space if I decide I want to rearrange any big stuff. It just helps me think a bit better.
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In woodworking I always try to not measure when possible. I subscribe to the old adage "Never measure when you can superimpose"... If I need a batch of a piece I was always taught to make one and mark it as the pattern "pat" and use it to mark the rest. If I'm doing close work I usually grab a Sloyd Knife to mark with instead of a pen or pencil.
https://bluesprucetoolworks.com/blogs/new-tools/who-was-sloyd-and-what-was-so-special-about-his-knife
None of these look anything like what I grew up calling a Sloyd knife but are very much like some of the knives used by shoemakers and leather crafters. I still have all of my many knives from that part of my life and do use them in the woodshop on ocassion.


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farmer
Francis Robinson
I did not equip with Shopsmiths in spite of the setups but because of them.
1 1988 - Mark V 510 (bought new), 4 Poly vee 1 1/8th HP Mark V's, Mark VII, 1 Mark V Mini, 1 Frankensmith, 1 10-ER, 1 Mark V Push-me-Pull-me Drillpress, SS bandsaw, belt sander, jointer, jigsaw, shaper attach, mortising attach, TS-3650 Rigid tablesaw, RAS, 6" long bed jointer, Foley/Belsaw Planer/molder/ripsaw, 1" sander, oscillating spindle/belt sander, Scroll saw, Woodmizer sawmill

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Re: stanley tape measure accuracy

#260495 by thunderbirdbat » Fri Jun 14, 2019 9:43 am

While some tape measures are checked for accuracy, none of the ones I have seen were. The tape measure is marked with roman numerals when it is checked for accuracy. Here is a decent descriptions of the makings found on a tape measure. https://www.thetapestore.co.uk/knowledgebase/How/Tape_Measure_Markings_%E2%80%93_What_Do_They_Mean_.html

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Brenda

1998 510 upgraded to a 520, upgraded to power pro with double tilt and lift assist.
1998 bandsaw
2016 beltsander
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