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+-- Thread: stanley tape measure accuracy (/showthread.php?tid=7332958)
RE: stanley tape measure accuracy - MstrCarpenter - 09-06-2017
I've been using tape measures for quite a while. I have never started my day by comparing my tape to others. When I have compared tapes, it was usually a result of not getting the length I asked for. The cause was usually a bent tip, and less frequently the rivet holes have elongated to more than the thickness of the metal tip, so I do check that my tape shows identical inside and outside measurements.
I don't measure and cut to the closest 64th, but I do consistently measure and cut to about .010" tolerance with a Stanley tape and 15" Hitachi chop saw. On my jobs we measure to the closest 16th and call out strong or shy and write + or - when appropriate. (i.e. 9/16"+ is not the same as 5/8"- )
RE: stanley tape measure accuracy - handi - 09-06-2017
Before buying a tape at the store, I extend it some inches, then fold it back on itself, aligning the marks to see if they line up over several inches. You'd be surprised how often they do not, even between examples of the same unit.
RE: stanley tape measure accuracy - Handplanesandmore - 09-06-2017
(09-06-2017, 07:49 PM)handi Wrote: Before buying a tape at the store, I extend it some inches, then fold it back on itself, aligning the marks to see if they line up over several inches. You'd be surprised how often they do not, even between examples of the same unit.
That is interesting! Never tried that. If I need another tape....
Simon
RE: stanley tape measure accuracy - Jim Waldron - 09-07-2017
(09-06-2017, 04:59 PM)Handplanesandmore Wrote: Yes, I do mean accuracy, not precision. Being precise but not accurate is useless, whether in engineering or in woodworking.
[snip]
Indulge me in one additional thought:
When I'm making a drawer, with plans that call for, say, 21 inch sides, I'm happy if my 21 inches are somewhere in the ball park of 21 inches. Accuracy doesn't really matter all that much as long as it's not too long to fit in the casework. What I do care about is that both sides are precisely the same length so that my drawer comes out square. I work hard at that precision.
That precision is far more useful than accuracy so that the drawer functions properly. If it comes out at 20 inches rather than 21, who cares? Who will know? Or to plagierise a quotation, "What difference does it make?" But if the drawer is imprecise and out of square, everyone who struggles to open or close the drawer will know.
There are circumstances, in both engineering and woodworking, and even in commercial construction, where accuracy matters, sometimes a lot. But the more it matters, the less reliable it is to use a tape measure with all it's built in inaccuracies. That's even when using only one tape.
RE: stanley tape measure accuracy - hbmcc - 09-07-2017
A few authors have stepped into the accuracy vs precise debate regarding tape measures, and measurement generally. Tolpin comes to mind with his sectors and thumbs and fingers, together with proportions.
In cabinet making you don't need a measuring stick. You need a square and marking gauge. Maybe, a story stick. Until the plans call for a 30 foot arc. In that case you can play the proverbial thumb twisting and hunt for a bendy stick. When I prepare stock, I go from gross to final to finished that started with a cartoon I churned out in CAD having precision to 4 decimals. If I need 21 feet of wood and have only 20, the plan is adjusted; or, I go shopping, only if the extra foot is critical. And, it is critical only if I am filling a hole that requires an exact fit.
The only people who need Starrett tools are machinists. The rest of us can limp along with computers, lasers, pencils and thumbs.
PS. Did you know warehouses, even a quarter mile long, have a maximum floor variance of 1/8th inch in elevation? That's good until the soft foundation settles, or we have an earthquake.
RE: stanley tape measure accuracy - Handplanesandmore - 09-07-2017
"And, it is critical only if I am filling a hole that requires an exact fit."
and only if you are using manufactured materials like mdf.
With hardwood, the perfect fit is not the gap-free, airtight fit kind, but one that allows for wood movement, which can mean a gap of 1/64" to 1/4", depending on so many many things.
The talk of accuracy and precision, therefore, is all relative for woodworkers and engineers alike, depending on the materials in question. All metals, concrete and wood expand and contract.
As a woodworker, all I am interested is durability and final appearance. As long as I can get there, I don't care if my device is off by 0.25mm or 1mm.
Simon
RE: stanley tape measure accuracy - toolmiser - 09-07-2017
Since this is getting a little heated, how do you know when any of them are correct? Just because "some" agree, does that make them right? As someone mentioned if you stick to a single measuring device you should be somewhat ok. My problem is that they tend to disappear like pencils and then what do you do.
RE: stanley tape measure accuracy - Handplanesandmore - 09-08-2017
(09-07-2017, 08:50 AM)Jim Waldron Wrote: Indulge me in one additional thought:
That precision is far more useful than accuracy so that the drawer functions properly. If it comes out at 20 inches rather than 21, who cares? Who will know? Or to plagierise a quotation, "What difference does it make?" But if the drawer is imprecise and out of square, everyone who struggles to open or close the drawer will know.
There are circumstances, in both engineering and woodworking, and even in commercial construction, where accuracy matters, sometimes a lot. But the more it matters, the less reliable it is to use a tape measure with all it's built in inaccuracies. That's even when using only one tape.
Jim, Using your drawer construction as an example, this is how I see it.
For the drawer to function properly, you must first decide what its final dimension should be (by measurement or by butting the stock against the opening). As long as the dimension arrived at is the same or smaller than the opening then it will work physically. Say, the width for the drawer front should be 21".
Accuracy: You cut the front to spec. accurately at 21", using the measuring device as the guide (the same tape, stick, whatever that was used to arrive at the 21" figure in the first place). The drawer now goes in as it is designed to.
Precision: You cut the front precisely to an inaccurate width (21" + 1/64"). The drawer can't go in. So, you re-cut the front precisely, this time, also to another inaccurate width (21" - 1/64"). The reveal is now 1/64" larger than what you sought to attain. Is it fatal? It depends on your goal. For a shop build, no one would care, but if you were supposed to deliver an air-tight (piston-fit) construction to your client, you could be in trouble. Or every drawer has an even reveal except this one, the odd man out that everyone can see, including yourself.
When you say 20" or 21" and who cares, it means you are the boss and you can change the design or dimensions on the fly (most of us often do that either to accommodate the stock or to cover a mistake we make). That however is different from the question of accuracy vs precision.
RE: stanley tape measure accuracy - bandit571 - 09-08-2017
I use the same tape through out a project, period.
It is more about IF I trust a tape, than checking the dang thing every morning.
Useless waste of time, actually. 
IF I trust the tape I am using, then it will continue to BE used. Seen way too many older tapes, with their ends all beat to hell..
..no way would I trust one of those, simply because of the little clip on the end will be...POS. 
BTW: have you compared a Stanley Powerlock tape to the same sized Luftkin? Or, some other brand name maker?
RE: stanley tape measure accuracy - Admiral - 09-08-2017
(09-08-2017, 01:15 PM)bandit571 Wrote: BTW: have you compared a Stanley Powerlock tape to the same sized Luftkin? Or, some other brand name maker?
On the occasion when I have the need for a new tape measure, I take an accurate scale with me, generally my 24" starrett scale, and compare the tapes on the rack. My experience has been that more than half are off about 1/32" to a sixteenth over a two foot length, which is pretty much ok for construction work, and if you are patient and continue to check you'll find one dead on; they will wear with use, so as they get older some of my tape rules get relegated to "rough' work, and I generally lose some, so I average one new tape every 3 or 4 years. I then use the newest one for furniture projects, but again for "close enough" work, and generally fit pieces with a miter plane, Lion trimmer or chisel. Works for me.