Meauring Stuff Is Impossible


A recent thread on using tape measures in the shop got me to thinking about this.
I went on Starrett's website and found that the most that they will write up a Certificate for on a tape is +/- 1/32". They also say on that website that whatever tool you use to measure with should be capable of measuring to 1/10 of what your tolerance is. So, if their best tape is only capable of +/- 1/32", then my tolerances can't be any tighter than 5/16", which seems a tad generous to me for cabinet work.
I have some Starrett and Rabone-Chesterman metal rules that will measure to 1/64", which would allow me to have tolerances of a little heavier than 1/8". I guess I could use these rules for framing houses - but they still aren't accurate enough for building cabinets.
I have a Starrett dial caliper that will measure to 1/1000" - now that will let me have tolerances of about 1/100", which is heading in the right direction but when I think about it, a piece of newsprint is about 4/1000", or 1/250" and I know that my joints are tight enough, when they are cut properly, that I can't fit a piece of newspaper into them.
And yet, that can't be possible because the best measuring instrument that I have in my shop will only allow me to have tolerances of 1/100".
It makes you wonder why framing carpenters and masons even bother to own measuring devices at all and, it has been my suspicion for some time that many of them don't.
It is gratifying to me that I am capable of doing the impossible but it makes me a bit squeamish, if you follow me. A man needs to know where he stands in this world and how can you do that if you can't measure anything proper like?
When I had my first philosophy course in college we studied this old boy named Zeno the Eleatic and his paradoxes. Now, Zeno said that you can never get from one place to another because, first you have to cover half the distance from A to B, then you have to cover half of the remaining distance and then half of that remaining distance, and so on for ever and ever. So, there's no sense in trying to measure anything because it just ain't gonna work out.
Zeno may have been the first framing carpenter, although I am not entirely sure about that - nor anything else, it seems.
Regards, Tom.
Thos. J. Watson - Cabinetmaker http://home.comcast.net/~tjwatson1 / tjwatson1ATcomcastDOTnet
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wrote:

I wonder what's their justification for that statement. Seems to me that a measuring capability smaller than the tolerance is simply unnecessary, unused precision.
Tom Veatch Wichita, KS USA
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Tom Veatch wrote:

That is a typical rule of thumb for test equipment in a factory environment, particularly for electronic equipment. Not sure that such a rule of thumb would be applicable to cabinet making.
--
If you're going to be dumb, you better be tough

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adjustments of equipment as the process goes forward. With a go/no go gauge, you don't know if anything needs adjustment. You just know it's in tolerance. When it gets out of tol. the process must stop, make adjustments, and then rework that item(s) . Many engineers forget about tol. stack up, or worse, have no idea what is is.
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Zeno might be an optimist.
Anyways, any measuring tool is a best guess in my mind. I was told by a friend to make sure I always use the same measuring tape, rule, etc for a job. In that the differences between tapes from the same manufacturer is sufficient to cause your measurements to be off.
Within a tape there could be differences as well, right? Isn't that a reason for test cuts?
MJM
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Yes!
It has to do with how steel measuring tapes are made and the marks printed on the steel. Plus the steel measuring tapes are affected by temperature.
The error noted by Starrett of +/- 1/32 is the error of their marks (indications on the tape) being "true", nothing to do with user's error to transfer marks to working stock. Error is Starrett's not your craftsmanship.
Sorry, but this is all basic Prof. Deming process control stuff that the Japanese beat up the USA over back in the 1970s and 80's; AKA Quality Control. And are now being use to great success by the Chinese.
Again, it has to do with how steel tape measures are made, not your craftsmanship. White dot / Red Dot your Yo-Yo tapes. Use only one per project. Just turn your dotted tape into a modified story stick, and stop thinking that an inch is an inch by any other stick.
Just IMHO.
Phil
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Phil Again wrote:

While this is true, I do try to get my tapes close to "true"... I test them against an accurate steel rule when in the store, and only buy ones that match the rule. This ensures that the first foot or so is accurate.
So far I've had pretty decent results, but I still generally stay with a single tape for a given project.
Chris
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Chris Friesen wrote:

FWIW, Fastcap has a couple of tapes http://www.woodcraft.com/family.aspx?FamilyIDX29 that are designed to be used as story sticks, with inch marks on one edge and the other edge blank write-on. One is the one that says "Story Pole" and the other is the "Flatback".
Won't swear to their accuracy (really, if you want accurate bite the bullet and get a Starrett) but the story pole feature can be damned handy, especially seeing as you can carry 16 feet of it in your pocket.
--
--
--John
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Phil Again wrote:

My tape IS a story stick!
It's the PS-SP: <http://www.fastcap.com/products.aspx?id46
It's got a pencil sharpener and note pad, too.
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Tom Watson wrote,on my timestamp of 11/08/2008 7:54 AM:

If they are anything like me, they just grab a story stick and mark away, then read off the marks for that project and the next one along same. Much more precise than any tape measure.

join the club...
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I'm just barely a journeyman wood smasher, but measurements using a tape are just to get the board to the rough size. I never trust the little metal clip on the end, but use the painted marks after that. I CHECK the overall measurement using the metal clip, to make sure I have the right number of inches. I do use metal rules, 6 or 12 inch, for most things without problems, but even with a steel rule in 100th of an inch markings, I don't think you get the needed repeatability. With my limited experience, I try and plan my cuts so that all like boards get cut exactly the same. For example, if I need some boards 5/8" thick, I plane them all at the same time, checking with a dial caliper. Once the first board is correct, I can do a last pass on the rest, and they will be close enough to each other. Then, the actual size can be 5/8" +/- whatever, and they will all be the same. I have not learned how to fit boards together well enough to just saw and glue. I have to fine tune each joint as I go to get a fit that is visually "invisible". Takes a while longer, but the embarrassment of having friends and family see a poor joint on furniture lasts much longer.
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rich wrote:

Realistically, most people probably wouldn't notice unless you pointed it out to them. As a hobbiest, really high quality joinery is for the benefit of the maker, not the viewer.
Chris
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That's reason enough.
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wrote:

Are you still here?
If you are you and you are still here - good on you brother and did you ever get a solid piece of land to live on?
Did you ever even get to unpack all your gear?
Regards, Tom.
Thos. J. Watson - Cabinetmaker http://home.comcast.net/~tjwatson1 / tjwatson1ATcomcastDOTnet
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Tom Watson wrote,on my timestamp of 12/08/2008 11:52 AM:

hope so! :)

Yup. after 4 years of sheer pure hell with a dishonest builder. All sorted out now, we won all the battles. Lost a lot of moolah in the process and it's taken us a while to get back to normal. Plus the usual family troubles from very old relatives. But it's all under control now, almost back to normal.

Er........ (next question?) LOL!
Actually, yes. I'm in the process of finalizing the gar^H^H^Hworkshop with all the stuff I had before - and a lot more. Another 3 or 4 months and it should all be sorted out and working like a charm. Mind you: I'm still a galoot at heart, so "working" is probably not the best word choice... ;) The kids are now old enough to give me a hand as well so that makes things a lot easier.

Good to hear from you, Tom. Anyone else from the old gang still around? I've followed the porch all these years although no time to participate. But here I totally lost contact until a coupla months ago.
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If your tongue is planted firmly in your cheek for too long a time - can it go into spasms?
Regards, Tom.
Thos. J. Watson - Cabinetmaker http://home.comcast.net/~tjwatson1 / tjwatson1ATcomcastDOTnet
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Tom Watson wrote:

Go ahead, tell us.
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A charley horse is within the realm of plausible! Tom
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Waddabout marking out accuracy?
oblique blunt crayon works fine for me,
--Zeno the Elastic
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