[OP]
Friend of The Creek
Worst measuring tools?
I'm working on a presentation on measuring and discussing things like precision, accuracy, repeatability, resolution and so on.
I'm also going to start by talking about the fact that not all measuring tools are accurate or equally accurate.
I would like to find some really inaccurate tools for the demonstration.
If anyone had any they would like to sell I'd be happy to buy them or trade new tools for them.
Thank you,
Tom Walz
I'm a Creeker, yes I m.
I fries my bacon in a wooden pan.
Member
Like my Ronco Rolling Ruler?Originally Posted by Tom Walz
Member
Can't go wrong with any of these gems: http://www.harborfreight.com/hand-to...crometers.html
Member
Like this Starrett ruler? Some folks were incredulous that a Starrett product could be less than accurate. So was I until this ruler arrived. But return shipping is more than it is worth and it still makes a good straight edge. The middle ruler is from Rockler. Nicely engraved markings and dead on accurate based on the Incra fence system. Bottom ruler is an old, dropped, beat up Johnson that still works sufficiently well for most tasks. Fastcap and Stanley tapes are sufficiently close for carpentry.
Member
This is kind of funny, but actually serious. I don't know your audience, but:
Stepping off with your feet. Have three people measure the room across and back. Bet you get 6 different answers. Be sure to pick a big guy and small woman. Then pick another person who has the same size feet as one of the others.
Using your fingers as calipers. "Its about this big" I bet most people couldn't pick the the block sitting on one table from a few similar sized examples that matches a reference block sitting on another table across the room
Weighing using your hand. Be sure to move it up and down--that improves the accuracy
You can keep your tools thought--I want to keep my hands and feet.
Last edited by Matt Meiser; 10-04-2011 at 1:56 PM.
Member
The problem to me is you have to define desired accuracy and then pick a measuring tool to do the job. The cheapest HF tape measure should be plenty accurate enough to frame a house. I doubt you would see an engineer at NASA measuring a part in the metal lathe with it though.
The point being that of course all tools are not equally accurate, but that doesn't mean that a less accurate tool is inaccurate for it's intended purpose.
Then of course you could get into where a lot of the inaccuracy comes from.....the person doing the measuring!
anyway, just my random thoughts....good luck,
JeffD
Member
May be the Starret ruler is calibrated as an outdoor ruler when it is very, very cold.
Jeff
Thank goodness for SMC and wood dough.
Member
I think gov't. spec. accuracy for a tape measure is 3/16" out per 6'. I haven't really seen one that much out,but thought it worth mentioning. I bought a 20' long tape measure from a bin in the grocery store for less than $4.00. It is right on,just fine.
Member
George Wilsons post http://www.sawmillcreek.org/showthre...-rules-we-made was interesting about accuracy of folding rules.
Are you asking us "If you were sitting through a presentation about precision and accuracy would you use a ruler or a watch to see how long it is until break time?"
I make dirt out of woodworking tools.
Member
Take any good ruler, or any good measuring tape. For all of them applies the same. There is a measuring done when placing it, when deciding on the mark to tick off at and when doing the tick off with a pen or knife, and when aligning a tool to the mark. Every time you measure, this contributes to give a different result. Measuring is inaccurate.
The alternative is not measuring better, rather it is not to measure.
If you do 5 shelves in a book case with the measuring method, you get 5 different lengths. Some of them might be close. If you instead set up the table saw once, and make 5 cuts without remeasuring, the difference in length will be very little. Repetition beats measuring.
Measuring compared to repetition is about as good as comparing a one meter ruler used to measure a meter, with a 25 centimeter ruler used for doing the same measuring.
--- Mats ---
Contributor
In defense of the L.S. Starrett Co., the aluminum yardstick with Starrett's name on it is just an aluminum yardstick. Starrett has a line of contractor/homeowner grade tools. I believe they purchased another company and just put their name on them. These tools have nothing to do with their line of precision measuring tools costing many times what that yardstick cost. A 1 1/4" x 36" rigid steel rule with 4r easy read graduations(1/8" 1/16" 1/32" 1/64") cost $156.00. Aluminum yardstick $15.00.
Contributor
Measure it with a micrometer, mark it with a piece of chalk, and then cut it with an axe. Precision work, measured to the thousandth!
Member
An example that comes to mind is the magnifying bubble cursor which comes with some table saw and miter saw stops. You know, the kind that reads totally different depending on the angle you view it?
My shop fox fence on my grizzly saw came with one, and I got it out of my shop as soon as possible.
http://www.sawmillcreek.org/showthre...ing-the-curser.
Another example is too close of increments. I've never once used the 1/64 side on my starret combo square as it looks like solid grey to my eyes. I can interpolate pretty close to 1/64 with the 1/16 side though.
Member
You could demonstrate how "pencil creep" happens when you use each successive piece you cut as a pattern for the next. Or demonstrate the "rule of thumb" that has its origins in English common law that limits the size of the stick you can use to beat wife to one that is no thicker than your thumb.
As for tools, the most inaccurate tool I came across is a laser on an older 12" Bosch sliding miter saw. The line moved close to 1/16" as I lowered the blade to make my cut. The new "Glide" version of the saw solved the problem by eliminating the laser!
Member
How is Starrett pimping their good name in order to fool consumers into thinking they are buying something they aren't a defense?
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