gage block accuracy

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What's the difference between +- .001 and +- 10 minutes?
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There is no comparison. One's a linear measure and the other is an angular measure.

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.001 is the measurement 10 minutes is the time needed to find the damned caliper to check the measurement.
The difference is that if you don't find it in 10 minutes, you use the block anyway.
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:)

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tommyboy wrote:

One's the accuracy in height (a length), the other is the accuracy in levelness (an angle)
In a woodworking group, both are far bettter than you care about.
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under the heading: How do you convert to Degrees from Degrees: Minutes:Seconds on the site, http://jwocky.gsfc.nasa.gov/teacher/latlonarchive.html
There is a whole world of surface symbols and terminology for drawings and specs, generally not needed in ww, and angle is a part of it. But this is just a format. Although this site may be showing a sphere, the calculation is the same, and the format is for angle, 360 for a full rev. 359 degrees, 59`, 59`` the next lower, though can`t say about decimals or further.
As a set of parameters it may be x dim at y angle, a parallax parameter restriction, with a reference point(s), but my bet is its a screw up.
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If you run into symbols try googling "GD&T symbols". Geometric dimentioning and tolerancing. These symbols are the words of a language. Filled in with actual values they can be combined in a bewildering combination of meanings.
http://www.tec-ease.com/gdt-terms.htm
For instance how 'straight is the cutting edge of straight shaft router bit? How to test? based on say the axis of the 1/4" or 1/2" shaft (co-axial), or compared to how flat the end is, or vice versa. Or the surface finish itself. On a complex part, wheeeee!! These shorthand lines are not limited to one liners, and also indicate machining operations.
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an egg sample
http://www.tec-ease.com/gdt-tips.htm
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http://global.ihs.com/doc_detail.cfm?currency_code=USD&customer_id !254E5C4B0A&shopping_cart_id(25285B2E4B3030415A2D58250A&rid=Z56A&input_doc_number=ANSI%20Y14%2E36M&mid=W084&input_doc_number=ANSI%20Y14%2E36M&country_code=US&lang_code=ENGL&item_s_key007418&item_key_date1231&input_doc_number=ANSI%20Y14%2E36M&input_doc_title
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To my understaanding, (and I did work in a carbide manufacturing machine shop) .001 is 1/000 of an inch. The 10 minutes is a fraction of one degree of angle. I never heard of minutes being involved the thickness. Roughly 25/1000 inch = 1millimeter.
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Nope. 1 mm = 0.03937inches.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

OR 25.4 mm = 1 inch which may be the source of the confusion - thwe 25 in 25/1000" - 1 mm
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Doug Miller wrote:

Doug, we don't always agree on things, but I'm in perfect agreement with your sig line. Where do I get my feathered headdress?
--
It's turtles, all the way down

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You'll have to make your own. Just be careful where you get the feathers. It's apparently illegal to even possess the feathers of certain species of bird, even if they're molted feathers that you picked up off the ground.
BTW -- I started using that sig shortly after the Supreme Court announced its decision in Kelo vs. New London (the eminent domain ruling).
--
Regards,
Doug Miller (alphageek at milmac dot com)
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After reading through the replies I thought of a few more things to add.
Sure enough, in many disciplines linear measurements are expressed in decimal format and even though you don't mention any units, 0.001 is often referred to as 1/1000 of an inch. Or, if you are inclined to use the metric system, this would be 1/1000 of a meter - which is very commonly referred to as a "micron".
You did choose to include units on the second example. As others have stated, a "minute" is a unit of angular measurement equal to 1/60 of a degree. Ten minutes (of arc) would be 1/6 of a degree. The "+/-" indicates that the range is a total of 1/3 of a degree (which would likely be enough to screw up all but pointy sticks and pukey ducks). Angles are divided into degrees, minutes, and seconds (1/60 of a minute).
How do these two relate? Without context, the other posters are right - it's apples and oranges. However, it's not unusual to use the linear measurement to describe the accuracy of an angular artifact. For example, it's very common for the accuracy of squares and angle blocks to be specified as a total deviation from the ideal over a fixed distance. This one specification supplies two important pieces of information. First, it indicates how flat the gauging surface is. Second, it indicates the maximum possible angular error (assuming that it is lowest at one end and highest at the other).
In your example, if we assume that +/-0.001 is inches, and that it is indicating a total error of +/-10 minutes of arc then I would suppose that the artifact is about 3 inches long (2.908"). Such an instrument would be inadequate for machinery setup. But, it could be used to mark wood if you like to cut to a line.
Hope it helps.
Ed Bennett snipped-for-privacy@ts-aligner.com http://www.ts-aligner.com
tommyboy wrote:

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snipped-for-privacy@ts-aligner.com wrote:

Interesting. I had always called it a millimeter <g>.
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Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

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alexy wrote:

OOPS! You're right. 0.001 meters is a millimeter. 0.001 mm is a micron. Nothing like being a few orders of magnitude off...
Thanks, Ed Bennett snipped-for-privacy@ts-aligner.com http://www.ts-aligner.com
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ok, GD&T is not just surface and vice versa. The control block format with words has a nomenclature of operator, operatees, etc. Just like grammar, its structure is immediately sensible, but is powerful using planes, immaginary and perfect references ...
The standard suface finish symbol is a one liner and its general format is given under
2: How to Read the Surface Finish Symbols, at http://www.jjjtrain.com/vms/engineering_surface_finish.html .
The documents all apply to this one liner symbol, and this symbol alone
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a meter is a meter. an inch is an inch. micro is a millionth;, theres one million micrometers or microns in a meter. nothing to do with a .001", a thousandth of an inch, or the imperial system. A thousandth of an ich is for those who don't think a 64th or 128th is really a good way to divide an inch. Its still the same inch in the first place. Just because its been divided by ten, then that can be divided by ten, etc.does mean it has anything to do with the metric system, micrometers or microns, which are just that long, but historically have been divided by 10, 10, 10 etc. Each time you divide by ten you just write down another digit, you don't need to track down a king for a new body part. a mil is the same thing as a 1000th of an inch .(001"). When you buy plastic you buy 6 mil plastic, it is 6 thousandths of an inch thick. mil as in milli, or thousandth, not million, not meteric. btw 4 mil plastic is really thin, don't use it. If you can rip it apart its probly not to code.
A 64th of an inch is 1/64" = .015625; which is no tenths of an inch 1 hundredths of an inch 5 thousandths of an inch 6 ten thousandths of an inch 2 hundred thousands of an inch 5 millionths of an inch
What is: most of 2 inches & 33/64ths thick subtract a half inch (well about 2/3 of a 16th less than that), shifted the majority of 7/16 to the right, and accounting for moiture content, and alowing for the thickness of five layers of paint on a tape measure? If I know it has to be tight to within say 3/128"; or say at exactly the point, but projected at 90 dergrees 4 inches away at thatis point, plus or minus 1/128", bu t when that
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Hi bent,
I definitely appreciate several of the links that you have posted. And, I appreciate the idea that fractions and decimals are just different ways to represent the same measures. Many people see a decimal representation like 0.015" and immediately think "that's an absurd tolerance for woodworking" but if they see 1/64" they say "that's appropriate for woodworking". In the angular example cited, I think that everyone will admit that 1/3 of a degree is significant for good joinery but when it's represented in terms of minutes of arc then suddenly people think it's absurd. Your point is well made and the allusion to the body parts of a king drives it all the way home.
I especially like your last point where you demonstrate the joys of doing fractional math. There are times when working in decimals is preferable!
However, I do believe that plastics which come in thicknesses below 0.006" (6 mil) have very practical and valid uses. ;-)
Thanks, Ed Bennett snipped-for-privacy@ts-aligner.com http://www.ts-aligner.com
bent wrote:

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