Micrometers

I was looking at electronic micrometers in the wish book today, and noticed that while a certain mike claims an accuracy to .0005 in, it has a
"resolution" of .00015. What is "resolution"?
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Stupendous Man wrote:

Meaning it counts .00000, .00015, .00030, .00045 ... so it will always show a number which is a nonnegative integer multiplied by .00015 if that makes sense.
GWE
--
Posted via a free Usenet account from http://www.teranews.com


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 11 Jan 2007 18:16:37 -0800, the renowned Grant Erwin

The above is correct. Forget what I said about half a tenth of a thou...
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
snipped-for-privacy@interlog.com Info for manufacturers: http://www.trexon.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 11 Jan 2007 17:53:50 -0800, the renowned "Stupendous Man"

Resolution is how closely you can read it (resolve the reading). In the case of a digital micrometer, a resolution of 0.00015 means that the display shows increments of half of a tenth of a thou.
Typically that means you can detect changes of that amount ("repeatability"), at least with everything else constant (temperature, battery condition etc.) but it is not guaranteed by that statement.
OTOH, accuracy means that (under the specified conditions) you should be able to glomp it onto an accurate gage block and it should read within half a thou of the correct reading (usually give or take the resolution, in the fine print, and typically with it just zero'd).
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
snipped-for-privacy@interlog.com Info for manufacturers: http://www.trexon.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It can display numbers to that small of an increment, but you could be anywhere 3 increments either side of it. More or less. So the measurement is very fine but might be very precisely wrong.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I have a supermicrometer... 0.0001" resolution... 0-12" jaws. made by pratt and whitney.
i

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 11 Jan 2007 21:01:49 -0600, Ignoramus16482

1 tenth over a 12" range? Wow. I hate to think what that sucker went for new...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

it weighs about 110 lbs... i can imagine it was expensive at some point.
i
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So if you measure 11.5 inches, and the next measurement is about .5 you use a cordless drill to bring it in? lol
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No, it measures differences in size (I think). You put in a known size close to what you need (like gages), note the position of the dials, then adjust the jaws to fit the part that you are measuring, and see how much you had to move.
This thing weighs 110 lbs.
i
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I'd hate to use it. Just heat from your hands while handling the frame will knock it so far out of kilter the measurements would be useless. It takes a lot of experience and a lot of patience to get accuracy from an instrument that large.
LLoyd
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
says...

Not to mention a lot of weight training. A supermic probably weighs 100# or more - it's a bench instrument.
http://www.atecorp.com/Equipment/PrattWhitney/SuperMicsml.JPG
Ned Simmons
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

that's exactly how it looks. I even have that strange electrical appliance pictured on top left of that picture (what is it?)
i
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ig,
That's an analog amplifier for the linear gage. The micrometer makes a nice paper weight without it in working order. Actually it's still useful without it functioning, but for repetitive high accuracy measurements, you need it. You would set a master in the micrometer, then zero out the gage. Now you can quickly take +/- comparitive measurements of workpieces.
With a functioning linear gage you can take comparative readings to whatever resolution/accuracy/repeatability of the linear gage. Usually 20 millionths. But more accurate ones are available for retrofit.
At those resolutions the flatness and paralellism of the anvils is an issue. You would need to check those with an optical flat and a monochromatic light source.
Then of course you need a very expensive set of master gage blocks with which to set it. Figure on those costing nearly the equivelent of the micrometer itself if you are wanting to cover the 12" range. Plus they degrade every time you use them, no matter how well you take care of them.
--

Dan

CNC Videos - <http://tinyurl.com/yzdt6d
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
    [ ... ]

    [ ... ]

    That reads motion of the anvil in whatever resolution is selected by a switch on it -- or is just a fixed sensitivity. The principle is that you set it to a standard, and zero the scale, and then it will show you how far over or under the desired size you are. I don't know the resolution on that one -- but it is probably good enough to display an microinch of difference.
    Enjoy,         DoN.
P.S.    My news server seems to be getting better, but I'm still losing     some articles -- so if you really need to communicate with me,     send me e-mail. :-)
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 11 Jan 2007 21:01:49 -0600, Ignoramus16482

At what temperature and humidity?
Gunner

"Deep in her heart, every moslem woman yearns to show us her tits" John Griffin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Dave Hinz wrote:

Sort of like measuring a peice of balsa wood with a micrometer. :-) ...lew...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Stupendous Man wrote:

You have 3 main factors in metrology: resolution accuracy repeatability (There are more, of course)
Resolution is how many graduations your "metering stick" has. Accuracy is how precise the graduation of your "metering stick" is. repeatability are the bounds of reading values you get when you repeatetly measure the same thing.
An pictorial example: Take a rubber band and draw lines at it every inch by eyeballing: The resolution will be one inch. The accuracy will be as good as you estimated the distances when you draw the lines The repeatability will be very bad, because the band stretches more or less, depending on the force when using it.
Nick
--
***********************************
*** Available now in NZ and AUS ***
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

noticed

Ahhhh... the old "precision vs. accuracy" thing...
Many years ago, I had a cheap vernier caliper that could measure to the nearest .01 in. That's the precision part. But whoever made the stupid thing obviously had no concept of the English system... If you measured a 1" piece, it would claim it was about .9 inches. That's the accuracy part.
When you say an instrument has, in your case, .00015 resolution (precision), it means that the reading you get is some integer multiple of .00015. In other words, the reading changes in .00015 steps. So, let's say you measure something and it reads: .63075. An accuracy of .0005 means that what you are measuring is actually somewhere between .63025 and .63125.
When a device has a high degree of resolution, it can often give you a false sense of accuracy.
Jerry
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks guys. That clears it up. When I worked as a machinist in a shipyard I once measured 34 inch propellor shafts at the 9 bearings. That was interesting. It took us 2 days to get them all uncovered, then jacked up the shaft and removed the lower bearing with a winch, then miked and re-assembled. It took the better part of a week to prove that after 30 years service they were fine. The guy and mobile machine that bored the new plastic "barrel" tailbushing after the seal was fascinating.
--
Stupendous Man,
Defender of Freedom, Advocate of Liberty
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.