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Micrometer reading 101

S

SVcummins

Well-known Member

cvphoto67548.png


cvphoto67549.jpg


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.626 thousandths ??
 
I’ve got to go back to school again 😐. Apparently this isn’t
like riding a bicycle 🚲
 
With any micrometer look at the spindle that turns. It is usually 0 to.25 but in your case it should be 0-to 50. I see one mark in the middle between numbers. If you put 0 on the spindle at at number on the shaft part and start to turn it 0 going up by the time you hit 0 again it should be on the mark half way between the numbers. So the horizontal numbering would go every time it hits zero is .050. so you add the next numbers so the .698 is correct. .6 +.050 +.048+ =698. Hope that make sense. Most of the time I see ones in .025 increments. Mine are the .025.
 
Not quite the same, but in cleaning out a desk drawer in my shop yesterday, I found the slide rule I used in classes in 1960.

Nobody has use one of those since pocket calculator came about. Not sure if I'd even know how to use it, anymore.
 
(quoted from post at 14:42:09 12/18/20) Looks like 0.647 from here.
Click to expand...

Roger has it right.

I didn't catch that the divisions were 0.050", I expected the more common 0.025"
 

Maybe this will help. It looks like the Thimble is marked in .0005 increments between the .001 increments to me, from what I see in your photo. The .025 increment marks below the line on the sleeve should match 1 full revolution of the thimble for each. So .100" (4 full revolutions of the thimble) between each number on the sleeve.

mvphoto66843.jpg
 

We need a better picture of the thimble to confirm what the divisions are for sure. Show the 0 and the number either side of it, then we can see if it is marked in .0005 increments.
 
And that could be correct also. The machine shop I worked at calibrated everything every other month. So the calibrations of each could be in question.
 
Hello s cummins,

It's reading 0.771 minus the digital reading. This means that the zero is off,

Guido.
 
Hello svcummins,

I read it wrong! Its reading .001 less the 0.700. The zero is still off. Use the slip function to get it to zero. There is a lock so it does not move, and some wrench to turn it to zero it.

Mine has a c wrench that turns it,

Guido.
 
Did you get a standard with it so you can read what it is supposed to read to get the idea of it?
 
If it only takes two turns to go a tenth of an inch, then I agree it is .6975. However, if it takes four turns to measure one tenth of an inch, then I would say it is close to .6987

Lon
 

To answer that we need to see more of the numbers on the thimble to see what the numbers are and how many marks between them. Or SV needs to tell us how many turns it takes to go from one number on the sleeve to the next.

The .012 (+/-) bust between the mic and caliper would be a concern to me and could be a number of things. Not knowing what he is measuring, it may not matter in the end.
 
IF thimble is rotating down and the long lines are .001 apart then the short line are .0005 or 1/2 of a thousands. no lines line up. it is half way between .001 and .0015 or 1 and one quarter of a thousands. or .00125. therefor is is that much short of .700 . .69875. I sent 30 years working as a tool and die maker on parts within a + or - .0005. Been retire 20 years so I could be wrong
 
Almost impossible to get a good picture but now I think I have it little lines on the barrel are 25 thousandth and the big lines are 50 thousandths then hundred thousandths then the thimble is in one thousandth
 
(quoted from post at 23:39:59 12/18/20) I am even more confused than when I starred 😐.
<img src="https://www.yesterdaystractors.com/cvphotos/cvphoto67614.jpg">
Click to expand...

How many complete turns of the thimble does it take to move from the #5 line on the barrel (aka sleeve) to the #6 line? How many lines, total, are there around the thimble?
 
(quoted from post at 00:09:38 12/19/20) The thimble is .25 thousandths per revolution or one little
mark on the barrel
Click to expand...

Thanks, the thimble moves 25 thousandths per revolution. What is the total number of marks, long and short, around the thimble? 25 or 50. From counting visible marks on the thimble in your pictures, it looks like it may be 50, in which case the thimble is graduated for one-half thousandths.
 
(quoted from post at 16:07:43 12/19/20) Each little mark on the thimble is - 500 a hundredth or half a thousandth
Click to expand...

Thank you for clearing this up, the small marks are each 1/2 thousandth as I thought. The packaging may say graduated in .001" but the thimble of the one you have is graduated on .0005" increments. So your reading that started this was about .6985", .0015 less than .700. The angle of your picture may be throwing that reading off a bit as compared to looking at it square on, in hand.

As for the .010" difference between the caliper and mic, it could be several things; calibrations may be off, piece you were measuring might be out of round, operator "feel" was likely different, changing temperature, for somethings. Even the temperature from your hand can make a difference. The calibration shop I take things to won't do a calibration until the tool sets in their lab for 24 hours so it is the same temp as the calibration gear.


mvphoto66873.jpg
 
The usual mike barrel is threaded inside at 40tpi & has 25 gradations on the thimble(as this one has). Therefore each mark becomes 1"divided by (40X25) equals 1 thou. One full turn of the thimble is 25 gradations & moves 1/40th of an inch.
I'd very much doubt that a cheap mike was graduated in 1/2 thou's, which would mean the barrel was threaded at 80TPI?
 
Why can't we edit our own posts?
I just noticed that the General micrometer shown in Iim ME's post is a different one than the OP showed. We need to see how many gradations are in one full turn of the OP's thimble to verify the .6975 answer.
 

The edit feature does not work presently, due to issues between classic and modern views I believe, and has been discussed many times.

I already asked that question and SV has answered it. One turn moves 25 thousandths. The last picture of a General #102 mic is one I posted it to show the difference in the thimble graduations. That is one I consider graduated in thousandths on the thimble, with 25 marks around the circumference.

From the picture of the packaging I am guessing it is a General, that is not confirmed. General provides some good tools, at a reasonable price, which meet the needs of many. I have some of their tools, so I am not bashing them.

Some research of images reveals General had some, like SV's, with 50 marks around the thimble (with travel 25 thousandths per revolution). I call that graduated in .0005", even though packaging says graduations are .001" (Its not graduated in millimeters). Research also found General also had some carbide faced mics at one time. They may not have actually produced all the mics they sold. They may have had some branded from other sources, which could axplain the differences over the years. Many brands of "cheap" mics have .0005" graduations and carbide faces, so price doesn't always control what you get. Many are surprisingly accurate, at least in the beginning. How accurate they, or any mic, remain over the years can only be checked by regular calibration. I have seen "cheap" mics pass calibration and "expensive" ones fail.
 
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