How to Read a Micrometer

Hi, this is Kurt with Travers Tool Company. Today we're going to learn about micrometers and specifically how to read them. One of the things about micrometers is that the range of measurement is limited to only an inch. That's why there's so many different sizes available. Okay, so let's figure out how to use this thing or how to read it. First thing i'm going to mention is that this part with these numbers on it going around the back is the sleeve, and this is the thimble that I'm turning. Okay, so those are the only two parts I'm going to mention for now because those are the two we're going to be using, and notice when bring this all the way down, the zero and the line next to the zero line up with this line on the sleeve. So I'm not measuring anything, there's nothing in this micrometer, so that's measuring zero. I'm going to make one full revolution which is 25 thousandths. You see the 20 here, there's the zero, that's 25, so we know by the increments on the thimble that we want 25 thousandths, but we can also see right down in there, that little line, that tells us that we moved 25 thousandths. So one more revolution, you can see another line right down here, that means we move 50 thousandths, likewise that's 75, and here's hundred, and now you can just see that little number one just sneaking out from behind the thimble. So this measurement is actually one hundred thousandths, or one hundred thousandths of an inch. Okay, so let's get little bit more complex now. What if, so let's put it on the 10, so that the line next to the number 10 is lined up with this line. This is the line, if you haven't noticed already, should have said it earlier, this is the line we're going to read from with the lines and numbers on the thimble. So this is now, we know it's past hundred thousandths by the lines on the sleeve, and now we have 10 up here on the thimble, so that's 110 thousandths. Likewise, this would be 115 thousandths. We have the hundred thousandths down here, fifteen thousandths up there, that would be 117 thousandths, and so on. So let's just pick another number, and now what do we have? Just picked something randomly, here's 200 thousandths, there's the first mark, so that's 25 thousandths, so it's 225 plus 10, so 235. So that's measuring 235 thousandths. Let's get something bigger past half an inch, and there's the five, so that means the five is half inch or five hundred thousandths, we're going to put it right on that, which is the half thousandth, and do the same thing again. So there's 510 thousandths and so on. There's 525, and it just keeps going. So that's pretty basic, just using the numbers on the sleeve and the numbers on the thimble and adding them together to get you three places past the decimal. But now, you might have noticed all these lines back in here, and the numbers, you can see few of them up in here so far everything we've done is only three places past the decimal. What this does, these lines and numbers, is get you four places past the decimal. So now to explain what these lines are that go around the back. There's ten lines, they go from one to nine, and then the tenth one is actually zero. So here we have something, and as we discussed it before, you can see this goes past the five or half inch, but it's 500 thousandths. Here's the five to add to the 500 thousandths, so that would be 0.505, here's another line past the 5 so it would actually be 506. And then notice that this line isn't quite an alignment with this gauge line, but this one is. This is what goes the fourth place past the decimal. Now, when you're going to the fourth place, these numbers have no more relevance. Okay, so we already have the 0.506, and now we're gonna just tack onto the end of the 506. Since this line lines up, that's number one and that's what goes on the end of it, so this measurement is actually 0.5061. Let's just randomly pick another one. And here we can see the four, can't see any line past the 4, so it's below 25 thousandths, so here's the 10 so know this line is number 9. So it's 4.409, and then we'd have to go around the back and see which one lines up. You can't really see it from the angle of the camera, but the line that lines up is the 3. So this is 0.4—what did say, 0.4093. Again here's the 4, here's the nine, and here's the three. When measuring, the first place past the decimal is really tenth of an inch, but most machine shops go three places past the decimal, so that tenth of an inch would then be called one hundred thousandth of an inch. So, the second place past the decimal would be ten thousandths of an inch, or 0.01. Third place past the decimal would be 0.001, that would be one thousandth of an inch, and then the last place, the fourth place past the decimal, would then be one ten thousandth of an inch, which is mouthful, so since we're reading three places past the decimal, that would actually, in machine shop language, that would be called tenth. It wouldn't be called tenth of an inch because it's not, it would be tenth of thousandth, but it would be called tenth. So then 0.1234 would be 123 thousandths and four tenths. So let's actually measure something now. First thing is, how do you hold these things so that it's not just flimsy and just loose in your hand? First, you wrap your little finger around the frame and put the other part of the frame into your palm, take your ring finger and rest it on the back of the frame, and then use your thumb and index finger to turn the thimble. And that's real secure way to hold it in your hand while you're measuring something. So we're going to measure washer. Notice up here, I'm turning the thimble but the numbers aren't moving. This is friction thimble. It slips when the anvil and the spindle are measuring your workpiece, but then if you turn it the other direction it doesn't slip at all, and it'll open it. So let's get that measurement, and how you measure is you turn it so it's all the way in, and maybe move your workpiece around little bit just to make sure you have the smallest measurement you can get on here. So let's see what we have. Here's zero, there's one line, there's second line, and again each line is 25 thousandths, so two lines makes it fifty thousandths. So, I'm going to write down 0.05, then on the thimble we have another five and six, and this gauge line is between the 6 and the 7, so you always go to the lower number. Never ever ever to the higher number. So this is .056, and I'll write that down, and now I'm going to use the numbers around the back. So again for that last number, the fourth place past the decimal, we can see that this gauge line is in between the six and the seven. So now we go here and look for which one of these numbers lines up with any line on the thimble, disregarding the number up on the thimble, we're only paying attention to these numbers. So notice that that 5 lines up very well, where the 4 doesn't. The 4 doesn't line up with this line and the 6 doesn't line up with that line, but the five does. So that's what makes the fourth place past the decimal five. Here's little tip is as you're using micrometer, if you have to go from small measurement up to bigger measurement, just turning it this way is going to take you forever. So, couple of different ways you can speed that up: just kind of spin it like that and see how quickly that opens, or just running along your arm. Much easier than just turning it in your fingers. Thanks for watching. If you want to learn how to read calipers, check out this video.