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Engine Building Fundamentals: How to Use a Micrometer

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How to Use a Micrometer


00:00 - When it comes to building engines, the micrometer is one of the most common pieces of precision measuring equipment that we're going to be using.
00:08 Now I know that a lot of novice engine builders and mechanics really struggle with how to correctly use and read a micrometer, so in this module we're going to see exactly how to go about doing it.
00:19 Now while there are a few varieties of micrometer available, we're going to be focusing here on an imperial scaled vernier micrometer.
00:29 Now of course if you're using a digital micrometer, using the micrometer is relatively straightforward because the reading will be displayed digitally right in front of you.
00:41 However as we've already found out, we are going to need a range of different micrometers, in order to measure the different sizes we're likely to come across in the engine.
00:51 And since the digital micrometer is more expensive than a conventional mic, this is going to add greatly to the cost of your tool set.
00:59 Now here in front of me I have two micrometers, and these are a relatively cheap brand coming out of China, as we see with a lot of the common equipment we're going to be using these days in engine building.
01:11 And in front of me here I have a zero to one inch mic, and then I have a one to two inch mic.
01:17 This particular set goes all the way up to six inches, and we're simply going to select the micrometer that's suitable for whatever we're actually trying to measure.
01:28 Now with the micrometers there are two different types.
01:32 There is a vernier micrometer which is what we're going to be looking at today; this is able to measure down to four decimal places or 1/10,000 of an inch.
01:43 Or we can use a conventional or standard micrometer.
01:46 This eliminates the vernier scale and is able to measure down to 1/1,000 of an inch.
01:52 For today's lesson we will be looking at the vernier scale, however what we're going to learn will be applicable to a standard micrometer as well.
02:02 Before we get started using the micrometer, we're just going to have a look at the different components that make up the micrometer.
02:09 This is our one to two inch micrometer, and first of all we're going to have a look on the little plaque here; we can see that it's labelled 1-2", and we can also see that the precision of this micrometer is also listed; you can see it's listed at 0.0001 of an inch, or 1/10,000 of an inch.
02:29 I'm just going to flip it around so we can actually see the scale, and we'll just talk about the different components of the micrometer.
02:35 First of all, we have the frame which actually holds both ends of the micrometer.
02:41 The two measuring surfaces are between here and here, this particular component is known as the anvil, and this part which moves as we turn the screw thread is known as the spindle.
02:53 Here we have our measuring scale, which we'll be looking at in more detail shortly.
02:58 This particular component where our scale is written, is known as the barrel or sleeve of the micrometer.
03:05 Next we have the turning component which is known as the thimble.
03:09 And finally, at the end, we have our ratchet stop which is what we're going to be using for actually tightening the micrometer down on the component we're measuring.
03:19 We also have a positive stop which we can use to lock the micrometer once we have measured the component of interest.
03:27 Now that we've seen the different components of the micrometer, we're going to look at how we can actually use a micrometer to make a measurement.
03:35 Before we make any measurements, it's important to make sure that the measurement faces of the anvil and the spindle are both clean and free of dirt and debris, as these can have a dramatic effect on the accuracy of our reading.
03:50 Now what we're going to do is close down the micrometer, and just make sure that it is able to accurately read zero; so what we're looking at here, is that this zero line here lines up correctly and accurately with the zero mark on the barrel of the micrometer.
04:05 Now we're just going to talk about what each of these increments mean.
04:09 Now the increments on the thimble of the micrometer, represent 1/1000 of an inch, so every time we move past one of these increments, we're increasing by 1/1000 of an inch, so at this point we're reading 5/1000 of an inch.
04:25 Now every time we go through one full revolution, we come back to zero.
04:28 This means that the micrometer has incremented by 25/1000 of an inch.
04:34 And we can also see that as we do this, a new mark is now visible on the barrel of the micrometer.
04:42 So I'll just open it up a little bit further so we can see these marks a little bit more clearly.
04:47 So each of the marks along the barrel represents 25/1000 of an inch, and we can see that when we get out to four of these marks, we have a value of one, and this represents 1/10 of an inch, or 0.1 of an inch.
05:05 Now on the top of the scale here, we have our vernier marks, and these are going to be used to define our fourth decimal point, or our 1/10,000 of an inch precision, and we'll see how that works shortly.
05:19 Now that we know a little bit more about what these numbers mean, let's actually measure a component and see how this all works.
05:27 Okay, so now we're going to actually measure the width of this piece of aluminium, and you can see how I'm holding the micrometer; they're made to be used in your right hand, and while this is a little bit tricky because it is a small micrometer, you can see I've got my little finger just looped through the frame, and I'm using my thumb and forefinger on the spindle.
05:47 We can make coarse adjustments by using the thimble, but when we get to a point we're actually ready to make a measurement, it's important to use the ratchet stop, and this prevents us over tightening the micrometer.
06:00 So once we've got the micrometer tightened, and it's stopped moving, we can then lock it; and we can remove the component that we're measuring.
06:08 Let's now have a look at how we can calculate or measure the component that we've just put in our micrometer.
06:15 When you're learning to read a micrometer, it's valuable to write down each of the measurements as you read them, and then add them together; this makes it very clear exactly what the measurements are, and we're going to do that.
06:27 But let's have a look at what the numbers mean.
06:29 The first thing we want to look at it is how many numbers are visible on the barrel or sleeve of our micrometer.
06:35 Here you can see that we have the number three being exposed, and what this means is that we have a measurement of 0.3 inches.
06:45 Beyond that, though, we can also see we have three more increments exposed.
06:50 Remember each of those increments represents 25/1000 of an inch, so three of those represents 0.075 inches.
07:01 So we know that at this point we have 0.375 inches.
07:05 We can also see though, that, we've come up just beyond the number five; remember the thimble here represents 1/1000 of an inch, and we can see that we've gone a little bit past the five.
07:20 So we're somewhere beyond 5/1000 of an inch, and this is where the vernier scale comes in.
07:26 What we want to do is have a look at our vernier scale, and see which line comes closest to lining up.
07:33 We can see in this point, the six lines up correctly with our vernier scale, which is our fourth decimal point, or 0.0006 of an inch.
07:46 Let's write all those down and add them up so we can so we can see what our final value is.
07:50 When it comes to writing down the measurements from our micrometer, it's always best to look at them each individually, and then add them up.
07:57 We're going to start with our 1/10 of an inch measurement, which we can see here, remember we had our value of three, our measurement of three visible and that represents 0.3 of an inch.
08:11 I'm just going to add out to our four decimal places just so everything lines up when I've got the rest of our measurements listed.
08:20 Next, we have our little increments, and you'll remember each of those smaller increments represents 25/1000 of an inch.
08:27 We can see that three of these are visible, and that represents 0.075 of an inch, so let's write that down.
08:38 Now we can see that we've also gone past on our thimble here, we've gone past our five-thou mark, so we're going to also write that down.
08:50 And you'll remember that when we were looking at our vernier scale, on the top of the mic, we had 6/10,000 of an inch, so we'll write down our last value there as well.
09:01 Okay, so this represents the measurement from our micrometer, and what we need to do now is add up the different values.
09:09 So, we have 16/1000 of an inch; we have two fives here which add up to equal 10 so we're just going to carry the one; we have an eight, and a three.
09:19 So our final measurement is 0.3806 of an inch.
09:26 Like any piece of equipment, using a micrometer does take some practise to become competent with, but now you should understand the process to go through, and how to correctly read the numbers on the micrometer.

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