Precise Measurment with a Caliper or Micrometer

Transcription

1 For Good Measure: Precise Measurment with a Caliper or Micrometer by Steve Bodofsky As seen in Magazine

2 This program has been designed by the Automatic Transmission Rebuilders Association (ATRA) to be used by qualified automotive transmission technicians. Since the circumstances of its use is beyond ATRA s control, ATRA assumes no liability for the use of such information or any damages incurred through its use and application. Nothing contained in this program is to be considered contractual or providing some form of warranty on the part of ATRA. No part of this program should be construed as recommending any procedure which is contrary to the vehicle manufacturer s procedures. This program contains copyrighted material belonging to ATRA. No part of this program may be reproduced or used in any form or by any means graphic, electronic or mechanical, including photocopying, recording, electronic, or information storage-and-retrieval systems without the express written permission from ATRA. ATRA and the ATRA logo are registered trademarks of the Automatic Transmission Rebuilders Association. Public exhibition or use of this material for group training or as part of a school curriculum, without the express written permission of ATRA, is prohibited by law. For information on using this material for independent training programs, contact ATRA at (805) ATRA. All Rights Reserved. Page ATRA. All Rights Reserved.

3 Contents Introduction... 4 Don t Waste Your Time... 5 The Parts of A Vernier Caliper... 7 Zero the Caliper... 8 Measuring with a Vernier Caliper Outer Diameter Inner Diameter Depth Step Height Reading a Vernier Caliper Standard Caliper Standard Caliper; Decimal Imperial Scale Standard Caliper; Metric Scale Standard Caliper; Fractional Imperial Scale Dial Caliper Digital Caliper Using a Micrometer Parts of a Micrometer Holding Your Micrometer Zero Your Micrometer Measuring Thickness Reading the Micrometer Choosing the Right Size Mic Reading the Scale Imperial (Inches) Measuring with a Mic Imperial (Inches) Reading a Metric Mic Test Your Measurement Skills Conversions, the Easy Way ATRA. All Rights Reserved Page 3

4 Introduction While rebuilding a 4T60E transaxle, you notice the pump rotor splines are worn; you ll need to replace the rotor. That s okay: You have several good used rotors on the shelf. But they come in different thicknesses. How can you tell which one you need? You re going to have to measure the rotors to find one that s the correct thickness. Sounds easy, doesn t it? But the thickness variations are slight; sometimes as little as a few thousandths of an inch. A tape measure just isn t going to cut it you re going to need a more accurate way to measure thickness. You re going to need a vernier caliper or micrometer. Having the right tool is easy enough: Calipers and micrometers are available from just about any tool or parts store. The hard part is reading them. There are a number of reasons for this, not least of which being that they come in many different forms and versions. In this booklet, we re going to look at a few different styles of caliper and micrometer, to learn how to choose them and how to use them. Page ATRA. All Rights Reserved.

5 Introduction (continued) Don t Waste Your Time Before you get too far into this program, I m going to make a simple suggestion to you: Don t bother. That s right don t waste time trying to learn how to use all the different types of vernier calipers and micrometers. You don t need to know. There s an easier solution: Buy a digital caliper. Let s face it: Fixing transmissions is critical work, but it s not rocket science. As long as you re within a thousandth of an inch or a hundredth of a millimeter you re probably going to be close enough. And a digital caliper will give you that level of accuracy, without forcing you to spend a lot of time learning to interpret a convoluted scale that s too tiny to be read without a magnifying glass. Figure 1: To provide an adequate demonstration for this booklet, I purchased three new calipers. Total cost: just under $47. The digital itself was just $9.45 plus shipping. Price? I just bought these three new calipers (figure 1): a standard caliper, a dial type, and a digital, from the Discount Machine Shop store on Ebay: The total including shipping was just under $47, and they were here in less than a week. The digital caliper alone was $9.45 plus shipping. Is it as accurate as the more expensive models? Hard to be sure, but it s probably more than accurate enough for your needs. I compared it to a micrometer, and the digital caliper appeared to be accurate to within ". In fact, all three 2007 ATRA. All Rights Reserved Page 5

6 Introduction (continued) Don t Waste Your Time (continued) calipers were within about a thousandth of an inch of one another. Accurate enough for any auto repairs you re likely to run into. And a digital caliper gives you a simple, digital readout, in either inches or millimeters, at the press of a button (figure 2). No trying to interpret the scratches on a scale or adding the numbers: Just read and go. At about $20 (including shipping), it s really a smart choice. Figure 2: A digital caliper is certainly the easiest to use. The display is easy to read, and you can switch between Imperial (inches) and Metric at the touch of a button. Of course, some people just prefer to learn, even if it isn t something they re necessarily going to use. For them, we ll look at how to use all of the more common types of caliper and micrometer. We ll start with calipers, beginning with the basics that are common to all calipers. Page ATRA. All Rights Reserved.

7 The Parts of a Vernier Caliper FOR GOOD MEASURE There are several parts common to most vernier calipers (figure 3). You ll need to know these terms so you ll understand the explanations for how to use them. 1. Outside Jaws for measuring the outer diameter of a component. 2. Inside Jaws for measuring the inside diameter of a component. 3. Depth Probe for measuring depth. 4. Main Scale/Fixed Scale usually provides measurements in Imperial (inches) or Metric units. 5. Vernier Scale/Moveable Scale slider that indicates measured size on the scale. 6. Adjustment Roller allows for easy movement of the jaws; not all calipers have this. 7. Locking Screw/Lever locks the caliper jaws in place to make it easier to read the measurement ATRA. All Rights Reserved Page 7

8 Zero the Caliper Before you begin a measurement with any type of caliper or micrometer, your first step is to zero it. This is an important step to assure accuracy, and should be repeated before each measurement. You can also use the zeroing feature to measure the difference between two components. With the jaws measuring the first component, zero the caliper. Then measure the second. The measurement on your caliper is the difference between the two components. Here s how to zero your caliper: Open the caliper. Slide it gently back to the fully closed position. You may have to do this a couple times to be sure it s closed all the way. Check the measurement on the scale. With the jaws fully closed, the scale should read zero. To zero a digital caliper, just press the zero button (figure 4). Figure 4: Zeroing a digital caliper is easy: Just press the zero button and you re ready to take your measurement. Page ATRA. All Rights Reserved.

9 Zero the Caliper (continued) FOR GOOD MEASURE To zero a dial caliper, loosen the locking screw, and rotate the dial until the needle is pointing to zero (figure 5). Figure 5: To zero a dial caliper, loosen the lock screw, and rotate the dial until the needle lines up with zero. Make sure you re looking straight at the dial when adjusting or reading it, to prevent parallax errors. Dials such as these are subject to parallax errors; that is, slight errors created when you view the dial from different angles. To avoid parallax errors, always keep the dial squarely in front of you when reading the measurement; never read it from an angle. To zero a standard caliper well, you can t; at least, not for any I ve ever seen. All you can do is compensate for the inaccuracy. Check how much it s off, then subtract that amount from (or add it to) your final measurement to get an accurate reading ATRA. All Rights Reserved Page 9

10 Measuring with a Vernier Caliper Outer Diameter Once you have your caliper zeroed, you re ready to begin your measurement. Vernier calipers are capable of making four main kinds of measurements: Outer Diameter Inner Diameter Depth Step Height Let s look at each of these measurements: Outer diameter is probably the most familiar use for a caliper. You use the outside jaws to measure the distance across the outside edges of a component. For this demonstration, we re going to measure the outer diameter of a copper pipe fitting; here s how: 1. Zero your caliper. 2. Open the jaws, and then close them gently around the outside of the component (figure 6). Not too tight: You don t want to distort the component or your caliper. In most cases, you should just about be able to move the component, while feeling it drag firmly against the jaws. Figure 6: To measure the outer diameter of a component, apply the outside jaws gently around the widest part of the component. Not too tight! You don t want to crush anything, or screw up the measurement. Page ATRA. All Rights Reserved.

11 Measuring (continued) FOR GOOD MEASURE Outer Diameter (continued) 3. Wiggle the component or your caliper slightly as you slide the jaws around it, to make sure you re measuring at the widest spot, and it s sitting squarely between the jaws. 4. Once you have the jaws securely in place, lock them with the screw or lever (figure 7). Figure 7: Once you have the component centered and the jaws in place, tighten the lock screw to hold your measurement steady. 5. Read the measurement on the scale ATRA. All Rights Reserved Page 11

12 Measuring (continued) Inner Diameter The inside jaws allow you to measure the inner diameter of most openings to a depth of about a half inch. Notice the small cutout on the inside edge of the jaws (figure 8). This allows for a slight ridge, such as the remnants from a pipe cutter. The cutout avoids the ridge, allowing you to measure the unmarred area of the opening. Figure 8: The small cutout on the back edge of the inside jaws allows you to measure without worrying about the ridge along the edge of the opening. Page ATRA. All Rights Reserved.

13 Measuring (continued) FOR GOOD MEASURE Inner Diameter (continued) To measure the inner diameter: 1. Zero the caliper. 2. Slip the inside jaws into the opening. 3. Open the jaws until they contact the sides of the opening (figure 9). Not too tight: You don t want to distort the component or your caliper. In most cases, you should just about be able to move the component, while feeling it drag firmly against the jaws. Figure 9: Slide the inside jaws into the opening, and open the caliper until the jaws contact the surface. Wiggle the component and your caliper to make sure you re measuring at the widest point in the opening. 4. Wiggle the component or your caliper slightly as you slide the jaws around the opening, to make sure you re measuring at the widest spot, and the jaws are sitting squarely on the sides. 5. Once you have the jaws securely in place, lock them with the locking screw or lever. 6. Read the measurement on the scale ATRA. All Rights Reserved Page 13

14 Measuring (continued) Depth The depth probe on the opposite end of the caliper makes it easy to measure the depth of a hole or channel. When measuring depth, always zero the caliper using the depth probe. That is, open the caliper, and then gently press the depth probe down against a completely flat surface, until your caliper bottoms out (figure 10). Then zero the scale. Figure 10: When measuring depth, always zero against your depth probe. There could be a slight variation between the depth probe and the regular jaws. The reason for this special zeroing procedure is simple: There may be a slight variation between the jaws and the depth probe. Zeroing against the depth probe eliminates that error. To measure depth: 1. Zero the caliper. 2. Hold the caliper on the flat surface you re measuring against (figure 11). Figure 11: To measure depth, hold the end of the caliper against the object you re measuring. Page ATRA. All Rights Reserved.

15 Measuring (continued) FOR GOOD MEASURE Depth (continued) 3. Open the caliper until it rises away from the surface, and is sitting on only the depth probe (figure 12). Figure 12: Open the caliper until it rises away from the component onto the end of the depth probe. 4. Gently press down against the depth probe until the caliper just bottoms again (figure 13). Figure 13: Gently press down against the depth probe, until the caliper just contacts the component again. 5. Lock the caliper in place with the locking screw or lever. 6. Read the measurement on the scale ATRA. All Rights Reserved Page 15

16 Measuring (continued) Step Height This is the one measurement you might be completely unfamiliar with. But there are times when it could come in handy. Here s what the step height measurement is: With the jaws closed, the top of the fixed jaw and the moveable jaw are aligned. So, if you place the caliper against one flat surface, the measurement will display the height to the top of the moveable jaw (figure 14). Figure 14: The ends of the fixed and moveable jaws align when the caliper is closed, so you can use the caliper to measure step height, too. While not a particularly common procedure for the automotive repair industry, there may be times when this could come in handy. Once you re comfortable handling a caliper, you re ready to learn to read the scales. Page ATRA. All Rights Reserved.

17 Reading a Vernier Caliper Standard Caliper The term standard is a horrible misnomer for this type of caliper, because there s very little that s standard about it (figure 15). Some read in thousandths of an inch; others read in fractions, usually down to 1 /128 th of an inch. Some have a metric scale, but not all. A Figure 15: The standard caliper comes in all different forms and formats, making the term standard a huge misnomer. Here are two different types of standard caliper: one that reads in thousandths of an inch and hundreds of a millimeter (A), and a second that reads in fractions of an inch (B). B If your vernier caliper reads in fractions, the best thing you can do is give it to someone you really don t like. Using this type of caliper requires not only reading the different scales, but also adding fractions; that means finding a common denominator and adding the numerator. Then you ll still probably have to convert your measurement to decimals. Not an easy task overall, with lots of steps for a mistake to creep into your measurement ATRA. All Rights Reserved Page 17

18 Reading a Vernier Caliper (continued) Standard Caliper; Decimal Imperial Scale The better choice is a vernier caliper that measures in decimals; that is, thousandths of an inch and hundredths of a millimeter. Let s look at what each scale means, beginning with the Imperial (inch) scale: The Main or Fixed scale breaks each inch into 10 numbered graduations (figure 16); each graduation equals 1 /10 th of an inch, or 0.1". Each of those graduations is broken into four smaller graduations, each equaling 0.025". Figure 16: Each inch on the fixed scale breaks into 10 large divisions, or 0.1". Those graduations break into four smaller graduations, equaling 0.025" each. Figure 17: The vernier has 25 graduations on the top (inches) scale. These allow you to refine your measurement. Look for the one that aligns perfectly with a graduation on the fixed scale: That s the measurement, down to 0.001". Notice that the adjustment jaw, or vernier, also has graduations: 25 on the Imperial scale (figure 17). Those divisions allow you to refine your measurement down to 0.001". Let s measure the width of this air conditioning feeler gauge and see how to use these calipers: With the feeler gauge held in place, the measurement appears to be about half an inch (figure 18). But look closer: The zero line on the vernier is just a tiny bit shy of the halfinch mark. That indicates this feeler gauge is less than half an inch but how much less? Page ATRA. All Rights Reserved.

19 Reading a Vernier Caliper (continued) Standard Caliper; Decimal Imperial Scale (continued) FOR GOOD MEASURE Figure 18: For this measurement, the zero lines up with the third graduation after 0.4 ; that s 0.475". The graduation on the vernier that aligns with the graduations on the fixed scale is 21, so we add 0.021" to 0.475". The total measurement is 0.496". This is where those extra 25 graduations come into play. Look along those 25 graduations: Find the one that lines up precisely with a graduation on the fixed scale. Look closely: Some will appear closer than others. You should find a range of about five graduations that look awfully close choose the one in the middle. In this case, the graduation that lines up the best seems to be 21, or 0.021". Now we add the two measurements: 0.475" from the fixed scale 0.021" from the vernier scale 0.496" actual measurement So the measurement is 0.496" based on the standard decimal caliper. How accurate is that? Let s compare it to the digital caliper (figure 19). Figure 19: A quick check with the digital caliper reveals our measurement was accurate to within "; not bad for counting a bunch of lines on a scale! Not bad. According to the digital caliper, the feeler gauge is "; that s within ". Can t ask for much better accuracy than 2007 ATRA. All Rights Reserved Page 19

20 Reading a Vernier Caliper (continued) Standard Caliper; Metric Scale that! Now we ll look at the bottom scale on the standard caliper: This is the Metric scale (figure 20). Each graduation on the fixed Metric scale is equal to one millimeter. The numbers Figure 20: Each graduation on the fixed Metric scale is equal to one millimeter. The graduations on the Metric side are also broken into 10 divisions, with each broken into 5 smaller divisions. So each small division on the vernier lets you measure down to 0.02 millimeters. indicate centimeters, or ten millimeters. Notice the graduations on the Metric side of the vernier: It has 10 numbered graduations, and each numbered graduation is divided into five smaller graduations. The numbered graduations are tenths of a millimeter; the smaller graduations are 0.02 millimeters. These graduations work the same as the ones on the Imperial scale. Let s measure the feeler gauge again and see how the Metric scale works: With the feeler gauge in place, the zero on the vernier scale is just over two millimeters past the 10-millimeter mark on the fixed scale (figure 21). So the feeler gauge is just over 12 Figure 21: The zero on the Metric scale is just a little over two graduations past 10 millimeters, so the actual measurement is just over 12 millimeters. Page ATRA. All Rights Reserved.

21 Reading a Vernier Caliper (continued) millimeters. But how much over? FOR GOOD MEASURE Just as before, look for which graduations on the vernier line up with the graduations on the fixed scale (figure 22). It looks like the graduation at number 6 is in perfect alignment Figure 22: Now when we examine the graduations on the vernier, we see the graduation at number 6 is in perfect alignment. So the measurement is 12.6 millimeters. with the fixed scale. That means this feeler gauge is exactly millimeters across. How does that compare with our previous measurement? If we divide 12.6 by 25.4, we get "; pretty close to the " we measured with the digital caliper. Figure 23: To measure the feeler gauge in millimeters using the digital caliper, all we need to do is press the inch/mm button. Our measurement was right on the money ATRA. All Rights Reserved Page 21

22 Reading a Vernier Caliper (continued) Standard Caliper; Fractional Imperial Scale To confirm it with the digital caliper, we just press the inch/ mm button and measure it again (figure 23). Hmm millimeters. Right on the money! If you re still insistent on learning how to use a fractional caliper, here s how to read the scale (figure 24). This caliper has two basic scales: one in 16 ths of an inch, the other in Figure 24: This fractional caliper provides measurements in 16 ths and 32 nds of an inch. And the vernier scale on the 16 ths side lets us refine our measurement down to 1 /128 th of an inch. 32 nds of an inch. The 16 ths scale has eight additional divisions on the adjustable jaw, allowing you to refine your measurement down to 1 /128 th of an inch. Let s measure that feeler gauge again (figure 25): At first glance, it appears to be an even half inch. But a closer ex- Figure 25: At first glance, it appears that the feeler gauge is 1 /2" wide. But a closer look reveals that the last graduation on the vernier scale is lined up with the fixed scale, so it s actually 1 /128" less than 1 /2". Several mathematical steps later, we discover that it s actually " wide. Page ATRA. All Rights Reserved.

23 Reading a Vernier Caliper (continued) FOR GOOD MEASURE amination reveals that the second to the last line on the vernier jaw is the one that s actually lined up with the fixed scale. That means this shim is actually 1 /128" less than 1 /2". Now let s do the math. Remember, to add or subtract fractions, we must first find a common denominator: 1 /2 = 64 / /128 1 /128 = 63 /128 So the feeler gauge is 63 /128" wide. Great; but how close is that to our earlier measurement? To figure that out, we have to convert the fraction to decimals, by dividing the numerator by the denominator (now do you see why you don t want a fractional caliper?) = So the gauge is " wide. How does that compare with our earlier measurement? It s within 0.003", which isn t bad, considering what a cheesy caliper it is. And, of course, there s always something lost when rounding the calculation. Not too shabby, all things considered. But was it worth the effort? Probably not: especially for a measurement that was still off by about 0.003". For my money, I d rather go with the digital, and avoid the confusion and the inaccuracy ATRA. All Rights Reserved Page 23

24 Reading a Vernier Caliper (continued) Dial Caliper Dials such as these are subject to parallax errors; that is, slight errors created by the angle from which you look at the dial. To avoid parallax errors, always keep the dial directly in front of you when reading the measurement; never read it from an angle. Most dial calipers display either inches or millimeters; only a few display both. That s because the conversion ratio would create a problem for using them. Let s look at how to read the dial, and you ll see why. The fixed scale is broken into 10 graduations per inch (figure 26). As you move the vernier, the needle on the dial makes a complete revolution for each 1 /10 th of an inch it travels. And the dial is broken into 100 graduations. So each graduation on the dial equals 1 /1000 th (0.001) of an inch. Figure 26: The fixed scale on the dial caliper is broken into tenths of an inch, and each graduation on the dial equals 0.001". The problem with having a dial caliper that reads in both inches and millimeters is there s no way for a complete rotation to equal both 1 /10 th of an inch and a useful Metric equivalent. So when measuring, only one of those measurements can relate to a compete rotation of the needle. The other would be only a part of a revolution, and the zero position would continue to change, depending on the size of the item being measured. Page ATRA. All Rights Reserved.

25 Reading a Vernier Caliper (continued) FOR GOOD MEASURE The only way to allow both measurements to zero at the same point would be to change the gearing in the dial; possible, but a much more complex and costly construction. So, if you insist on going with a dial caliper, you should probably get two: one Imperial (inches) and one Metric. Now let s try the dial caliper, and see how it compares with the others: As you can see, the fixed scale indicates about 0.5" (figure 27). But the dial is at 96; right near the end of the scale. So this measurement is just under 0.5". Figure 27: Measuring the same feeler gauge shows the fixed gauge right near the half-inch mark. But the dial is at 96, which indicates the feeler is just under a half inch: 0.496" to be precise. The previous measurement on the fixed scale is 0.4", or 0.400". The 96 is 0.096", so we add 0.096" to 0.400" and get 0.496"; as we said, just under 0.5". The digital scale measured the feeler gauge at ", so the dial caliper was within "; again, not a bad level of accuracy ATRA. All Rights Reserved Page 25

26 Reading a Vernier Caliper (continued) Digital Caliper We could get into the whole process of measuring the feeler gauge again, but to be honest, there s no real reason to do so. Once you use the procedures to fit the item to the caliper s jaws, the measurement appears digitally on the display (figure 28). You want Metric? Press the button, and it s Metric. Press again and it s back to Imperial (inches). There s nothing we can add that you didn t learn back in 3 rd grade. Figure 28: The procedure for using a digital caliper is the same as for the other styles; from there, the measurement appears digitally on the display. So, in general, each of these calipers provides an accurate measurement, all within about a thousandth of an inch or less of one another (except the fractional caliper, and remember, you re going to give that to someone you dislike!) But when it comes to accuracy, ease of use, and price, these days it s hard to imagine any reason to go any way but digital. Next we ll look at how to use a micrometer, and compare its accuracy to a caliper. Page ATRA. All Rights Reserved.

27 Using a Micrometer Figure 29: This is what we think of when someone says micrometer : an outside mic used to measure thickness. There are many other types of mic, but most are read in the same manner. When it comes to accurate measurement, the first tool most people think of is a micrometer. A standard micrometer allows you to measure accurately down to as small as 1 /10,000 th of an inch, using a simple technology that s been around for as long as anyone can remember. When we use the term micrometer, we re actually talking about a wide range of devices used to take precise measurements. There are outside micrometers and inside micrometers; depth micrometers and bore micrometers; and all sorts of specialty micrometers. Some have interchangeable anvils, to offer a wider range of measurements. They have micrometers that measure in Imperial units (inches) or Metric, and are even available in digital formats. But when most of us think of a micrometer, we think of the standard, outside micrometer, or mic (pronounced myk); the one that looks like a C-clamp (figure 29). It s designed exclusively to measure thickness. In this program, we re going to cover the basics of using an outside mic. While the actual handling of other styles of mic may vary, the method of reading the mic itself is usually pretty much the same ATRA. All Rights Reserved Page 27

28 Parts of a Micrometer To discuss how to use a micrometer, it s first helpful to have the component parts defined, so we can speak the same language (figure 30): A. Anvil B. Spindle C. Frame D. Locknut E. Sleeve, Barrel or Hub F. Thimble G. Ratchet or Friction Screw H. Vernier I. Standard Rods or Standards Page ATRA. All Rights Reserved.

29 Holding Your Micrometer FOR GOOD MEASURE Figure 31: The correct way to hold an outside mic is to hold it in one hand like this, leaving your other hand free to control or adjust the object you re measuring. Here s the correct way to hold a micrometer for use (figure 31). This is important for two reasons: 1. It enables you to adjust the micrometer with one hand, while holding the object you re measuring in position with the other. 2. It gives you the opportunity to act all superior and condescending when you see someone who doesn t know the right way to hold a mic. ( Where did you learn how to use a micrometer? Sesame Street? ) Okay, maybe there s really only one good reason, but you gotta admit, you re going to be thinking about that second one the next time you see someone holding a mic the wrong way! 2007 ATRA. All Rights Reserved Page 29

30 Zero Your Micrometer While a micrometer tends to be a bit more stable than a caliper when it comes to size, it s still important to zero your mic before you use it. In most cases, you ll only have to zero it once at the beginning of your measurement session, as opposed to a vernier caliper, which you should check before each measurement. To zero the micrometer: 1. Open the mic, then slowly close it all the way. If you aren t well versed in handling a mic (which you probably aren t, or you wouldn t be reading this article) use the friction screw to close it. Always rotate the shaft slowly when closing the mic. Even though you re using the friction screw, the momentum of the shaft can be enough to overtighten it if you turn it too quickly. 2. Once you have the mic closed all the way, check the scale: the zero on the thimble should line up with the zero on the sleeve (figure 32). Figure 32: Once you have the mic closed all the way, the zero on the sleeve should line up precisely with the zero on the thimble. Page ATRA. All Rights Reserved.

31 Zero Your Micrometer (continued) FOR GOOD MEASURE 3. To zero the mic, use the spanner wrench that came with the mic to rotate the sleeve (figure 33). Then recheck it. You may have to try this a few times to get your mic zeroed properly. Figure 33: To adjust the mic, use the spanner wrench that came with it to rotate the sleeve, until the zero lines up with the zero on the thimble. Rotating the sleeve a small amount can be tricky; it can take a lot of force to get the sleeve to start turning, and once it starts it may turn too far. To get it zeroed, you may find it easier to rotate the sleeve farther out, and then rotate it back to zero. Some mics don t have an adjustable sleeve. If yours doesn t, you won t be able to zero it; in that case, make a note of how far it s off, and then add or subtract that from your measurement ATRA. All Rights Reserved Page 31

32 Zero Your Micrometer (continued) Some mics don t close. For example, mics that measure between 1" and 2" or 2" to 3" don t close all the way (figure 34). Figure 34: Some mics never close all the way, so you can t zero them the same way you would a small mic. You ll need something to fill in the space you ll need a standard. To zero those mics, you ll need a standard rod, or standard. Standards are steel rods that are exactly a certain length (figure 35). In this case, we have a 1" standard and a 2" standard. To zero the 1" 2" mic: Figure 35: Standards are metal rods that are calibrated in size to allow you to zero your micrometers. The 1" standard is for zeroing the 1" 2" mic; the 2" standard is for zeroing the 2" 3" mic. Page ATRA. All Rights Reserved.

33 Zero Your Micrometer (continued) FOR GOOD MEASURE 1. Slip the 1" standard between the anvil and the spindle (figure 36). Figure 36: Hold the standard in place, just as though you were measuring it. Once the standard is firmly between the anvil and spindle, zero the mic. 2. Close the mic gently against the standard. 3. Adjust the mic to zero. To zero the 2" 3" mic, use the 2" standard ATRA. All Rights Reserved Page 33

34 Measuring Thickness To measure the thickness of an object with an outside mic: 1. Zero the mic. 2. Open the mic far enough to allow the object you re measuring to fit easily between the anvil and the spindle. 3. Gently close the mic, until it fits firmly between the anvil and the spindle (figure 37). Wiggle or rotate the object to make sure it s sitting squarely between the two measuring surfaces. Figure 37: Gently close the mic around the object you re measuring, while wiggling the object between the measuring surfaces to make sure it s sitting squarely in place, and isn t cocked or out of position. 4. Once you have the mic adjusted to the object, lock the spindle with the locknut. Now you re ready to read the mic. Page ATRA. All Rights Reserved.

35 Reading the Micrometer Virtually all micrometers are read the same way. The only real differences between them are: Maximum size or scale Units of measure Vernier scale By maximum size or scale, we re talking about the range of the mic. If the mic you need to use measures between 2" 3", the first digit of the measurement will usually be a 2. If it s a zero-to-one inch scale, the first digit will usually be a zero. Units of measure is either Imperial (inches) or metric. We ll look at how to read both types of scale. The vernier scale is the important one: Some mics have them; others don t (figure 38). Figure 38: Some mics have a vernier scale; others don t. The vernier scale allows you to resolve your measurement down to 1 /10,000 th of an inch, or 1 /1000 th of a millimeter ATRA. All Rights Reserved Page 35

36 Reading the Micrometer (continued) The vernier scale is an additional scale that allows you to refine your measurement down to 1 /10,000 th of an inch, or 1 /1000 th of a millimeter. Our Imperial (inches) mic has a vernier scale, so we ll cover how to use it. If your mic doesn t have a vernier scale, you can approximate the finer measurement by looking at the position of the scale on the thimble in relation to the zero point on the sleeve. But you probably won t need to; that s an awfully precise measurement more so than you should ever need, unless you re a machinist. If you do need to resolve your measurement that far, you should probably get a mic that s either digital or offers a vernier scale. They aren t that expensive if you know where to look: Here s a set of three that I bought for these pictures (figure 39). They cost just $36 including shipping, from JTS Machinery & Supply Company; Figure 39: I bought this set of three mics for the pictures in this article; they were just $36 including shipping. Page ATRA. All Rights Reserved.

37 Reading the Micrometer (continued) FOR GOOD MEASURE Choosing the Right Size Mic The first step in using a micrometer is choosing the right size mic for the item you re measuring. Micrometers come in various sizes, but are only designed to measure within a range of about one inch. For example, the set shown in figure 39 includes three micrometers: Zero to 1 inch 1 to 2 inches 2 to 3 inches The thing to remember is that the first digit in your measurement will always be the smaller of the two measurements in the range. That is, if you re using a zero-to-one inch mic, the first digit will always be a zero: 0.xxxx" If you re using a 1-to-2 inch mic, your first digit will always be a 1: 1.xxxx" How do you choose the right size mic? That ll be painfully obvious the first time you try it: The right mic is the one that fits over the object you re measuring, and adjusts tight enough to provide a measurement. If the thimble rotates past the sleeve measurements, and the part you re measuring doesn t fit snuggly between the anvil and spindle, you re using a mic that s too big. If the part won t fit no matter how far you rotate the thimble, the mic s too small ATRA. All Rights Reserved Page 37

38 Reading the Micrometer (continued) Reading the Scale Imperial (Inches) Now we re ready to look at the scale. This is the part of using a mic that s fairly consistent, regardless of what type of mic you re using. Start by looking at the sleeve (figure 40): It has a number of different-size graduations. The largest graduations are numbered from zero to 9. Those each indicate a tenth of an inch, or ". Figure 40: Each of the numbered graduations on the sleeve is equal to a tenth of an inch. Those are divided into four smaller graduations, each equal to ". Each of those graduations is divided into four equal parts. So those smaller graduations are each equal to ", because 4 x " = ". Figure 41: A full rotation of the thimble equals one graduation on the sleeve. And the thimble is divided into smaller graduations; in this case, down to ". Page ATRA. All Rights Reserved.

39 Reading the Micrometer (continued) FOR GOOD MEASURE Reading the Scale Imperial (Inches) (continued) Now look at the thimble (figure 41). Each full rotation of the thimble is equal to one of the small graduations on the sleeve, or ". The thimble is divided into different sized graduations, too. The longest graduations are numbered by fives; each of them is equal to ". Those graduations are divided again; how many times depends on the resolution of your micrometer. In this case, the larger graduations are each equal to "; the smaller equal ", or five ten-thousandths of an inch. That s pretty good, but it s not the limit of our resolution. Take another look at the sleeve. See those extra divisions, running perpendicular to the first set we discussed (figure 42)? That s called the vernier scale; each graduation on the vernier scale is equal to ". So this micrometer can provide measurements that resolve down to one ten-thousandth of an inch! The trick to reading the micrometer is to add the readings on each scale, to provide a single, complete measurement of the object. Figure 42: The vernier scale allows you to refine your measurement even further; down to just " ATRA. All Rights Reserved Page 39

40 Reading the Micrometer (continued) Reading the Scale Imperial (Inches) (continued) Not all micrometers have a vernier scale; in fact, not all mics have a scale that reads down below 0.001" (figure 43). In that case, all you can do is estimate the ten-thousandths measurement, based on the position of the thimble in relation to the spindle. Figure 43: Not all mics have a vernier scale. If yours doesn t, you can estimate the difference between the zero line and the graduations on the thimble. Page ATRA. All Rights Reserved.

41 Reading the Micrometer (continued) FOR GOOD MEASURE Measuring with a Mic Imperial (Inches) Now let s see how to read the micrometer scales to measure an object. For this measurement, I ve chosen a small adjustable wrench. To make the measurement (figure 44): Figure 44: The procedure for measuring an object with an outside mic is always about the same. If you re unsure of the procedures, reread the procedure in the last chapter. Zero the micrometer. Open the micrometer enough to allow the item to fit between the anvil and spindle. Close the micrometer against the area you want to measure, using the ratchet to adjust it against the object without overtightening it. Lock the micrometer spindle using the locknut. If you re unsure of any of these procedures, go back and read the measurement procedures in the last chapter ATRA. All Rights Reserved Page 41

42 Reading the Micrometer (continued) Now we re ready to read the measurement. To make it easier to read and explain, I ve decided to cheat just a bit: I m using a flattened drawing of the micrometer scale, adjusted exactly the way the micrometer displayed its measurement (figure 45). This just makes it easier for you to read the display all at once, without having to rotate the micrometer to see all the different scales. Think of it like using a map of the world instead of a globe; everything s right there in front of # you, instead of having to rotate it to see what s on the back. Figure 45: This is a flattened version of a micrometer scale; like using a world map instead of a globe. It lets you examine all the scales at once, without having to rotate the mic to see the rest of the scale a big benefit in print! # "!! " # $ % & ' Since the micrometer we used was a zeroto-1 inch mic, the first digit will be a zero: 0.xxxx Next we look at the large, numbered graduations on the sleeve. The thimble is back far enough to reveal the third numbered graduation, so the measurement is at least three tenths of an inch. Here s what we have so far: 0.3xxx A closer look at the sleeve reveals at least one smaller graduation is showing; maybe two. So which is it, one or two? It s one; here s how we know: Page ATRA. All Rights Reserved.

43 Reading the Micrometer (continued) FOR GOOD MEASURE Look at the graduations on the thimble (figure 46). Notice we re close to the 20; that is, we re near the end of its scale. Remember, each rotation of the thimble is equal to one small graduation on the sleeve. So, since # we re near the end of the scale on the thimble, we re just Figure 46: Are we seeing one graduation or two past the 3 on the sleeve? It has to be one, because we re too close to the high end of the scale on the thimble. # "!! " # $ % & ' short of the second graduation on the sleeve. That s why we can see a little of the next graduation, even though we haven t reached it yet. Okay, so we have one small graduation showing on the sleeve; that s another ": " " " 2007 ATRA. All Rights Reserved Page 43

44 Reading the Micrometer (continued) Next, look at the graduations on the thimble (figure 47). The zero indicator line on the sleeve is lined up just a bit shy of would be "; since this # is less, it d be Figure 47: The graduations on the thimble tell you how much to add to your initial measurement. In this case, you ll be adding ". # "!! " # $ % & ' ". But there s another, short graduation, between the 20 and 21. That s ", so the thimble reads ". That s how much we add to the formula: " " " " Page ATRA. All Rights Reserved.

45 Reading the Micrometer (continued) FOR GOOD MEASURE But wait; there s more! Notice that the zero indicator is just a tiny bit past the " mark. This is where the vernier scale comes in. Look at the vernier # scale, and find the graduation that # "! Figure 48: To refine your measurement even further, see which graduation on the vernier scale lines up with a graduation on the thimble. Then add that number to the 1 /10,000 ths column.! " # $ % & ' lines up with a graduation on the thimble (figure 48). In this case, it s the 3. That s another " to add to the total. So our final measurement is: " " " " " And that s the final measurement in inches: " ATRA. All Rights Reserved Page 45

46 Reading the Micrometer (continued) Reading a Metric Mic Some of you aren t forced to fight with measuring length in inches, feet, yards and miles. Some of you get to work in simple decimal equivalents, known as the Metric system. For you, there are specially designed micrometers, calibrated in millimeters. One of the first things you might notice about this Metric micrometer is that it doesn t have a vernier scale (figure 49). It only measures down to hundredths of a millimeter. Why aren t Metric micrometers calibrated to resolve as well as an Imperial micrometer? Figure 49: I couldn t find a single Metric micrometer with a vernier scale. The reason is probably because the Metric mic resolves low enough without needing it. Actually, there isn t much difference between the two. Remember, millimeters are a lot smaller than inches: It takes 25.4 of them to equal just one inch. A hundredth of a millimeter equals just under ". So the Metric micrometer provides almost the same resolution as the Imperial one, even without a vernier scale. And you can still approximate more precisely, simply by paying attention to how close the graduations are to the zero line. While there may be some Metric mics with a vernier scale, I couldn t find one. I presume it s because of the inherent resolution in the Metric mics, eliminating the need for a vernier scale. Page ATRA. All Rights Reserved.

47 Reading the Micrometer (continued) Reading a Metric Mic (continued) FOR GOOD MEASURE Figure 50: There are two sets of graduations on the sleeve of the Metric mic: The one above the zero line is in millimeters. The one below is halfmillimeters. The next thing to notice is the scale on the sleeve (figure 50). There are two sets of graduations: one above the zero line and a second below it. The set above the line is the measurement in millimeters: Each graduation equals one millimeter. The set below the line is calibrated in half-millimeters, or 0.5 mm. And the scale on the thimble is divided into 50 graduations. Each rotation moves the thimble a half millimeter, so each graduation on the thimble equals 0.01 mm. Let s use the Metric micrometer to measure the same wrench, and see how close the two measurements are. We ll use the same technique to measure the wrench as before, and then read the scale ATRA. All Rights Reserved Page 47

48 Reading the Micrometer (continued) Reading a Metric Mic (continued) The sleeve shows 8 graduations above the zero line, so it s more than 8 mm, but less than 9 mm (figure 51). And there s one additional graduation showing below the line, so that s another half millimeter. So far, the wrench is at least 8.5 mm. Now look at the thimble. The zero lines up almost exactly with the 28 th graduation (figure 52); that s 0.28 mm. So we add the two measurements: Figure 51: The thimble lines up just past the graduation on the sleeve that s halfway between 8 and 9 millimeters. That puts the measurement at 8.5 mm so far. Figure 52: The zero on the sleeve lines up with the 28 th graduation on the thimble, so you add 0.28 mm to the measurement: the wrench is 8.78 mm thick mm mm 8.78 mm So the wrench is 8.78 mm thick, according to the Metric micrometer. How does that compare with the measurement in inches? = " just " difference in the measurements and that difference could have been caused by position of the mic, pressure, temperature any number of things that are beyond our control. That s all there is to using a micrometer. There are no real tricks nothing special to memorize. It s mostly about taking the time to measure carefully, and to add the measurements together. Or you can get a digital, and leave the math to someone else! Page ATRA. All Rights Reserved.

49 Test Your Measurement Skills In this program, we ve examined how to use and read a wide range of vernier calipers and micrometers. By now, you should either be very familiar with reading these devices, or have given up entirely and bought yourself a digital caliper. Now let s see how well you ve been paying attention. Here are 10 pictures of the scales on various calipers and micrometers. See if you can read them all; write them down in the spaces provided, or on a separate sheet of paper. For the standard vernier caliper, record the measurement in both Imperial (inches) and Metric. Once you think you have them all, turn the page and check your answers. We ll go over each one, to show you how to read them and what they showed ATRA. All Rights Reserved Page 49

50 Test Your Measurement Skills (continued) Vernier Caliper 1. inches # # # E 2. mm! " # $ % & '! " # $ % & '! " # $ % & '! " # $ % & '!! " # $ % & 3. inches # # # E 4. mm! " # $ % & '! " # $ % & '! " # $ % & '!!! " # $ % &! " # $ % & ' 5. inches 6. mm! " # $ % & ' # # # E! " # $ % & '! " # $ % & '!!! " # $ % &! " # $ % & ' Page ATRA. All Rights Reserved.

51 Test Your Measurement Skills (continued) Dial Caliper 7. inches 8. inches Imperial Mic (inches) 9. inches 2007 ATRA. All Rights Reserved Page 51

52 Test Your Measurement Skills (continued) Imperial Mic (inches) 10. inches Metric Mic (millimeters) 11. mm 12. mm Page ATRA. All Rights Reserved.

53 Test Your Measurement Skills (continued) Fractional Caliper 13. inches 2007 ATRA. All Rights Reserved Page 53

54 Test Your Measurement Skills (continued) Vernier Caliper # # # E! " # $ % & '! " # $ % & '! " # $ % & '!! " # $ % &! " # $ % & ' " The zero mark is just before the first numbered graduation. Since each smaller graduation is 0.025", the measurement is more than 0.075" but less than 0.1". Now check the vernier: The 14 th graduation aligns with a mark on the fixed scale, so we add 0.014" to 0.075", for a total of 0.089" mm The zero mark is just past the 2 nd millimeter, so it s between 2 and 3 millimeters. Now check the vernier: The third mark past the 2 aligns with the fixed scale. Since each of the smaller graduations equals 0.02 mm, that s 0.26 mm. Add 0.26 mm to 2 millimeters for 2.26 mm. # # # E! " # $ % & '! " # $ % & '! " # $ % & '!!! " # $ % &! " # $ % & ' " The zero on the vernier is just a tiny bit past the center between 7 and 8; that s 0.75". Now check the vernier: It looks like the 7 th graduation is aligned with the fixed scale, so add 0.007" to 0.75", for a total of 0.757" mm The zero is just a bit past the 19 th graduation on the fixed scale, so it s just over 19 mm. On the vernier, the first graduation past the 2 is aligned with the fixed scale, so add 0.22 mm to 19 mm for mm " The zero is just past the 1.1" mark on the fixed Page ATRA. All Rights Reserved.

55 Test Your Measurement Skills (continued) Vernier Caliper (continued) # # # E! " # $ % & '! " # $ % & '! " # $ % & '!!! " # $ % &! " # $ % & ' scale. It s almost at 1.125" almost, but not quite. The vernier scale aligns with the fixed scale at 21, so the value is 1.1" " = 1.121" mm The zero is almost exactly centered between the 28 th and 29 th graduation, so it s about 28.5 mm. But a closer look reveals that the vernier is aligned at the 46 th graduation, so it s actually mm. Dial Caliper " The fixed scale is past the 2, so it s over 0.2". The needle on the dial is aligned with the 27, so we add 0.027" to 0.2", for a total of 0.227" 2007 ATRA. All Rights Reserved Page 55

56 Test Your Measurement Skills (continued) Dial Caliper (continued) Imperial Micrometer (Inches) " This time the fixed scale is past the larger 1: That s 1". But it hasn t reached the next, smaller 1 on the scale, so it s 1.0". The needle indicates 53, so we add 0.053" to 1.0" for a total of 1.053" " The thimble hasn t moved far enough to reveal any of the numbered graduations, so it s less than 0.1". But there are three smaller graduations showing on the sleeve, so it s more than ". Next, we move to the graduations on the thimble. It s just past the 2 nd large graduation, so we add ", Page ATRA. All Rights Reserved.

57 Test Your Measurement Skills (continued) Imperial Micrometer (continued)) which equals ". Finally, we check the vernier scale. The 3 is aligned with the scale on the thimble, so we add ", for a final total of " " It looks as though the first division past the 2 is visible, but the thimble is right near the 22, which means it s near the end of a rotation. So it s 0.2" on the sleeve, plus 0.022" on the thimble. Then the vernier scale indicates another ", for a total of " ATRA. All Rights Reserved Page 57

58 Metric Micrometer (5) mm Only one graduation is visible on the sleeve, and it s below the line, so that s equal to 0.5 mm. To that we add 0.39 mm shown on the thimble, for a total of 0.89 mm. Extra credit for recognizing that the thimble is actually between the 39 and 40, putting the reading closer to mm mm There are six graduations visible above the line on the sleeve, so it s at least 6 mm. A graduation is almost visible below the line, but the thimble is right near the end of a rotation, so it s less than 6.5 mm. The graduation on the thimble is aligned right at the 42, so this would be 6.42 mm. Page ATRA. All Rights Reserved.

59 Fractional Vernier Caliper /128" = 41 /64" = " This is the fun one depending on your idea of fun. As you can see, the zero mark is two graduations past 1 /2" on the fixed scale. Since each mark on the fixed scale is equal to 1 /16", that s 1 /2" plus 2 /16". A closer look at the vernier shows the 2 nd graduation is aligned with a graduation on the fixed scale. The graduations on the vernier are each equal to 1 /128", so we have to add 2 /128" to the total. So the formula would be: 1 /2" + 2 /16" + 2 /128" =? Next, we have to find a common denominator, so we can add the fractions. The easiest one to use is 128. So the formula becomes: 64 /128" + 16 /128" + 2 /128" = 82 /128" which we can reduce to 41 /64". We can determine the decimal equivalent by dividing 41 by 64, which equals ". So, how d you do? If you got all but the last one, you did terrific. And if you got the last one too, you re a whiz! But if you re still having trouble reading the calipers or mics, either start practicing, or avoid the whole issue by going digital. Because accurate measurements can be critical to providing quality repairs ATRA. All Rights Reserved Page 59