ACCURATE MEASUREMENTS
by Steve Bodofsky
Reading a Micrometer
I
n the last issue of GEARS, we
looked at micrometers: What they
are, basic terminology, and how to
use them. In this issue, we’ll discuss
how to read the scale on a micrometer,
or mic. While there are many different types of mics, the scales are pretty
much the same.
As with the caliper, micrometers
are available in a digital format, and
can be had for a fairly reasonable price
if you’re willing to shop around. For
that matter, a digital caliper will probably provide you with adequate accuracy and resolution for most of your
measurement needs.
But assuming you’re willing to
spend the time necessary, and want to
be sure of the most accurate measurement possible, a micrometer may be
the tool for you. Let’s look at how to
read them, starting with a micrometer
that’s calibrated for Imperial (inches)
measurement.
Choosing the
Right Size Mic
The first step in using a micrometer is choosing the right size mic.
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 1 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
Figure 1: Micrometers come in a wide range of sizes, with
a limited range of measurement. In virtually every case, the
first digit of your measurement will be the lower range of
the mic.
52
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 the
wrong mic.
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 2): 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 0.1000”.
Each of those graduations is divided
into four equal parts. So those smaller
graduations are each equal to 0.0250”,
because 4 x 0.0250” = 0.1000”.
Now look at the thimble (figure
3). Each full rotation of the thimble is
equal to one of the small graduations
Figure 2: 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 0.0250”.
GEARS October 2007
Parts for Automatic Transmissions
SEE YOU IN
LAS VEGAS!
Please call for an appointment with us:
Phones: +49 171 3307071 or +49 151 12116705
[email protected]
www.newco-autoline.de
Reading a Micrometer
on the sleeve, or 0.0250”. The thimble is divided into different sized graduations, too. The longest graduations are
numbered by fives; each of them is equal to 0.0050”.
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 0.0010”; the smaller equal 0.0005”, 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 4)? That’s called the vernier scale; each graduation
on the vernier scale is equal to 0.0001”. So this micrometer
can provide measurements that resolve down to one tenthousandth 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.
TIP:Not all micrometers have a vernier scale; in fact,
not all mics have a scale that reads down below 0.001”
(figure 5). In that case, all you can do is estimate the tenthousandths measurement, based on the position of the
thimble in relation to the spindle.
Figure 3: 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 0.0005”.
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
6):
• 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, read
the Accurate Measurements article in the last issue of
GEARS.
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 7). 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
Figure 4: The vernier scale allows you to refine your measurement even further; down to just 0.0001”.
Figure 5: 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.
�
�
�
�
�
�
�
�
� �
�
Figure 6: The procedure for measuring an object with
an outside mic is always pretty much the same. If you’re
unsure of the procedures, read the Accurate Measurement
column in the last issue of GEARS.
54
�
�
�
�
�
�
�
�
�
Figure 7: This is a flattened version of a micrometer scale; like
using a world map instead of a globe. The advantage is it lets
you examine all of the scales at once, without having to rotate
the mic to see the rest of the scale — a big benefit in print!
GEARS October 2007
)NSIDEEVERY4RANS4ECšKITYOULLALWAYSlNDTHEHIGHESTQUALITYCOMPONENTSTHE
MOSTCOMPLETETECHNICALINFORMATIONANDLOGICALSUBPACKAGING.OBODYMAKES
TRANSMISSIONPARTSMOREDEPENDABLE"ETTERPARTSANDBETTERPERFORMANCE
MEANSLESSCHANCEOFACOMEBACKSOINSISTONREBUILDINGWITHTHEBEST
)NSISTON4RANS4ECšKITSFROM&REUDENBERG./+THE/%SUPPLIERWITH
AFTERMARKETVISION
4s&sWWW4RANS4ECCOMs-ILAN/(
)F)T#OMES"ACKADREVINDD
0-
Reading a Micrometer
using a map of the world instead of a globe; everything’s
right there in front of you, instead of rotating it to see
what’s on the back.
Since the micrometer we used was a zero-to-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:
Look at the graduations on the thimble (figure 8).
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 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 the
second graduation yet.
Okay, so we have one small graduation showing on the
sleeve; that’s another 0.0250”:
0.3000”
+ 0.0250”
0.3250”
�
�
�
�
� �
�
�
�
�
�
�
�
�
�
�
Figure 8: 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.
�
�
�
�
�
�
�
Next, look at the graduations on the thimble (figure 9).
The zero indicator line on the sleeve is lined up just a bit
shy of 21. 21 would be 0.0210”; since this is less, it’d be
0.0200”. But there’s another, short graduation, between the
20 and 21. That’s 0.0005”, so the thimble reads 0.0205”.
That’s how much we add to the formula:
0.3000”
0.0250”
+ 0.0205”
0.3455”
�
� �
�
�
�
�
�
�
�
�
�
�
Figure 9: The graduations on the thimble tell you how much
to add to your initial measurement. In this case, you’ll be
adding 0.0205”.
�
But wait; there’s more! Notice that the zero indicator is
just a tiny bit past the 0.0005” mark. This is where the vernier scale comes in. Look at the vernier scale, and find the
graduation that lines up with a graduation on the thimble
(figure 10). In this case, it’s the 3. That’s another 0.0003”
to add to the total. So our final measurement is:
0.3000”
0.0250”
0.0205”
+ 0.0003”
0.3458”
And that’s the final measurement in inches: 0.3458”.
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
56
�
�
�
�
�
�
�
� �
�
�
�
�
�
�
�
�
�
�
Figure 10: 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 1/10,000ths column.
GEARS October 2007
New SuperFlow TransDyno SF-66K
The convenience, reliability, versatility and ability to test virtually
every transmission on the road, including the new Allison models.
Handles hydraulically and electrically shifted transmissions, foreign
and domestic, in FWD, RWD and AWD configurations. Monitors
and tests virtually every aspect of transmission performance, under
simulated road load conditions, before the transmission is installed
… supported by the accuracy and superior documentation of the
exclusive TDAC (Transmission Data Acquisition & Control) System.
SuperShifter
The NEW Durable
In-Car Tester
Rugged design, solid
state electronics,
impact-resistant housing.
Tests most late model transmissions. Controls
the transmission from inside the car. Tests Solenoid
current/resistance. Operator ID and Date/Time stamp.
Embedded Bluetooth for external device connectivity.
Shown with
manual console.
Valve Body Testers
Precision test valve bodies,
solenoids and pressure
transducers with actual
transmission pressures and
heated oil under toughest
simulated driving conditions.
Solenoid Testers
A must for testing the
weakest link … six at
a time. Easy to use.
TCRS Torque Converter Test and Rebuild Systems
Excellent profit center for transmission repair shops or stand-alone startups …
and smartest way to save time and prevent costly comebacks.
Single Gun Auto Weld Aligner
Standard of the industry.
And choice of the big three
— Ford, GM, Daimler-Chrysler.
Air-operated collets. Patented
auto-tack and auto-weld.
Do “bowl buildups” and
weld on impeller hubs.
TAC 12+ control panel lets
you automatically control
number of tacs and duration.
New! Improved!
Torque Converter
Balancer
now with automatic
weight indexing,
runout compensation mode, push
buttom polishing
and better accuracy
and repeatability
than ever before.
Check out converters
BEFORE you ship or
install with HUB RUNOUT
INSPECTION UNITS. And,
ensure your converter
quality (after welding)
with AIR TEST STANDS
for diagnosing leaks.
Hicklin Heavy-Duty
Transmission Dynamometers
for trucks, mass transit, military, off-highway. In-line v-drive … angle drive … Allison,
Renk, ZF, Voith and many others. Also ask
about towing, axle and brake dynamometers
for medium- to heavy-duty trucks; and
torque converter dynamometers for testing
under real-world, full-load conditions.
SuperFlow Dynos and Flowbenches
Recognized world leader in flowbench technology, plus a
wide range of engine dynos, chassis dynos and software.
Helps OEMs, high performance test engineers and engine
builders take performance to the next level.
www.superflow.com
superflow ad.indd 31
8354 Gears_TestCenterAd_Dec2006.1 1
When you
really need
to know…
4060 Dixon Street • Des Moines IA 50313 • ph: 888-442-5546 or 515-254-1654 • fax: 515-254-1656
12/26/06 11:38:48 AM
12/13/06 4:27:02 PM
Reading a Micrometer
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 11). It only measures down to hundredths of a millimeter. Why aren’t Metric micrometers calibrated to resolve
as well as an Imperial micrometer?
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 0.0004”. 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.
NOTE: 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 it. If anyone has a Metric mic with a vernier scale,
I’d be happy to use it to add a section to the upcoming
booklet for the ATRA web site.
The next thing to notice is the scale on the sleeve
(figure 12). 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 halfmillimeters, 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.
The sleeve shows 8 graduations above the zero line, so
it’s more than 8 mm, but less than 9 mm (figure 13). 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 28th graduation (figure 14); that’s 0.28
mm. So we add the two measurements:
8.50 mm
+ 0.28 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? 8.78 ÷ 25.4 = 0.3457” — just 0.0001”
difference in the measurements… and that difference could
have been cause 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!
58
Figure 11: 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.
Figure 12: 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 half-millimeters.
Figure 13: 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 14: The zero line on the sleeve lines up with the 28th
graduation on the thimble. That means you have to add 0.28
mm to the earlier measurement. So the wrench is 8.78 mm
thick.
GEARS October 2007
Together, we can move in a new direction. Park, Reverse, Neutral, Drive.
Seal Aftermarket Products allows you to shift into gear with OE technology from Parker’s Seal Group; our
strength is backed by 60 years of manufacturing experience dealing with customers demanding the best in
sealing technology. The Seal Group consistently adds manufacturing capabilities through strategic acquisitions
including Acadia Rubber, Wynns Precision and Goshen Rubber, just to name a few.
Seal Aftermarket Products utilizes Parker Seal Group manufacturing capabilities with market leading
technology in developing aftermarket solutions. Seal Aftermarket Products offers kits and bulk
components in over 20 different product categories; Our manufacturing capabilities include many of the
best-known and most reliable products in the industry such as molded pistons, standard and custom
o-ring seals, lip seals, lathe cut seals, Teflon™ seals, and metal clad seals.
Benefit from the total Parker solution and get ready to move.
www.parker.com 1 800 582 2760
15750 NW 59th Avenue
Miami Lakes, FL 33014
GEARS.indd 1
9/17/2007 4:14:06 PM