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Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Shop safety Shop math Introduction to blueprint reading Tolerance interpretation Measuring devices
Lesson Topics
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
A machine shop is a dangerous place! We cannot prepare you for every dangerous situation You must always be alert
Safety equipment Protective eyewear Clothing Hearing protection Safety shoes Helmets Gloves Respirators and facemasks First aid kits Fire extinguishers Cranes and hoists Warning signs
Shop safety
Safety practices When in doubt, ask! Raw material handling
Heavy, sharp, greasy, slippery, dirty, sharp edges, chip residue, awkward shape
Finished workpiece handling In addition to raw material handling:
Hot Spring
Tightening and loosening fasteners Getting around in the shop Behave in a professional manner
No horseplay! Machining-center-specific safety issues
Safety interlocks, guarding, signs, safe operating procedures
Next topic: Shop math
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Calculator recommendations Keep it simple Watch out for trick functions Avoid solar powered calculators Big buttons-big display Clear entry button
Next topic: Blueprint reading
Shop math
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Arithmetic operations
Most CNC operator work can be done with the four basic arithmetic operators:
Add (+): Subtract (-):
Multiply (X or *): Divide (/):
3 + 4 = 77 - 4 = 32 * 9 = 18 20 / 2 = 10
Entries into CNC machines are done in decimal format (fractions are never used)
1/8 = 0.1253/16 = 0.1875
You may be able to do some calculations in your head
20 / 2 = ? (20 divided by 2)
2.5 + 0.5 = ?
3.0 - 0.25 = ?
5.25 + 8.75 = ?
109.75 - 3.5 = ?
But don’t hesitate to use your calculator if you’re in doubt
125.352 - 13.837 = ?
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Arithmetic expressions
An expression is a math question to be answered…
3 + 4 = 7
Question
Answer
4 + 6 – 2 = ?
7 – 3 + 5 = ?
10 * 2 / 5 = ? (10 times 2 divided by 5)
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Priority of arithmetic operations
Consider this expression:
4 + 12 / 4 = ?
What answer did you come up with?
16
16 divided by 4 is 4, right?
But wait a minute – there is another way to do this…
4 + 12 / 4 = ?
3
4 plus 3 is 7
Which answer is correct?
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Priority of arithmetic operations
With no other math “punctuation”… … division has a higher priority than addition
4 + 12 / 4 = ?
3
4 plus 3 is 7
The correct answer is 7
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Priority of arithmetic operations
Parentheses can be used to specify operation order
( )
(4 + 12) / 4 = ?
This makes it clear that 4 must be added to 12 first. Then the result (16) is divided by 4. The answer is 4.
Order of arithmetic priorities:
1) Anything in parentheses
2) Functions (like square root, sine, cosine, tangent)
3) Multiplication
4) Division
5) Addition
6) Subtraction
3 * (4 + 2) = ?5 + 0.5 / 2 = ?(8 + 2) / 5 = ?
7 + 9 / 2 = ?4 + 1 / 2 - 2 = ?8 * (2 + 3) / 2 = ?
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Using a formula
A formula is an arithmetic expression that contains variables
rpm = 3.82 * sfm / tool diameter
rpm represents spindle revolutions-per-minute
sfm represents speed in surface-feet-per-minute
tool diameter represents the diameter of the cutting tool
With this formula, consider this situation:
You need to drill a 0.5 in diameter hole and the cutting tool manufacturer recommends 80 surface feet per minute.
rpm = 3.82 * 80 / 0.5
What rpm will you use?
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measurement systems
Some companies in the United States use the Imperial system
Other companies use the Metric system (the Metric system is used almost exclusively in other countries)
The inch is the most basic unit of distance in the machine shop
The millimeter is the most basic unit of distance in the machine shop
How big is an inch?
A deck of playing cards is about ½ an inch
How big is a millimeter?
The thickness of a quarter-dollar is about one millimeter
One inch = 25.4 millimeters One millimeter = 0.0397 inches (about one-twenty-fifth of an inch)
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measurement systems
To convert millimeters to inches: To convert inches to millimeters:
inches = millimeters / 25.4 millimeters = inches * 25.4
How many inches is 350 millimeters? How many millimeters is 3.5 inches?
Shop math
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Decimal places
A whole number is called an integer Consider this real number:
4, 5, 8, 44, 103, 3,373, and 26,252 are examples of integers
5.436
3.274 is an example of a real number
Shop math
A number containing a portion of a whole number is called a real number
In a real number, the values to the right of the decimal point are called decimal places
There are three decimal places to the right of the decimal point
With most CNC machines…
Metric system allows up to three decimal places
Imperial system allows up to four decimal places
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Fractional format
When using the Imperial measurement system (not the Metric system)…
Consider this fraction:
But a CNC machine cannot accept fractional format
Fractions must be converted to decimal format
Shop math
Some values may be specified with fractions
To convert a fraction to decimal format, divide the numerator (top or left number) by the denominator (bottom or right number)
13/16Pronounced as “thirteen-sixteenths”
Divide 13 by 16
0.8125 (the result) is the decimal format of 13/16
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Saying numbers out loud in a machine shop
In the Imperial measurement system: 1.0 : “one inch”
0.1 : “one-hundred-thousandths of an inch”
0.01 : “ten-thousandths of an inch”
0.001 : “one-thousandth of an inch”
0.0001 : “one tenth” (even though this value is really one ten-thousandth of an inch)
Shop math
More examples:0.047 : “forty-seven thousandths”0.250 : “two-hundred-fifty thousandths”0.684 : “six-hundred-eighty-four thousandths”1.455 : “one inch, four-hundred-fifty-five thousandths”4.3723 : “four inches, three-hundred-seventy-two thousandths, and three tenths”
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Saying numbers out loud in a machine shop
In the Metric measurement system:
1.0 : “one millimeter”
0.1 : “one-hundred microns”
0.01 : “ten microns”
0.001 : “one micron”
Shop math
More examples:0.047 : “forty-seven microns”0.250 : “two-hundred-fifty microns”0.684 : “six-hundred-eighty-four microns”1.455 : “one millimeter, four-hundred-fifty-five microns”
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Polarity
All values have a polarity (plus or minus)
Shop math
With CNC machines, plus is always assumed
If no polarity sign is specified (+ or -), the value is assumed to be positive
All values shown to this point have been positive
To specify a negative value, the minus sign (-) is used:
-0.003 (negative three thousandths of an inch)
When you subtract a number from a smaller number, the result will be negative
5.002 - 5.006 = -0.004
Next topic: Blueprint reading
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Summary
Most calculations required of setup people and operators are pretty simple
Shop math
The trick lies in doing simple calculations – over and over again – with out making any mistakes!
Next topic: Blueprint reading
Mistakes will, of course, result in scrap parts – or worse
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Blueprint reading
Orthographic projection
Blueprint reading involves visualizing a three-dimensional workpiece from a series of two-dimensional views.
The manner in which the two-dimensional views line up is called orthographic projection.
With orthographic projection, there can be as many as six standard views.
Consider one of a pair of dice…
This shows all six views the six standard views used with orthographic projection
Notice how each view is lined up with other views
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Orthographic projection
The way that views line up is key to visualizing what the workpiece looks like.
In addition, line appearance is also important:
Visible line – Surface is visible when looking at the workpiece from the view:
Hidden line – Surface is not visible when looking at the workpiece from the view:
Center line – Represents the center of an object (like a hole):
Notice that hidden lines and center lines are thinner than visible lines
Blueprint reading
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Blueprint reading
Visible line
Hidden line
Center line
Visible line
Hidden line
Center line
Front RightLeftBack
Top
Bottom
Orthographic projection
Here is another example:
All six views are still being shown:1) Front view (plan view)2) Top view3) Bottom view4) Left view5) Right view6) Back view
Notice the three line types
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Blueprint reading
Visible line
Hidden line
Center line
Visible line
Hidden line
Center line
Front RightLeftBack
Top
Bottom
Orthographic projection
Design engineers will rarely show all six views
They will only show enough views to adequately define the workpiece
These three view show enough to allow visualization of the workpiece
Unfortunately, design engineers vary when it comes to how much they show
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Section lines are used to show what the workpiece would look like when cut along the section line
Blueprint reading
Orthographic projection
Section line
Sectional view
They help clarify what a complex workpiece looks like
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Blueprint reading
Orthographic projection
An isometric view is almost like a photograph of the workpiece
Though rarely used, isometric views make it much easier to visualize the workpiece
Isometric view
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Sample workpiece
It really helps to have an actual workpiece when you are studying a blueprint
CNC operators will have an actual workpiece because the setup person will have run at least one during setup
But setup people and programmers will not have one – they must be able to visualize the workpiece from the blueprint alone
Blueprint reading
Next topic: Tolerance interpretation
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Dimensioning
Dimensions provide information about the size of each workpiece attribute
1.0
2.5
1.5
4.25
4.25
2.12
3.0
3.75
.5
.62
1.0
.25
Blueprint reading
While blueprints are drawn to scale, they are rarely full-scale
If you take a ruler to this distance, it will not be 1.0 inch!
Dimensions can be specified in the Imperial (inch) or Metric system
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
6.35 (typical)
19
100
63
19 63
100
13.7
19
13 R (4)
Drill 12.0 dia.
Blueprint reading
Next topic: Tolerance interpretation
Example
Can you visualize what this part looks like?
Can you approximate how big it is?
This workpiece is dimensioned in Metric
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Blueprint reading
Example
Can you visualize what this part looks like?
Can you approximate how big it is?
Next topic: Tolerance interpretation
This workpiece is dimensioned in inches
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Introduction to tolerances
A tolerance specifies the amount of allowable error for each workpiece attribute – and every workpiece attribute will have a tolerance
2.0
1.0
5.0
Say the tolerance is specified as plus or minus 0.005 inch
This means the overall length could be as short as 4.995 in or as long as 5.005 in and still be acceptable
Consider the 5.0 inch overall length of this workpiece
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Important tolerance terms
2.0
1.0
5.0
Consider the 5.0 inch overall length of this workpiece
Tolerance band – from the low limit to the high limit (4.995 – 5.005 is the tolerance band)
Mean value – Right in the middle of the tolerance band (5.0)
Low limit – The smallest acceptable value (4.995)
High limit – The largest acceptable value (5.005)
Overall tolerance – total amount of tolerance – high limit minus low limit (0.010)
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Judging acceptability
2.0
1.0
5.0
Consider the 5.0 inch overall length of this workpieceSay you measure the workpiece length and
find it to be 5.002
Is it acceptable?
Yes – 5.002 is between 4.995 and 5.005
But what if it comes out to 5.006? Is it acceptable now?
No – 5.006 is larger than the high limit
Or if it comes out to 4.994? Is it acceptable?
No – 4.994 is smaller than the low limit
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
What are you shooting for?
2.0
1.0
5.0
Consider the 5.0 inch overall length of this workpieceWhen a workpiece attribute is not within its
tolerance band, an adjustment must be made
The attribute must be brought to its target value
In many companies, the target value is the mean value of the tolerance band (5.0 in our example)
The adjustment amount will be the difference between the measured value and the target value
If you measure the overall length and find it to be 5.007…
…the adjustment amount will probably be 0.007 (assuming target value is the mean value)
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Adjustment polarity
2.0
1.0
5.0
Consider the 5.0 inch overall length of this workpieceEach adjustment will have a polarity (plus or
minus)
Generally speaking:
If more material must be removed, the adjustment polarity will be negative
If less material must be removed, the adjustment polarity will be positive
If you measure the overall length and find it to be 5.007…
…more material must be removed – meaning the adjustment will be negative
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Types of tolerance specifications
Plus or minus tolerance:
5.0 +/- 0.005
Mean value
Attribute can be evenly larger or smaller than mean value by…
…this amount
• Mean value: 5.0• High limit: 5.005• Low limit: 4.995• Tolerance band: 4.995 – 5.005• Overall tolerance: 0.010
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Types of tolerance specifications
High and low limit:
4.995 / 5.005
Low limit
• Mean value: 5.0• High limit: 5.005• Low limit: 4.995• Tolerance band: 4.995 – 5.005• Overall tolerance: 0.010
High limit
Mean value = (high limit + low limit) / 2Mean value = (5.005 + 4.995) / 2Mean value = (10.0) / 2Mean value = 5.0
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Types of tolerance specifications
Uneven plus and minus:
• Mean value: 5.0• High limit: 5.005• Low limit: 4.995• Tolerance band: 4.995 – 5.005• Overall tolerance: 0.010
5.002 +0.003, - 0.007
Starting specificationAttribute can be larger than specified value by this amount
…or smaller than the specified value by this amount
High limit = Starting specification + 0.003 (5.005)
Low limit = Starting specification - 0.007 (4.995)
Mean value = (high limit + low limit) / 2 (5.0)
Next topic: Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Tolerance interpretation
Implied tolerances
Next topic: Measuring devices
Again, every workpiece attribute will have a tolerance
If it is not specified as part of the dimension, it is implied with decimal places
Somewhere on the blueprint, usually near the title block, you will see something like this…
x.x: +/-0.01x.xx: +/-0.004x.xxx: +/-0.002x.xxxx: +/-0.0005
An attribute dimensioned with:
4.75
has a tolerance of +/-0.004 (with this example)
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
General suggestion for getting started with any measuring device
Most measuring devices require that you master a certain “feel” to be proficient
Find something with a known size on which to practice
When the measuring device shows this size, you know you have applied the correct pressure to the device
When you measure an actual workpiece, you’ll know the correct pressure to exert
Gauge blocks or gauge pins have their sizes etched right into each component
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Measured-value display methods
There are three common ways that measuring devices can display measured values
Vernier scale – Most difficult to read, but very common
Dial display – Much easier to read, and still quite common
Electronic digital display – Easiest to read, but more expensive
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
All measuring devices have a limited range for measuring
You must know the starting point for measuring
Range of measurements
A six-inch caliper has a range of six inches and its starting point is zero
A “zero-to-one” micrometer has a range of one inch and its starting point is zero
A “two-to-three” micrometer has a range of one inch and its starting point is two inches
Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Many measuring devices have some kind of pointer
You must often add the reading you take to this pointer position
Pointer position
With a six inch caliper, the pointer may be on 4.2 inches, meaning you must add the read value to 4.2
With a “zero-to-one” micrometer, the pointer may be on 0.45, meaning you must add the read value to 0.45
Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Vernier scale value display
This Vernier caliper allows measurements in both Imperial and Metric (few do)
Inch scale
Metric scale
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Vernier scale value display
Each Vernier scale will have a main scale…
Main scales
Vernier scale
Vernier scale
… and a Vernier scale
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Vernier scale value display
The origins for these main scales (not shown) are zero
0
Origin would be about here
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Vernier scale value display
The pointers for the Vernier scales are here
0
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Vernier scale value display
To read the displayed value…
0
The Metric pointer is pointing at just over 2.4 cm (24 mm)
The Vernier scale line that best lines up with the main scale is 0.062 cm (0.62 mm)
Add the two together – 2.4 cm (24 mm) plus 0.062 cm (0.62 mm) totals 2.462 cm (24.62 mm)
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Dial display
Dial displays are usually much easier to read
First find the main scale pointer
It is pointing to just over 0.5 inch
Now find the dial reading…
It is centered between 0.010 and 0.011 (0.0105)
The reading is 0.5105
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
Electronic digital display
Digital displays are the easiest to read
With this 25-50 mm micrometer, the starting value (pointer) is 25 mm
The digital display directly shows the measured value (25.000 mm at the present time)
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Measuring devices
External workpiece attributes
Some measurements involve measuring over external surfaces
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Internal workpiece attributes
Other measurements involve measuring internal surfaces
Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
General use: The knurled handle is turned to move the spindle face from the anvil face far enough to place the workpiece attribute between them. The knurled handle is then turned in the opposite direction to gently clamp the workpiece between the anvil face and the spindle face. For final clamping, the ratchet is used (turned in the same direction as the knurled handle) to apply the appropriate amount of force. Finally, the locknut can be tightened to lock the thimble in place – the micrometer can then be removed from the workpiece attribute (if necessary) for easier reading.
Locknut
Anvilface
Spindleface
Spindle
Sleeve
Thimble
RatchetFrame
Knurledhandle
Application: External workpiece attributesAccuracy expectation: +/- 0.0001 in or +/- 0.004 microns
Micrometer
Measuring devices
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Depth micrometer
Measuring devices
General use: The knurled handle is turned to retract the spindle until it is shorter than the depth to be measured. The base face is then placed on the upper surface for the measurement and held firmly in place. The knurled handle is turned in the opposite direction to bring the spindle face into contact with the lower surface and retracted slightly. For final contact, the ratchet is used (turned in the same direction as the knurled handle) to apply the appropriate amount of force. Finally, the locknut can be tightened to lock the thimble in place – the depth micrometer can then be removed from the workpiece attribute (if necessary) for easier reading.
Application: Internal depth attributes.Accuracy expectation: +/- 0.0001 in or +/- 0.004 microns.
Spindleface
Base face
Spindle
Locknut
Sleeve
ThimbleRatchet
Knurledhandle
Vernier display
Lesson topics
CNC Machining Center Setup and OperationLesson 1:
Basic machining practices required for machining centers
Copyright 2009
Stationary side
Internal calipers
External calipers
Sliding side
Scale indicator surface
Scale
Dial
Dial locknut
Slide
Knurled thumb knob
Slide locknut
End stylus
Slide end
Dial caliper
Measuring devices
Application: External and internal workpiece attributes.Accuracy expectation: +/- 0.0005 in or +/- 0.010 microns.
General use: For external measurements, the slider is pulled (with the knurled thumb knob) to widen the external calipers wider than the attribute to be measured. The external calipers are then placed over the attribute and the tightened to squeeze the attribute (care must be taken to confirm square ness). The reading can be taken at this point.
For internal measurements, the slider is pulled (with the knurled thumb knob) to widen the external calipers just narrower than the attribute to be measured. The internal calipers are then placed inside the attribute and the pulled apart to engage the attribute (care must be taken to confirm square ness). The reading can be taken at this point.
For end (depth) measurements. The slide end is butted against the upper surface (care must be taken to ensure square ness). The knurled thumb knob is then pulled to open the calipers until the stylus end contacts the other surface. A reading can be taken at this point.